Wind Turbine Generator

Background…
A generator is much like a motor in that it is made of coils of wire and magnets, and it works through electromagnetic induction. However, a generator has an input of mechanical energy and an output of electrical energy. In the case, the input is the spinning blades of the turbine, and the output is the lightbulb shining.

Materials and Methods…
For our generator, we used the fan blades from a window fan we took apart and two-coils of wire wire along with four magnets (where induction would take place). We attached this to a three wooden dowels and mounted it on a platform.



Results…
The amount of voltage produced is affected by the number of coils you use: the more coils, the greater the voltage. Voltage will also be greater if the turbine spins faster, because there is a greater input, resulting in a greater output. Our group worked efficiently and did not run into any particular trouble during this project. The best advice I can offer to future physics students is to think carefully about your materials. Adhesives can be particularly tricky when it comes to assembling a large variety of materials. Try to keep things simple. Also, disassembling a fan to use the blades was very effective and made it easier to focus on lighting the lightbulb rather than worrying about assembling a makeshift fan.

The Top Ten Most Memorable Physics Concepts

1.) Newton's First Law
Newton's First Law states: An object at rest stays at rest and an object in motion stays in motion unless acted upon by an outside force. This means that if I threw a ball, and no forces were present to stop that ball, it would continue on in the direction I threw it for eternity, or until something blocked its path. In other words, objects are lazy. Inertia is how hard it is for something to start and stop. The most important thing to remember, is that INERTIA IS NOT A FORCE, it is a principal. After learning about Newton's first law and inertia, I now understand why certain objects do and do not move, and how this is possible. The following video I created with my group illustrates these properties:

 

2.) Newton's Second Law
 Newton's second law states: force is proportional to acceleration and inversely proportional to mass (a=F/m). This means that the more force applied to an object, the more it will accelerate. It also means that as mass increases, acceleration decreases.
Take this car for example:

We are given the car's mass and acceleration, but we don't know how much force is acting on the car. We can use Newton's Second law to solve for the force.
a = f/m
0.5 m/s = F/1000 kg
F = 500 N

3.) Newton's Third Law
Newton's third law states that for every action, there is an equal and opposite reaction.

This picture of a book on a table is an example of an action reaction pair. The book pushes the table down and the table pushes the apple up. The table is resting on the ground, so the table pushes the earth down, and the earth pushes the table up. The earth is also reacting to the apple, so the earth pulls the apple down, and the apple pulls the earth up. 

Each of these action reaction pairs can be represented with arrows of equal length going in opposite directions. The format with which one writes an action reaction pair is as follows: 

Bat                        hits                 ball forward

Ball                       hits                 bat backward

Switch nouns       same verb        opposite directions

Newton's third law is reiterated in the following video:

4.) Center of Mass/Gravity
All objects have an average position of their mass, called their center of mass. When gravity acts on that center of mass, it is called center of gravity. Center of gravity affects balance. When an object's center of gravity is inside of its base of support, it is less likely to fall over than when it center of gravity is outside of its base of support. When center of gravity is outside of the base of support, a lever arm is created, and the force of gravity gives the object torque, causing it to fall over.
This is exemplified in the following image:

The object with the smaller base of support will fall over because its center of gravity is outside of its base of support, while the large one will remain standing. As a clumsy person, this was one of my favorite things we learned about. Now I know why I fall over.

5.) Machines

Machines help us use our energy more efficiently by reducing the amount of force needed to move an object. In this unit, we addressed simple machines. A prime example of a simple machine is the inclined plane. As previously mentioned, work = F x d. The inclined plane, and all other simple machines, increase the distance an object moves, in turn decreasing the force needed to move it. Although the force exerted is decreases, the work will remain the same as it would have been lifting an object over a short distance. 

In this image, a man is pushing a 200 N object up an inclined plane of 12m. The ramp has a vertical height of 8m. The work that would be done if the man lifted the 200 N straight up 8m is called the workout. The work done pushing the weight up the 12m ramp is called the workin. We can use the following equation to solve for the amount of force needed to push the object up the ramp.

work = force times distance

workin = work out

Fin x din = Fout x dout

F x 12 = 200 x 8

12F = 1600

F = 133.3 N

As you can see, the workout = the work in, but the force required to push the object up the ramp is smaller than the force required to lift it straight up. 

Machines are important, because we see and use them everyday. It is nice to know the reasoning behind what makes doing things feel easier.

6.) Tides

The force between the earth and the moon is what creates tides. The force between the moon and the earth is greater than the force between the sun and the earth. This is because the opposite sides of the earth experience a difference in force. It is also what causes tides. The side of the earth facing the moon and the opposite side will experience high tides, while the other sides experience low tides. As the earth spins every place will experience 2 high tides and 2 low tides a day. Tides are not at the same time every day because the moon moves as well. What about the moon and earth in relation to the sun. When they are all aligned, we experience tides at their extremes, high highs and low lows. These are called spring tides and occur during new and full moons. When they are not aligned, we experience neap tides, which are higher low tides and lower high tides. These occur during half moons.

Tides are important because they happen every single day. They are especially relevant to people who live on or near the beach. 

7.) Lightning
Induction and polarization are the reasons lightning occurs. Air circulation causes clouds to polarize, with positive charges one top and negative charges on bottom. This causes the ground to do the same in response. The opposite charges between the cloud and the ground equalize, and energy is produced in the forms of light, heat, and sound (lightning).

Lightning is one of my favorite things I've learned in physics because it is such a phenomenon. Before taking this class, I had no idea what created the flashes in the sky. Now I do, and the concepts behind it are very interesting.

8.) Parallel and Series Circuits

A circuit is any path along which electrons can flow. There are two different types of circuits: series and parallel. Series is a single pathway for electron flow and parallel has branches, each a separate path for electron flow. 

                                                     Series                                 Parallel

In a series circuit, the sum of resistance in a circuit is the sum of individual resistance along the pathway. If one device fails, the circuit is broken, stopping current and causing the other devices to stop working. 

In a parallel circuit each device operates independently and connects to the same two points of the circuit. A break in one path will not affect the other branches in a parallel circuit. The total current is the sum of the current in the parallel branches. As the number of branches in a parallel circuit increase, the resistance of the circuit decreases. This can cause overheating and fire. Fuses protect from fire by melting when the current in a parallel circuit is too large. It is connected to the beginning of the circuit, so when the fuse melts, all of the devices will cut off. 

This is important because it explains what powers our homes by telling us how they are wired. It also helps keep us safe by knowing that fuses are necessary to prevent fire. 

9.) Magnets

The source of all magnetism is moving charges. Magnetic materials have north and south poles. Magnetic field lines move toward the north pole on the inside and the south pole on the outside.

Materials have what are called domains, which are groups of atoms whose electrons are spinning in the same direction. Domains are typically oriented in all different directions. When an object becomes magnetized, its domains align, giving it north and south poles.

This was one of my favorite physics concepts because it explains why things become magnetized. I loved playing with magnets as a kid, especially this toy:

Who knew it had anything to do with physics?! :)

10.) Electromagnetic Induction

Electromagnetic Induction is when voltage is induced by changing the magnetic field in loops of wire.

The more coils in an electromagnet, the more voltage is induced. 

A common example of electromagnetic induction is the use of credit cards. Credit cards have magnetic strips with sectors oriented in different ways. A card reader has small coils of wire, which are induced with voltage when the card slides through. These electrical signal from the card are interpreted by the reader into a code. 

People use credit cards on a daily basis. It interesting to know the physics behind our purchases.

I chose these concepts because they are the ones that have stuck with me most throughout the year. Whether it's the expanse of knowledge they encompass or their applicability these are the concepts I will remember long after the the physics course is over.

Unit 7 Reflection

In this unit I learned about…

Magnetism, Magnetic Poles, and Electromagnetism
The source of all magnetism is moving charges. Magnetic materials have north and south poles. Magnetic field lines move toward the north pole on the inside and the south pole on the outside.

Materials have what are called domains, which are groups of atoms whose electrons are spinning in the same direction. Domains are typically oriented in all different directions. When an object becomes magnetized, its domains align, giving it north and south poles.

You may be wondering then, why all materials aren't magnetic. The answer is simple: not all materials have domains.

Knowing about north and south magnetic poles, we know why the northern lights occur. Harmful particles called cosmic rays sometimes hit the earth's atmosphere. We are not negatively affected, because the earth itself has magnetic poles, so the particles hit the earth's magnetic field and spiral along the field lines to the poles. The beautiful waves of light and color seen are the result of these cosmic rays.

Much like with positive and negative charges, like poles repel and opposite poles attract. This is because, when north and south pole are near one another, their field lines are moving in the same direction. The opposite can be said when two north or two south poles are near one another.

So, how does something become magnetized?  A common example of an object being magnetized is a paperclip and a magnet:
Domain in a paperclip are random. A magnet has a magnetic field. When the magnet gets close to the paperclip, the domains of the paperclip align with the magnetic field of the magnet. The paperclip now has north and south poles. The north pole of the paperclip is attracted to the south pole of the magnet, so the paperclip stick together. The paperclip can become unmagnetized if it exposed to heat or jostled, because the domain become unaligned.

An electromagnet is a current-carrying coil of wire. Its strength is increased by increasing the number of turns in the coil and the current.

Forces on Charged Particles in an Electric Field; Motors
Particles in an electric field are moving and are affected by a magnetic field. We can use the right hand rule to find the direction of the magnetic field. Point your thumb in the direction of the particle's movement, and curl your finger's around. Your curling fingers are the direction of the magnetic field.

For information on how a motor works, refer to my previous post, in which I describe the lab where we made a simple motor.

Electromagnetic Induction

Electromagnetic Induction is when voltage is induced by changing the magnetic field in loops of wire.

The more coils in an electromagnet, the more voltage is induced. 

A common example of electromagnetic induction is the use of credit cards. Credit cards have magnetic strips with sectors oriented in different ways. A card reader has small coils of wire, which are induced with voltage when the card slides through. These electrical signal from the card are interpreted by the reader into a code. 

Generators and Energy Production

Generators produce energy through electromagnetic induction. This is usually done by rotating a coil with a stationary magnetic field. The difference between a generator and a motor is that a generator transforms mechanical energy (input) into electrical energy (output), while a motor does the opposite. They are both made of could of wire and magnets, and they both work through electromagnetic induction. 

Transformers

A transformer is a device for increasing or decreasing voltage or transferring electric power from one coil of wire to another by means of electromagnetic induction. Transformers have an input (primary) and an output (secondary). They are used to either step up (increase) or step down (decrease) voltage. Stepping up voltage decreases current and stepping down voltage increases current. In order for voltage to be stepped up, the secondary coil of wire must have more turns than the primary coil. For voltage to be stepped down, the secondary coil of wire must have less turns than the primary coil. 

primary voltage/number of turns = secondary voltage/number of turns

Step up:

Step Down:

Whether the voltage is stepped up, stepped down, or the same the power in and out will always be equal. 

power into primary = power out of secondary

Electric power equals voltage (V) times current (I). This means,

VI primary = VI secondary
We can use this equation to solve or unknown current or voltage in the system.

Note: Transformers and generators must both use alternating current (AC). This is because both function from electromagnetic induction, which occurs when the magnetic field changes. In order for the magnetic field to change, the current must alternate.

My problem solving skills, effort, and learning…

In this unit, I have completed all of my assignments on time and prepared well for all assessments. I learned about magnetism and how much it affects everyday life. I didn't realize how much it had to do with electricity and power companies.

Goals…

-to prepare well and ace the exam!

Making a Simple Motor- Lab Reflection

Parts of the motor and their function:
Battery: Energy source
Coil of Wire: Conductor
Paperclip: Connects/ completes the motor circuit by holding the coil of wire to the positive and negative ends
Magnet: Magnetizes/ aligns domains (keeps circuit moving)



Armature
The armature (part of the wire) had to be stripped, because it was insulated and would not complete the current, had it remained insulated. The armature had to be scraped precisely, so the coil of wire would make a full rotation, and a pulse of current would be sent every time the coil of wire turned, rather than all the time (this would result in a short circuit).

Why the motor turns...
The motor turns, because the coil of wire becomes magnetized (carries current). The magnetic field in this system moves around the current-carrying wire in a circular manner. According the the right hand rule,

Since the magnetic field is moving in a circular pattern, the force will push the coil around. Current travels through the entire system, while the force turns the coil in accordance with the right hand rule.

Video of a simple motor in action...

Note: Unfortunately, my group experienced some technical difficulties trying to get our motor to function properly. This video is from Joey, Michael, and Mo, who did a great job!

What it could be used for…
This motor would be best used in small objects requiring motors, like toy cars.

Unit 6 Reflection

In this unit I learned about…

Charges, Polarization, and Coulomb's Law

There are two types of charges: protons (positive) and neutrons (negative). Like charges repel and opposite charges attract. Objects are usually neutral (not charged), meaning they have an equal amount of protons and neutrons. Objects can become charges (have and imbalance of electrons and protons) through three different ways: contact, friction, and induction.

An example of how something becomes charged through friction:

When a sweater rubs against your head, making your hair stand up…
The sweater rubs against your head, stealing electrons through friction. This means there are now more protons than electrons in your hair, making it positively charged. Since like charges repel, and there are more protons than electrons, your strands repel one another, causing them to stand up.

Induction:

Induction is a form of charging something without touching. This can be seen in lightning, which I will explain later.

Contact:

When you touch something or someone, like charges repel and opposites attract (what you feel when you shock someone).

Polarization is when opposite charges separate from each other to opposite areas of an object. The object is still neutral. This is why a balloon sticks to a wall after you rub it against your head.

The balloon is charged by friction when it rubs against your head, making it negative. When the balloon touches the wall, the wall polarizes. The positive charges are attracted to the negative balloon and the negative charges repel away from the balloon. We won't be able to understand this unless we know Coulomb's law (F=kq1q2/d^2). This means that force equals charge over distance. The smaller the distance between charges, the more force they fell. Coulomb's law tells us that the attractive force is greater than the repulsive force, because the opposite charges are closer to one another. Since there is a greater force between the opposite charges than the like charges, the balloon sticks to the wall.

Induction and polarization are the reasons lightning occurs. Air circulation causes clouds to polarize, with positive charges one top and negative charges on bottom. This causes the ground to do the same in response. The opposite charges between the cloud and the ground equalize, and energy is produced in the forms of light, heat, and sound (lightning).

Electric Fields and Electric Shielding

An electric field is an area around a charge that can influence (push or pull) another charge.
A drawing of an electric field has arrows, which indicate the direction in which positive charges would move and how powerful the electric field is (closer lines = stronger electric field).

Electric shields protect the charges inside of electric fields from being influenced by outside forces. This is done when charges distribute evenly about the charge, so the charge inside the area will feel no force, no matter its location. A prime example of electric shielding can be seen in electronics with metal cases. Metal cases serve as electric shields, so the contents will feel no force. 

Electric Potential, Electric Potential Difference, Capacitors

Electric Potential Difference, electromotive force, and voltage all mean the same thing. This means the difference in potential energy between two points. The greater the difference in charge between two objects, the greater the voltage. Voltage powers things. It is a measure of how much energy you can get out of one coulomb of charge (J/C or volts). You have probably seen appliances that say 100 v. This means that for every coulomb of charge produced, there are 120 joules in each coulomb. 

Formula: V= PE/C v or J/C

A capacitor is two oppositely charged metal plates attached to a power source. The charges transfer and energy builds up between the two plates. Capacitors are the things in cameras the cause a flash. The reason cameras take time between each flash is because the capacitor has to build up charge after each time it is used, before it can flash again. 

Ohm's Law, Types of Current, and Power

Current (I) is the flow of electrons in an electric circuit. It is measured in amperes (A). The equation for current is I = V/R (current equals voltage over resistance, also known as Ohm's law). Resistance is the hindrance of the flow of charges. When resistance is high, current is low, and vice versa. Resistance can be increased by making the current path longer and thinner, which makes it harder for electrons to move. 

There are 2 types of current: AC (alternating current) and DC (direct current). Direct current is the flow of charges in one direction, while alternating current is when electrons move back and forth about relatively fixed positions. AC can be found in generators, while DC is found in batteries.

Power is voltage times current (Power = VI) and is measured in watts. Energy = (power)(time). We can use these equations to calculate how much it would cost to run a 60 watt light bulb connected to a 120 volt source continuously for 1 month if it costs 10 cents per kilowatt hour. 

First, you must convert watts into kilowatts (move decimal 3 places to the left). This gives us .060 kw. There are 720 hours in a month (our time unit).

 energy = (power)(time)

            = .060 (720)

            = 43.2 kwh

Now we know there are 43.2 kWh when you run a 60 watt lightbulb for a month. When we multiply the number of kWh times the cost per kWh, we get $4.32. 

Parallel and Series Circuits

A circuit is any path along which electrons can flow. There are two different types of circuits: series and parallel. Series is a single pathway for electron flow and parallel has branches, each a separate path for electron flow. 

                                                     Series                                 Parallel

In a series circuit, the sum of resistance in a circuit is the sum of individual resistance along the pathway. If one device fails, the circuit is broken, stopping current and causing the other devices to stop working. 

In a parallel circuit each device operates independently and connects to the same two points of the circuit. A break in one path will not affect the other branches in a parallel circuit. The total current is the sum of the current in the parallel branches. As the number of branches in a parallel circuit increase, the resistance of the circuit decreases. This can cause overheating and fire. Fuses protect from fire by melting when the current in a parallel circuit is too large. It is connected to the beginning of the circuit, so when the fuse melts, all of the devices will cut off. 

Types of Current (AC and DC)

This source explains the difference between direct current and alternating current, as well as where you can find them in action.

Voltage Resource

This resource defines voltage in an electric field, and discusses the difference between electric potential and electric potential energy.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elevol.html

Mouse Trap Car Reflection

Speed: 4.56 seconds (to go 5 meters)
Place: 5th

Here is a video of our mousetrap car in action:

Here is a photo of our mousetrap car:

Here is a labeled diagram of our mousetrap car:


Each part used was light weight, so the car would have a greater acceleration (a=f/m).The CD wheels' mass were close to the axis of rotation, giving them a small rotational inertia and allowing them to spin quickly. Pens were used as axels, because they are smooth and have little friction, allowing the wheels to spin without hindrance. The balloon covering on the back wheels provided traction, allowing the wheels to push with a greater force on the floor and move forward. We used a long knitting needle attached to the mousetrap as our lever arm, which was connected to string wrapped around the back axel. When the mousetrap went of, the lever arm pulled the string which in turn rotated the axel, causing the car to move forward. Using a long lever arm allowed the car to travel a greater distance.

Physics of the Mousetrap Car

1.) How do Newton's laws apply to the performance of a car?

First Law: Objects in motion stay in motion, and objects at rest stay at rest, unless acted upon by an outside force.

This lets us know that in order for a car to move, there must be an external force to make it move. The force of the mousetrap being set of and the lever arm are what made our mousetrap car move.

Second Law: Acceleration = force/mass

This means that for a car to go quickly, it must have a small mass and a large force.

Third Law: For every action, there is an equal and opposite reaction.

This applies to how we can make the car move. For the car to move, it must exert a great enough force on the ground backward that it pushes the car forward.

2.) What are the two types of friction present, and how did you use these to your advantage? What problems did you encounter in terms of friction?

The two types of friction in our mousetrap car were rolling friction and sliding friction. Rolling friction was in the wheels pressing on the surface on which they were rolling. Sliding friction is in relation to the axles and the eye hooks, where the axel slide inside of their holding.

We used friction to our advantage to provide traction on the back wheels and start our car. We did not really face any friction-related problems.

3.) What factors did you take into account when choosing what wheels to use?

We decided that our wheels should have a small rotational inertia so they could spin quickly and be lightweight- also so they could spin quickly (a=f/m). CDs seemed like the perfect option. We used the same sized wheels on both axels, but the back wheel had balloons for traction. Reflecting, we probably should have chosen smaller front wheels for a greater acceleration.

4.) How does the conservation of energy relate to our car?

The kinetic and potential energy in our mousetrap car was in the lever arm, because it was the only part moving vertically. When the lever arm was pulled taught by winding the string, it had stored potential energy. Once the lever arm was let go, that potential energy decreased as kinetic energy increased.

5.) What was the length of your lever arm and how did it affect your car?

Our lever arm was 17cm long. By having a fairly long lever arm, our car was able to go a long distance (14m). This is because the lever arm is connected to the string which rotates the axel. The longer the lever arm, the longer distance it covers. The longer distance is covers, the more string it pulls, causing the axel to rotate more and the car to travel a farther distance.

6.) What were the roles of rotation in the functioning of your car?

We used wheels with their mass close to the axis of rotation, so, in turn, they had a small rotational inertia and a greater velocity. One way in which we could have improved our car would be to have had smaller front wheels with smaller rotational inertia and greater velocity. We wouldn't have changed our back wheels, because of the great function of our balloons and CDs for traction. Tangential speed did not play much of a role in the construction of our car.

7.) Why can't you calculate the amount of work the spring does on the car? Why can't you calculate the amount of potential energy stored and kinetic energy used in the car? Why can't you calculate the force exerted by the spring on the car?

1. You cannot calculate the work the spring does on the car, because the pull of the string is perpendicular to the spring. In order to calculate work, you would have to know the amount of force at each position as the lever arm moves, which we cannot do without a complicated formula.This is also why you can't calculate the force exerted by the spring. You cannot calculate potential and kinetic energy, because of this and also because energy could be produced in unused forms such as sound or heat.  

Reflection

1.) Final Design vs. Original Design

In our original design. we intended to use small bottle caps for front wheels and use the mousetrap as the base (no wooden platform). We were also going to use balloons to held the wheels on the axels and a pen for our lever arm. The small bottle caps were too wobbly, so we opted for CDs, and the wooden platform was too thin to hold the eye hooks that held the axels (we also just thought it would travel farther with a larger base). The balloons failed for holding the wheels, so we used hot glue instead, which was much more stable. The pen for a lever arm worked well and we passed the required 7 m on our first test run, but we thought a longer one would be more successful and help our car travel an even greater distance.

2.) Major problems and How They Were Solved

The greatest problem encountered was slightly uneven wheels, which hindered our car from going quickly. By readjusting with hot flue, we were able to make them more even and increase our speed. The other issue we faced was the wheels slightly catching on the glue holding the eye hooks. This slowed down our car. Sean readjusted the eye hooks and fixed the problem.

3.) What would you do differently in the future?

In the future I would focus more on speed rather than distance. While our car did go the farthest in the class (14m) it was right in the middle in regards to time. I would probably make the car smaller, especially in the wheels, which would decrease rotational inertia and increase velocity. I would also look for even lighter materials to increase acceleration (a=f/m).

Unit 5 Reflection

In this unit, I learned about…

Work and Power

Work is a transfer of energy and is responsible for power. The equation for work is, Work = Force x distance. Work is measured in Joules (J). For work to be done on an object, the force and distance must be parallel to one another.

In this image, the weight lifter is lifting a weight with a total mass of 50 kg. He is lifting the weight a distance of 2 meters. How do we solve for the work being done here? We already know the distance, so first, we must solve for the force.

Force = mass x gravity

          = 50 x 10

          = 500 N

Now that we know the force being used to lift the weight, we can find the work being done.

Work = Force x distance

          = 500 x 2

          = 1000 J

I mentioned earlier that work is responsible for power, but what is power? Power is how quickly work is done, or Power = work/time. Power is measured in Joule/seconds, other known as Watts (W). A Watt is 1 Joule over 1 second. So let's calculate the amount of power generated by the weight lifter. Suppose it took him 5 seconds to lift the weight.

Power = work/time

           = 1000/5

           = 200 W

Fun Fact! You've probably heard the term horsepower in reference to cars and other modes of transportation. 1 Horsepower actually equals 746 Watts!

Work and Kinetic Energy

Kinetic Energy is the energy of movement. The equation for Kinetic Energy is, KE = 1/2mv^2. How does KE relate to work? Work is the change in KE. By solving for the change in KE, you also solve for work. The equation for change in KE is, ∆KE = KEfinal - KEinitial

Let's solve some practice problems to better understand work and KE relationship.

1. A 20kg car accelerated from 20m/s to 30m/s in 5 seconds. In that time, it traveled 100m.

a. What was the change in energy the car experienced.

This problem is asking us to find the change in kinetic energy. To do this, we must first find the initial and final kinetic energies.

KEinitial = 1/2mv^2                 KEfinal = 1/2mv^2                   

               = 1/2 (20)(20^2)                      = 1/2 (20)(30^2)

               = 1/2 (20)(400)                        = 1/2 (20)(900)

               = 1/2 (8000)                             = 1/2 (18000)

               = 4000 J                                   = 9000 J

Once we solve for the initial and final KE, we can solve for ∆KE

∆KE = KEfinal - KEinitial

         = 9000 - 4000

         = 5000 J

Another example of this concept can be seen in my group's video. 

b. How much work was done?

Since work = ∆KE, we know that the work done is 5000 J.

2. A car is moving at come speed and requires 10m to stop. How many meters will it take to stop if the speed of the car is tripled? Why?

The first KE = 1/2mv^2

The second KE = 1/2m(3v^2)

                          = 9 (1/2mv^2)

Since the car's velocity is tripled and this number is squared, it's KE is 9 xs greater than its initial KE. 

Because the car's KE is 9 xs greater, it's work is also 9 xs greater. Work = force x distance, so the distance must be 9 xs greater. 

d = 9(10)

   = 90m

Conservation of Energy

Along with kinetic energy, there is something called potential energy. Potential energy is the energy of position. As long as an object is at some height, moving or not moving, it has potential energy. The equation for potential energy is, PE = mgh. Anytime an object moved, energy is conserved, meaning it doesn't change, even if something changes its movement. Energy is conserved, because anytime PE changes (increases or decreases), KE changes as well (increases or decreases in response). 

Take this swinging pendulum for instance. At the beginning of its swing, the ball has the creates PE, because it is at the greatest height. As the ball lowers and PE decreases, KE increases as the ball speeds up in response to the decreasing PE. KE is greatest at the bottom of the ball's swing. On the right side of the pendulum, the PE will be the same as it was in the beginning, because it is at the same height, and PE is the energy of position.

This conservation of energy suggests that the energy before will equal the energy after. Yet, we often hear about energy being lost. In these situations, energy isn't being lost, but is being produced in unused forms. Some of these forms include light, sound, and heat. One example of this is a car. Much of the energy from gasoline is produced as a vibration of the car, a rumbling of the engine, and the engine heating up. The amount of energy actually being used in a system is known as its efficiency. Percent efficiency is found by solving for work out/ work in.

Machines

Machines help us use our energy more efficiently by reducing the amount of force needed to move an object. In this unit, we addressed simple machines. A prime example of a simple machine is the inclined plane. As previously mentioned, work = F x d. The inclined plane, and all other simple machines, increase the distance an object moves, in turn decreasing the force needed to move it. Although the force exerted is decreases, the work will remain the same as it would have been lifting an object over a short distance. 

In this image, a man is pushing a 200 N object up an inclined plane of 12m. The ramp has a vertical height of 8m. The work that would be done if the man lifted the 200 N straight up 8m is called the workout. The work done pushing the weight up the 12m ramp is called the workin. We can use the following equation to solve for the amount of force needed to push the object up the ramp.

workin = work out

Fin x din = Fout x dout

F x 12 = 200 x 8

12F = 1600

F = 133.3 N

As you can see, the workout = the work in, but the force required to push the object up the ramp is smaller than the force required to lift it straight up. 

My problem solving skills, effort, and learning…

In this unit, I have completed all of my assignments on time and prepared well for all assessments. My group filmed a video about work and kinetic energy that was informative and went over what we covered in class on the subject. I finally learned how to embed videos in my blog, as can be seen above.  In this unit, I struggled with the conservation of energy, but coming into conference period clarified my confusion.

My goals for the next unit…

1) Continue turning in work on time

2) Continue preparing well for tests and quizzes

3) Make my group video more interesting

Simple Machine Resource

http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/simmac.html

This resource from hyper physics reiterates all of the information about machines we have discussed in class.

Power resource

http://www.youtube.com/watch?v=RpbxIG5HTf4

In this Khan Academy resource, power is discussed. They describe work and its relation to power. Instantaneous power is also discussed, but we have not talked about this in class as of yet.

Unit 4 Reflection

In this unit I learned about…

Rotational and Tangential Velocity

-Tangential velocity is the velocity of something moving along a circular path. The direction of motion is tangent to the circumference of the circle. Another word for tangential speed is linear speed. Tangential speed depends on the radial distance ( distance from the axis).
-Rotational velocity involves the number of rotations or revolutions around an axis per unit time. Rotational velocity is often measured in RPM (rotations per minute). Rotational speed will be the same at any distance from the axis of rotation.

An excellent situation in which to observe rotational and tangential velocity is on a merry go round. All of these children are traveling at the same rotational velocity, because they are making the same number of revolutions in a given time. However, the kids on the outer edge of the merry go round are moving at a faster tangential velocity than the kids towards the center of the merry go round. This is because they are covering a much larger distance in the same amount of time that the kids toward the inside are covering a very small distance. 

Rotational Inertia

Rotational inertia is the property of an object to resist changes in spinning. It depends on mass and its distribution. When the mass is closer to the axis of rotation it has less rotational inertia, so it speeds up, and when it is farther from the axis, it has more rotational inertia, so it slows down. So why does velocity change?

Conservation of Angular Momentum

We've learned about the conservation of momentum, ptotalbefore = ptotalafter;  p = mv; mvbefore = mvafter. This same same rule applies to rotational or angular momentum. In this case, rotational speed is velocity is conserved, so angular momentum before = angular momentum after. Angular momentum is based on two things: rotational inertia and rotational velocity, so  angular momentum = rotational inertia x rotational velocity; rotational inertia x rotational velocity = rotational inertia x rotational velocity.

In this video, we can see how the ice skater's angular momentum is conserved when she lessens her rotational inertia by bringing her arms in and increases her rotational velocity:
http://www.youtube.com/watch?v=AQLtcEAG9v0


Torque

Torque causes rotation. It is equal to force x lever arm. A lever arm is the distance from the axis of rotation. There are three things that affect torque: changing the force, changing the lever arm, or both. Torque is measured in Nm (Newton meters). The more torque an object has, the easier it is to rotate.
My group made a podcast about torque that further explains it implications:

http://www.youtube.com/watch?v=fOPdbmeks4A


Center of Mass/Gravity

All objects have an average position of their mass, called their center of mass. When gravity acts on that center of mass, it is called center of gravity. Center of gravity affects balance. When an object's center of gravity is inside of its base of support, it is less likely to fall over than when it center of gravity is outside of its base of support. When center of gravity is outside of the base of support, a lever arm is created, and the force of gravity gives the object torque, causing it to fall over.
This is exemplified in the following image:

The object with the smaller base of support will fall over because its center of gravity is outside of its base of support, while the large one will remain standing.

Centripetal/Centrifugal Force

Centripetal force is a center-seeking force that keeps objects going into a curve when rotating. Centrifugal force is a fictitious, fleeing force that causes an object to feel as if it is being flung outward.

One example of centripetal force is a satellite orbiting earth. One might ask, how does a satellite not end up being flung out of orbit or crashing into earth? Satellites are able to stay in earth's orbit, because they have the perfect velocity, so they don't cancel out the centripetal force (gravity) acting on them.

Below is a satellite orbiting the earth and a diagram of the forces and velocity.

Satellites orbit, because they have the force of gravity pulling them towards earth, but how do things like airplanes turning have a centripetal force? Their centripetal force is a resultant of Flift and Fweight.

This is also exemplified in car on a banked race track. The resulting centripetal force keeps the car on the racetrack. 

What I have found difficult about what I have studied is accepting that centrifugal force does not exist, but we feel something and call it centrifugal force and study it. I overcame these difficulties by listening carefully to class discussions and realizing that centrifugal force is a feeling, not an actual force.

My problem-solving skills, effort, and learning…

In this unit, I have completed all of my homework in a timely manner and participated in class. My group members and I created a helpful podcast about torque, and we worked well together. I found that I improved my blog posts, because I found a useful drawing app and learned how to properly link my video sources.

My goals for the next unit are to continue completing my work on time and improve my blog posts by providing more visual explanations and thorough descriptions.

Meter Stick Challenge

In step one, we discussed the meter stick's center of gravity, and the torque on the meter stick depending on where it was located on the table and how much weight was added to the end.

In step two, we decided a plan on how to solve for the mass of the meter stick using the stick and a 100g lead weight. We were not allowed to use a scale. We found the tipping point of the stick without a weight on it (this is its center of gravity), which was 49.5 cm. We also found its tipping point with the weight which was 71 cm. We realized that the torque and center of gravity would be the same with or without the weight, which allowed us to solve for the mass, because torque = force times lever arm. When we found the weight of the meter stick, we could convert it to mass using w = mg. 

In step 3, which we performed as a class, my partner Princess and I  found that our meter stick had a different center of gravity than the others, causing our mass to be different. In the corrected method, we first had to know that the counter clockwise torque is equal to the clockwise torque. Since torque = force times lever arm, we could calculate the weight of the meter stick by plugging in the proper units in their respective places. The lever arm when it was balanced with the weight was .3 m, but we didn't know the force (this would be what we solved for, and it was the clockwise torque). The lever arm with the weight with a counter clockwise torque was .2 m with force of .98 (on the center of gravity). Thus we were able to solve for force and mass. The resulting number must be multiplied by 2, because it equals only half the mass of the meter stick.

The following link is a depiction of the meter stick on the table with the mass:
https://docs.google.com/drawings/d/1JH6rNL7vy14oYnYhB5W25tmBF3VMLc3q7PvhRTb97h0/pub?w=960&h=720

How to solve for the mass of the meter stick:

1) counter clockwise torque = clockwise torque
    Force time lever arm = force times lever arm

2) w = mg
    w = .1 (9.8)
    w = 0.98 N

3) F(.3) = (.98)(.2)
    F(.3) = .196
    F = .65 N

4) w = mg
   .65 = m(9.8)
   .066 kg = m

          

Center of Mass and Torque

Torque Resource:

http://www.physics.uoguelph.ca/tutorials/torque/Q.torque.intro.html

This resource explains the relation between lever arm and force to create torque. It gives an example of torque when it explains how torque is involved when opening doors. It also tells us that in order for an object to rotate, the force must be perpendicular to the lever arm.

Center of Mass Resource:

http://www.youtube.com/watch?v=0-h1GUTKvCI#t=53

<iframe width="560" height="315" src="//www.youtube.com/embed/0-h1GUTKvCI" frameborder="0" allowfullscreen></iframe>

Hewitt-drew-it gives us an example of a dog on a plank hanging off of a cliff. He asks us how far the plank (and the dog) can hang off of the cliff, before falling over. He gives an equation to calculate this, and explains that the dog would fall if the plank overhung past the center of gravity of the plank and the  dog. He gives us the same question with a girl rather, than a dog, on the plank, showing that the center of gravity will be closer to the girl because of her greater weight.
He leaves us with a question: Two meter sticks are attached to create a ninety degree angle. Where should you place you finger on the sticks to balance them?

Angular Momentum Resource

Hewitt Drewit

http://www.youtube.com/watch?v=8I4ii1xEeG0

<iframe width="560" height="315" src="//www.youtube.com/embed/8I4ii1xEeG0" frameborder="0" allowfullscreen></iframe>

In this video, Hewitt tells us:

angular momentum = momentum times radial distance
angular momentum = mvr

An object or system of objects will maintain its angular momentum, unless acted upon by an external net torque.

gives us an example of this with planets and their moons

Shows a man spinning with weights pulling them out from his body (greater rotational inertia/ harder to spin)  and in closer to his body (smaller rotational inertia/easier to spin).

also gives example of ice skaters spinning in this same manner

if no external net torque acts on a rotating system, the angular momentum of that system remains constant (conservation of angular momentum)

Hewitt leaves us with a question: One is at an amusement park, in the middle of a turntable, that is set spinning freely. If one crawls towards the edge of the turntable, does its rotational rate increase, decrease, or remain the same? What physics principle supports your answer?