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:
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.
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