The Top Ten Things of Physics

Inertia

an object's non-wanting to change states (is measured by an object's mass). An example of inertia is the tablecloth trick

Ohm's Law

Ohm's law has to do with resistance. V=IR is the equation for Ohm's law. V= voltage, I= current, and R= resistance.

Units for V, I and R

Newton's 1st Law

An object at rest tends to stay at rest and an object in motion tends to stay in motion unless acted upon by an outside force.

Newton's 2nd Law

 acceleration is directly proportional to force, and is inversely proportional to mass. F=ma

Newton's 3rd Law

 “every action has an equal and opposite reaction.”

Action Reaction Pair: Hammer pushes nail down, Nail pushes hammer up

Speed and Velocity

You can accelerate while keeping the same speed only when going in a circle without changing speed. Cannot have changing speed and have constant velocity. Difference between velocity and speed is that v requires a specific direction and speed does not

Work/Power

For work to happen, force and distance must be PARALLEL!!
Example problem:

Equation: Work=(force)(distance)

Units: Joules (J)

Equation: Power=work/time

Units: Watts

If a 600N person walks up stairs that are 4 meters high, how much work is done?

Work=F*d

Work=600N*4m

Work=2400J

When is there more work? When a person goes up the stairs to third or when the elevator carries them to third?

The work required is the same. The upward force against gravity (or weight) is the same, and the distance that is parallel to that force (height) is the same, therefore work is the same. Horizontal distance does not matter because it is perpendicular to the upward force, and therefore contributes nothing to the work done.

When considering work, only the height matters.

Work happens to an object when force is exerted on that object over a distance. The equation for work is work=force*time, and it is measured in m/s or Joules. For there to be work, the force and distance must be parallel. In this example, the person's wright, or force, is vertical, and therefore for there to be work, the distance must be vertical as well. Work does not happen when the distance is perpendicular to the force, or when there is no distance.

If the force of the person is 4N, and the staircase is 15m tall, how much work will there be? 

work=force*distance

        = 4N*15m

work= 60 Joules

Power is how quickly work is done. The equation for power is Power=(work)/(time) and is measured in Watts.

If it takes the person 10 seconds to reach the top, how much power is exerted?

Power=(work)/(time)

=60J/10s

Power=6 Watts

Coulomb's Law

Coulomb's law states that the electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects.

Torque 

Torque is a measure of how much a force acting on an object causes that object to rotate. Torque is equal to the force multiplied by the lever arm. Torque IS NOT equivalent to force! Lever arm is the distance from the axis to the center of gravity. 

Conservation of Momentum

Individual objects can change their momentum, but systems cannot

Ptotal before=Ptotal after

Together in the Beginning:

m_av_a+m_bv_b = m_av_a+m_bv_b

Together in the Ending:

m_av_a+m_bv_b=m_a+bv_ab

Generator

Magnetism is caused by moving charges. By moving the magnets in circles in between the coils of wire, the change in magnetic field needed to induce voltage in the coils is created. This results in AC output. This change of mechanical energy into electric energy is what makes the wind turbine a generator. Notice that I said "generator" and not "motor." There is a distinct difference between these two: motors take electrical energy and turn it into mechanical, while generators take mechanical energy and turn it into electrical. 

Materials used:

4 90-degree elbow PVC fittings, 3 PVC T-fittings ~5 ft. of straight PVC pipe, One large T-fitting with a diameter of at least 2 in. This will house the coils and shaft. At least 2 dowels, 3/8" diameter each (or whatever size you can drill a hole for) 2 PVC end-caps for the generator housing. Solid. You'll drill appropriately sized holes depending on your dowel size later. A small wooden wheel, like you might see on a toy car, to serve as the hub. This is what the propeller blades will be attached to on the outside of the pipe. Several small wooden disks to put your magnets on to. At least 12' of copper wire Some cardboard or other light-weight material to build your blades with. Electric tape, hot glue, sharpies, and any other small supplies you might need when building. Various power tools, most importantly a drill, and a voltmeter.

Side shot of our generator

Here is the inside shot of our generator

 Here is a sketch of the magnet placement and orientation, coils

Here is a sketch of our turbine/generator

On our first try, our generator induced a voltage, so not much difficulty was had there. However, making the generator was more difficult. At one point, someone took our 'magnet wheel' so we had to make a whole new rod, which was more annoying than hard, but it made us take longer to create the generator. We also had trouble putting the generator together. We knew what it had to look like, but we tended to make things more difficult for ourselves by focusing on potential problems that we had not yet encountered. I think it would have gone a lot faster if we had just tested it a bunch before deciding if something was a problem or not.

1.     Resistance

On the wire connecting the coil to the alligator clips

Friction inside the rotating piece

2.     Magnet Placement

The closer the magnet without touching the coil the higher voltage output induced

3.     Coil Strength

The thicker the coil, the stronger the coil. 

The thicker your coil is the higher voltage output it induces.

Motor

Function of each material:

• Loop of Copper wire: Conductor and turbine
• Battery: Provides current flow that allows the magnetic force to influence the wire loop.
• Magnet: provides a magnetic field and therefore a force on the current running through the wire, causing it to spin from the torque applied to the loop.
• Paper clips: hold up the motor coil and allow the current to flow from the battery to the coil.
• Rubber bands/electrical tape: holds the motor together
• Wooden Block: acts as a support for the motor

Why we scraped the armature in a specific way:

We needed the motor to be spinning in a constant direction for it to work, instead of a back-and-forth motion. In order to accomplish this, we had to scrape the wire. We needed the current to flow only when the loop was oriented in a specific way, and not the other. In order to make the motor run properly, we needed the current to flow while the loop was turning in one direction. This would need to happen without causing the loop to turn in the other direction because this would be counter productive.

Why the motor runs:

The motor was able to turn because of the magnetic pull created by the magnet. All magnetism is caused by moving charges. Because of this, in a magnetic field, moving charges are affected by the magnetic force; if the charges are moving perpendicularly to the field, the force is even greater. Therefore, since the motor coil is oriented perpendicularly to the magnet (the coil must be vertical), the magnetic force acting on the charges moving through it is even greater, and the force (which has an upward direction) also acts on the coil itself. Since the sides of the wire are pushed in opposite directions, the wire rotates. When the wire flips and the current is still going in different directions, the magnetic field continues to act on it unless affected by an outside force.

What the motor can be used for:

Unfortunately this motor cannot be used for anything, for it only has enough force to overcome its own friction.  This can however, potentially be used to:

• Entertain your friends
• Impress your physics teacher (**hint**)
• Look cool