Top Ten Ways of Living in a Dorm

Top Ten Ways of Living in a Dorm

1) Levering your door so you can level the amount of dust in your room.

If you want to open your room so you can bring the vacuum inside, you need to prop open the door. To do that you need to create a torque -- the force that causes rotation. To prevent the door from closing again, you will need to create a large lever arm by putting the door stopper at the end of the door (closer to the handle) so it will be farther from the axis of rotation. *A lever arm is the perpendicular distance from the axis of rotation to where the force is applied* A large lever arm will prevent you from needing a large force [torque = (force)(lever arm)] such as needing to put an object in front of the door to keep it open. Now you can easily vacuum your room!

2) Friction! You've done it again!

When you want to roll a bouncy ball to your friend down the hall, it doesn't always make it to their room. This is because Newton's 1st Law states, "things in motion will stay in motion and things at rest will stay at rest unless acted upon by an outside force," and when friction (the outside force) acts on the ball it won't make it all the way to your friend's room. The ball would make it all the way to your friend's room if the ground was frictionless. 

3) Bad water pressure.. 

Newton's 2nd Law states a = f/m. If the shower head isn't pushing out the water with a large amount of force then the water won't have a large acceleration, because acceleration is directly proportional to force. To have better water pressure the water needs more acceleration when coming out of the water head, thus the water head needs to push the water out with a larger force. 

Good shower heads use Newton's 2nd Law to their advantage.. 

4) Prom struggles. 

The dorm is on a parallel circuit, so each room is individually sourced. When a device is added to the circuit the current goes up and the resistance goes down. So.. when a bunch of devices are added to the circuit the current gets really high and breaks the fuse. 

A fuse stops the current flow when it (the fuse) gets to be a certain degree of heat. When the current gets too high the fuse will burn breaking the fuse, so that the wires don't cause a fire. A fuse is only added to a parallel circuit or a series/parallel combined circuit. The fuse will break if too much current is drawn from the wall, and this will cut the current to all devices to prevent fires, because too much current causes heat which is dangerous. 

5) When after study hall you have way too much energy and start to spin around and around, but you can't quite seem to spin fast enough to satisfy yourself. How would you make yourself spin faster?

Angular momentum = (rotational inertia)(rotational velocity) so when you want a large rotational velocity you need a small rotational inertia. To get a smaller rotational inertia than you already have, you can bring your arms in closer to your body because that puts your mass closer to your axis of rotation, which decreases your rotational inertia and increases your rotational velocity, which will make you spin faster. 

Conservation of angular momentum says that angular momentum before = angular momentum after,

because angular momentum is always conserved. 

(rotational inertia)(rotational velocity) = (rotational inertia)(rotational velocity)

so...

(ROTATIONAL INERTIA)(rotational velocity) = (rotational inertia)(ROTATIONAL VELOCITY)

6) When you and your friends are goofing around in the hallway, you jump on your best friend's back. You aren't sturdy on her back and fall off. Why is that?

All objects have an average position of all their mass -- center of mass. When the center of mass goes past the base of support, the object will fall over. When you're on your friend's back, if you aren't over her base of support, then you will create a torque and will fall over. A way your friend could keep you on her back would be for her to bend her legs, because that will lower her center of gravity. When you have a higher center of gravity, you are more likely to create a torque and will fall over easier. When you're on her back, the best thing for her to do is to make herself low to the ground and wide, because that will widen her base of support and make her less likely to fall over.

7) When you take your clothes out of the washer and wonder why they're still soaking wet. 

Centripetal force is the force that makes a body follow a curved path. In a washing machine the clothes have a centripetal force and the water has a tangential velocity. Within the washer are little holes on the inside that allows water to come out when the clothes are done being washed. The water is able to come through the holes, because it continues to move in a straight line with a tangential velocity (no centripetal force). If there were no holes the water would have a centripetal force and would stay inside the washer. When you take your clothes out of the washer right after the washing cycle has finished, all of the water has not come out of the holes yet, so they're still going to be soaking wet. 

8) When you're moving out for the summer, you're trying to push a box packed full with stuff, but it won't move. 

Equilibrium is reached when an object is either at rest or moving with constant velocity. If you're pushing the box with 150N, but there is 150N of friction between the ground and the box, the box isn't going to move because 150N - 150N = 0N and equilibrium is reached at 0N. To move the box you will need your friend's help so there will be a larger force on the box than the force of friction. Even if your friend only adds 1N of force, that is still 151N vs. 150N, so the box will now move. 

9) You have a lot of homework to do so you go to the dining hall, make a sandwich, and bring it back to your room to finish studying. You now have a delicious peanut butter and jelly sandwich sitting on your desk. What forces are acting on the sandwich? (ignore plate in picture)

According to Newton's 3rd Law, "every action has an equal and opposite reaction."

1) Sandwich pulls earth up <--> earth pulls sandwich down

2) Table pushes sandwich up <--> sandwich pushes table down

10) Your hall is throwing a surprise birthday party. Your job is to blow up all the balloons, but someone runs up to you, takes a ballon, rubs it on your hair, and sticks it to the wall. How did that happen?

The balloon sticks to the wall by induction. When the ballon is rubbed on your hair it steals electrons from your hair, making your hair positive and the balloon negative. The negative charge of the ballon is attracted to the positive charge of the wall, and the other side of the wall (the negative charge of the wall) is repelled from the negative charge of the balloon. This makes the wall polarized and Coulomb's Law says F = kq^1q^2/d^2 so since the opposite charges are closer in distance than the like/repulsive charges, their force is stronger than the like/repulsive charges. Thus the balloon sticks to the wall. 

Wind Turbine

Building a Wind Turbine

Materials I used to build my wind turbine:
1) cardboard - the base and the generator box
2) copper wire - to allow current to flow
3) hot glue - glue boxes together
4) a metal rod - the axle that allows the magnets to spin as the wings spin
5) 8 small magnets - creates a magnetic field

Electromagnetic induction is when a coil of wire is brought close to a magnet, inducing a voltage, and then causing a current.

Newton's 1st Law: An object at rest will stay at rest and an object in motion will stay in motion unless acted upon by an outside force.
--> The wings stay at rest until the fan made them spin.

Newton's 2nd Law: a = f/m
--> the more force (wind) the fan applied, the faster the wings spun, and the more mass the wings had the slower they went.

Newton's 3rd Law: Every action has an equal and opposite reaction.
--> Wind pushed wings -- wings pushed wind

When the wind blows the wings it creates a torque, causing the wings to spin and thus causing the magnets to spin.

Motors convert mechanical energy into electrical energy, so when the wings spin energy is created from electromagnetic induction.

This is our model. We used a tall cardboard box as the base, so the wings could spin easily without hitting the ground.

The smaller box on top of the base is our generator. Copper wire is coiled around the box on both sides. We had to be careful to wrap both coils in the same direction, so both currents would be going in the same direction.

We stuck a metal rod through the generator box for two purposes...

1) To allow the magnets something to stick on to. 

2) To attach the wings on the ends, so when they spun the magnets would also spin thus inducing a voltage.

Inside the box are 8 small magnet - 4 on each side of the rod. Electrical tape is wrapped around them to make them stay close to each other. We want to have the same poles facing each other, so that the same poles are facing outward to create a magnetic field.

*If both north and south are facing outward, then there are two poles creating a magnetic field, which would mess up the electromagnetic induction process.

Same poles repel each other, so there is a strong repulsion when same poles are facing each other; thus we wrapped the magnets in electrical tape so it would be harder for them to get away from each other. This way the magnets can spin freely - without someone holding them together - when the axle spins as a result of the wings spinning.



The fan spins the blades, which spins the magnets in result and this changes the magnetic field of the wire. This changing of b induces a voltage and causes a current to flow resulting in a generation of electricity.

We generated .008V and .008A but we were not able to light the lightbulb, because we didn't generate enough voltage.

Factors that affect the amount of voltage induced:
1) Having both coils of copper wire wrapped in the same direction, so the current flows in the same direction in both coils.
2) Having the same poles facing outward, so they'll create a magnetic field.

One issue we ran into was friction. When our magnets spun, as a result of the wings spinning, they would rub up against the walls of the box, thus slowing down the speed of the wings.

If I were to do this project again I would make a bigger generator box, because when we needed to rearrange the magnets - when we learned that same poles need to be facing outwards - it was difficult to move them with the box being so small. I also recommend coiling the wire around your generator box as you're uncoiling it from it's original roll, because the wire gets easily tangled.

Unit 6 Summary

Magnetism 

Source of all magnetism = moving charges 

domain - a cluster of electrons all spinning in the same direction 

*Not magnetized if the domains aren't all facing the same direction.

Charges moving in a wire (AC current)

 Magnetic field lines go towards north, around the magnet and back towards south

Field lines going in the same direction will attract the magnets together.

Field lines going in opposite directions will repulse the magnets from each other.

Why does a paper clip stick to a magnet?

A domain is a cluster of electrons that are spinning in the same direction. The domains in a paper clip are randomly aligned. The magnet has a magnetic field, and when the magnet is close to the paper clip the domains of the paper clip align to match the magnetic field lines of the magnet. The paper clip now has a north and a south pole, and since opposite poles attract the north pole of the paper clip is attracted to the south pole of the magnet, and thus the paper clip sticks to the magnet. 

compass - a magnet that is free to move and respond to a magnetic field. 

*A compass' needle only moves when it encounters a different magnetic field, and it will align with that magnetic field.

Magnetic fields can exert forces on other things (usually magnets) with magnetic fields. 

*symbol for magnetic field = b

Motors 

A motor relies on current bearing wires and magnets. 

How a motor works = a current carrying wire feels a force in a magnetic field and causes a torque 

All moving charges feel a force in a magnetic field if their velocity is moving perpendicular to the magnetic field. If it's moving parallel it won't feel a force, which is how things enter our atmosphere. 

*This is why the equator is generally shielded from cosmic rays entering, and the northern countries aren't. 

Current is moving perpendicular to the magnetic field (the charges have a force from the magnetic's magnetic field).

Electromagnetic Induction

Electromagnets have a current carrying wire that has a magnetic field. The domains of an unmagnetized object can align with that field and then have a magnetic field of its own. 

Electromagnetic induction - when you bring a coil of wire near a magnet, the magnetic field of the coil will change. The induces a voltage (from electromagnetic difference) and that causes a current. 

*Used in traffic lights, airport metal detectors, credit card machines, generators, transformers, etc.

*The # of loops is directly proportional to the amount to current (2 loops = 2x current). The greater the number of loops, the greater the induced voltage. 

Voltage is caused, or induced, by the relative motion between a wire and a magnetic field. The magnetic field of a magnet moves near a stationary conductor or vise versa - the conductor moves near a stationary magnetic field. 

1) move the loop near a magnet

2) move the magnet near a loop

3) change the current in a nearby loop 

The amount of current produced by electromagnetic induction depends not only on the induced voltage, but also on the resistance of the coil and the circuit to which it's connected. 

Faraday's Law: The induced voltage in a coil is proportional to the product of its number of loops and the rate of which the magnetic field changes within the loops. 

How do credit card machines work? 

Credit card machines work by electromagnetic induction, which is when you bring a coil of wire near a magnet, the magnetic field of the coil will change. The induces a voltage (from electromagnetic difference) and that causes a current. In the machine are several loops of wire, and when the series of magnets passes through the coil a voltage is induced, which causes a current. This current acts as a signal to approve/decline the card. 

Transformers

Transformers use electromagnetic induction to either step-up or step-down the voltage. 

The primary (1) is connected to a power source.

*more loops = more V induced

*more length = more resistance

As the I changes direction the magnetic field in the primary constantly changes direction as well, and that changing b of the primary induces a voltage in the secondary and will cause a current in the secondary. 

You can't use DC current in a transformer and have to use AC current, because you need a constantly changing magnetic field, to induce the voltage thus to cause a current, so you need an alternating current. 

Generators

Generators rely on turning objects. 

1) magnets

2) coils of wire

When one end of magnet is repeatedly plunged into and back out of a coil of wire, the direction of the induced voltage alternates (AC current).

Both motors and generators use coils of wire and magnets to transform energy from one form to another, but their techniques are different. 

A motor transforms electrical energy into mechanical energy. It uses a current carrying wire that feels a force in a magnetic field and that force causes a torque.

A generator transforms mechanical energy into electrical energy. It relies on electromagnetic induction: a spinning wire over a magnet or vice versa. This creates a charge in magnetic field, induces a voltage and then causes a current.