Top Ten Ways of Living in a Dorm
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.
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