Egg Drop

Recently, we had to create something that kept an egg completely safe and unharmed when it was dropped off about three and a half stories. Despite previous years' classes having a safe rate of about 50%, my class had a larger percentage safe. In fact, I believe only one or two groups had cracked eggs!

Anyway, for mine and Austin's project, we stuffed the inside of a box with various soft, cushion-y materials. The bottom of the box was lined with short, rectangular foam. On top of that, we place cylindric foam, staggering it so that it would be held in place by all the other foam cylinders. In the middle cylinder, we dug out a hold for the egg to rest in during the drop. Lastly, on top of the egg, we placed a bag of packing peanuts.

There were a lot of interesting designs, I liked the arial screw-like design by Joe and Jason. Anyway, we were really happy our egg survived. I took a really terrible video of it because I was unprepared when Austin dropped it. My finger tries to steal the show...

Crashing Cars

There are two types of collisions: elastic and inelastic. An elastic collision is a collision in which the objects involved bounce off of each other. Think of a being hit with a pillow during a pillow fight--that is an elastic collision. An inelastic collision is also known as a sticky collision. For this one, think of being hit with a snowball, or a massive ball of tape. Because both objects stick together, there is only one velocity for these collisions.

Previously we did an experiment that tested mass, velocity, and both collisions. My group personally had a lot of difficulty, but we managed to complete it. The elastic collision in which the more massive car hit the lighter car at rest was my personal favorite. It demonstrated how momentum is conserved. To make up for the lack of mass the heavier car had, the lighter car took on a faster speed.

Note: To find the velocity of the mass of an inelastic collision, the equation is as follows.

v = (p1 + p2)/(m1 + m2)

Impulse

Impulse is the change in momentum. Because impulse is the change in momentum, its symbol is a P, which stands for momentum, and a ∆ which indicates change. So ∆P represents impulse. The equation for change in momentum is: Fnet*∆T = ∆P. It can also be represented by P(o) - P.

If two objects, a rubber ball and a box, are thrown at a wall, the rubber ball will undergo a greater change in momentum than the box will. This is because the ball bounces back while the box hugs the wall and slides down. The ball bounces back towards the thrower this indicates the ball now has negative momentum. Suppose the ball, which bounces back the same speed in the opposite direction, and box are both 1 kg while the velocities are both 5 m/s to the right. The original momentum of the box is 1kg*5m/s =  5Ns. The final momentum of the box is 0Ns. The original momentum of the ball is 1kg*5kg = 5Ns. The final momentum is 1kg*-5m/s = -5Ns. Therefore, the impulse of the box is 5Ns - 0 = 5Ns, while the impulse of the ball is -5Ns - 5Ns = -10Ns.


Another thing to note: the longer the change in time is, the longer force can be applied at a low rate, as opposed to a short change in time with high force. The former is less painful than the latter. That is why it is better to land on a mattress than it is to land on cement when you jump off a high platform. (The picture is of my soft mattress that would probably not save anyone if they jumped off a high building, but would still reduce the impulse by at least a little bit.)

Linear Momentum

Momentum is mass multiplied by velocity so the SI unit is kg*m/s; there is no shorter way to write this unit. Mass is directly relational to momentum and inversely related to velocity. Therefore a fast but light ball might have the same momentum as a heavy but slow ball. In a more life-related example, if a deer from Nara, Japan takes a running start and attempts to tackle a gigantic but rather slow moving bear, the deer and bear may still have the same momentum if their m*v are the same.

Momentum is a vector because velocity is also a vector. Although there is a another sort of momentum besides linear, the other will always be specified as angular momentum. If unspecified, it is to be assumed that the material is referring to linear momentum.

(This formula is rather reminiscent of Newton's 2nd Law....)

Newton's 3rd Law

Philosophical or not, nearly everyone has heard of Newton's 3rd law:

 For every action (force) there is an equal and opposite reaction (force).

Yes, it can be applied to real life to reason that your little brother probably will plot revenge upon you for eating his ice cream, but it is mostly used for physics. That is, every time you push upon something with a force, that something pushes back on you with the same magnitude of force.

 For example, if Branson, the boy in the picture, pushed his seal plushie with a force of 10N, the seal, irregardless of being inanimate, pushes back on Branson with a force of 10N in the opposite direction. Thus, the force exerted both ways is the same. However, the accelerations of the seal and Branson would be different. This goes back to Newton's 2nd law, in which Fnet = m*a. Essentially, because Branson has a bigger mass than the plushie, he will accelerate slower than the plushie will. (Mass and acceleration are inversely related, remember?)