Unit 4 reflection!

Unit 4 mainly talked about momentum and impulse. We stablished that momentum is inertia in motion and is equal to the mass times the velocity of the body (P = mv). The product of the force acting on an object and the time which acts its called impulse (J = f Δt). Impulse is also the result of change in momentum (J = ΔP). Momentum and impulse can explain a lot of everyday life situation. For example: why is it better for a karate fighter to exert a force for a short period of time when breaking a brick? The answer to that questions seems like it would be prety easy, but... in order two variables in an equation, the other variable needs to be proven constant. In the equation J = f Δt, in order to prove that time determines the force necessary to achieve a certain impulse, the impulse needs to be proven constant. To prove impulse is constant you need to state that regardless of the time, (continuing with the karate example) the hand of the fighter is moving and comes to a stop therefore since the mass is obviously the same and P = mv, the change in impulse is the same (ΔP = Pfinal - Pinitial). We stated before that J = ΔP therefore J is constant! To continue to answer the question, you should now state that J is also J = fΔt.  Because of the last equation is possible to afirm that the smallest the time of contact the greater the force will be in order to achieve the constant J. Since to break a brick you need the greatest force possible, the time of contact should be as small as possible.
Still don't understand? Try watching this explanation

  After learning about the relationship of momentum and impulse we talked about bouncing. 

To explain bouncing, my class watched a demonstration of two identical balls in direction of a wood block each. One of the ball sticks and the other one bounces. The question was which one of the balls will knock the wood block over? The answer to that question was the bouncing ball! The reason why the bouncing ball knocks the block over is because there is not only one force acting on that block. Because of Newton's third law, we know that for every action there is an equal and opposite direction therefore ball pushes block, block pushes ball in both cases. The bouncing ball not only causes that force, the ball will bounce on the block adding another force taht causes the block to fall over.

After talking about bouncing, we talked about concervation of momentum. Conservation of momentum is apliable when there is a system. Conservation of momentum is represented by the equation: 
P before = P after . When dealing with collisions conservation of momentum is verry helpful. We learned that ther are two different types of collisions:

Elastic collision:
A collision in which colliding objects rebound wothout lasting deformation or the generation of heat.

Inelastic Collisions:
A collision in wich colliding objects become distorted, generate heat, and possibly stick together.

We learned that because of the concept of collision and conservation of momentum is possible to find out many things about the colliding objects. If for example you know the masses and the velocity of the objects before the collision and they stick together, or one object is at rest, it only takes a few steps to find out  the velocity of those objects after the collision by using the conservation of law affirmation.

Reflection:
The hardest part of this unit was writing out a complete answer for a problem like the karate one. It became easier to remember to include all the information neeeded after we  answered homework questions on the board and got a chance to learn with each others mistake.