Unit 4 Reflection

This unit was not incredibly difficult.  We started off learning about momentum.  We were prompted with the question, "Can a skateboard, which has very little mass, have more momentum than a big 18-wheeler?"  To answer this question we were taught the equation for momentum.  It is very simple: P=mv.  Using this equation, it can be inferred that if the skateboard picks up more velocity than the truck, it will actually have more momentum.  
It is mind boggling, but I found something else with a low mass and a very high momentum:

This car is very small, but it can reach dangerous speeds-so dangerous that the makers actually warn that the car is "only for experts".  During class, we actually defined momentum as "inertia in motion".  Here is an example problem:

If a bowling ball has a mass of 12 kg, and rolls at a speed of 5 m/s, what is its momentum?
Answer: P=mv, so P=12(5), P=60 kgm/s.

We then transitioned to impulse.  Impulse is the term used to describe a change in momentum.  The equation for impulse is J=f(delta)t.

Throughout the unit we used a set of very similar questions to apply this knowledge.  They were worded as follows: Why do we need airbags?  Why do padded floors help protect gymnasts?  Why is it better to roll with the punches?  These questions are all answered the exact same way.  The most important thing to remember is to include all equations and back up each assertion with an equation.  To answer these questions, you need to first state that p=mv, and the object the object will change velocity, therefore the momentum will change.  You then state that J=F(change in time).  Since J is constant, if the time increases the force will decrease.  These questions were difficult for me at first, but then I started to get used to the pattern.  These questions relate the most to the real world.  For instance, if you ever decide to be a boxer, you will know how to make sure you receive minimal pain when being punched.

Finally, we discussed conservation of momentum.  The equation for conservation of momentum is: mvbefore=mvafter.  The law of conservation of momentum states that momentum will stay constant before and after a collision.  For instance, if a moving car hits a stationary car and the two stick together, the momentum of the system will equal the momentum of the moving car before the collision (we disregard the other car because it had no velocity, and no momentum).

This is a great video on conservation of momentum:

One thing I found to be very difficult about this unit was knowing which formulas to use for each question.  Thus, my problem solving skills declined.  However, Ms. Cianculli helped our class one day, and she explained a few problems very clearly, and I was able to grasp these ideas a little better.