Momentum
In physics there is a super special set of observations that rule over all of physics. They are Laws of Conservation. In chemistry you will meet two of them, ‘Conservation of Mass’ and ‘Conservation of Energy’. Today you meet the ‘Conservation of Momentum’.
Laws of Conservation are so important because they form the basis of nearly everything we know about science.
In your lab notebook: Define conservation.
Table of contents
Momentum
Momentum is quite simply the product (meaning multiply) of mass and velocity.
\[p=mv\](In physics momentum is represented with the letter p, m was already taken by mass.)
This means that the units of momentum is \(\frac{kg\times m}{s}\)
The easiest way to visualize momentum is to think of those times you were at the bowling ally. Rank the following on how hard they hit the pins (you can judge how hard by how much the pins go flying):
- A light ball thrown normal speed
- A heavy ball thrown normal speed
- A light ball thrown fast
- A heavy ball thrown fast
Light or heavy is relative to the mass, and how fast is relative to the velocity. Both more mass AND more speed make the impact when the ball hits the pins harder.
Conservation of Momentum
And now for the magic. The total momentum of a system (a collection of stuff, it can be anything really) IS CONSTANT (constant is what conserved means), IF there are no forces acting on the system.
Here the best example is another common game, pool. In pool, when you hit the balls you are applying a force, but the entire time after that, momentum is conserved ANY time two things interact. Question for you, is the pool table itself a part of the system?
If you want it to be, yes it is! What is in the system is your choice.
Don’t take our word for it though.
Activity - IIHS Momentum Bashing
To get a feel for momentum, go through the following actives created by the Insurance Institute for Highway Safety.
Activity - Vernier Momentum Lab
Now to put numbers to it.