Second Law of Motion: Momentum is conserved. Momentum can be defined as mass in motion. Something must be moving to have momentum. Momentum is how hard it is to get something to stop or to change directions. A moving train has a whole lot of momentum. A moving ping pong ball does not. You can easily stop a ping pong ball, even at high speeds. It is difficult, however, to stop a train even at low speeds.
Materials: garden hose connected to a water faucet
[am4show have='p8;p9;p10;p37;p72;p92;' guest_error='Guest error message' user_error='User error message' ] Place your thumb partway over the end of a garden hose. The water shoots out faster because the same amount of “stuff” has to pass through the exit. When the exit area decreases, less mass can pass through at one time, so the velocity increases.
Mathematically, momentum is mass times velocity, or Momentum=mv.
One of the basic laws of the universe is the conservation of momentum. When objects smack into each other, the momentum that both objects have after the collision, is equal to the amount of momentum the objects had before the crash.
The next video shows you how once the two balls hit the ground, all the larger ball’s momentum transferred to the smaller ball (plus the smaller ball had its own momentum, too!) and thus the smaller ball goes zooming to the sky.
Download Student Worksheet & Exercises
Do you see how using a massive object as the lower ball works to your advantage here? What if you shrink the smaller ball even more, to say bouncy-ball size? Momentum is mass times by velocity, and since you aren’t going to change the velocity much (unless you try this from the roof, which has its own issues), it’s the mass that you can really play around with to get the biggest change in your results. So for momentum to be conserved, after impact, the top ball had to have a much greater velocity to compensate for the lower ball ’s velocity going to zero.
Find out more about this key principle in Unit 1 and Unit 2.
Advanced students: Download your Momentum lab here.
Exercises
Materials: garden hose connected to a water faucet
[am4show have='p8;p9;p10;p37;p72;p92;' guest_error='Guest error message' user_error='User error message' ] Place your thumb partway over the end of a garden hose. The water shoots out faster because the same amount of “stuff” has to pass through the exit. When the exit area decreases, less mass can pass through at one time, so the velocity increases.
Mathematically, momentum is mass times velocity, or Momentum=mv.
One of the basic laws of the universe is the conservation of momentum. When objects smack into each other, the momentum that both objects have after the collision, is equal to the amount of momentum the objects had before the crash.
Download Student Worksheet & Exercises
Do you see how using a massive object as the lower ball works to your advantage here? What if you shrink the smaller ball even more, to say bouncy-ball size? Momentum is mass times by velocity, and since you aren’t going to change the velocity much (unless you try this from the roof, which has its own issues), it’s the mass that you can really play around with to get the biggest change in your results. So for momentum to be conserved, after impact, the top ball had to have a much greater velocity to compensate for the lower ball ’s velocity going to zero.
Find out more about this key principle in Unit 1 and Unit 2.
Advanced students: Download your Momentum lab here.
Exercises
- What concept does Newton’s Second Law of Motion deal with?
- What is momentum?