This super fun activity for ages 5 and up helps students gain an intuitive feel for momentum.
What you’ll need:
- Hall’s Car Pair (PH0351APL)
- Straight toy-car track (Hot Wheels, for example) – about 4 feet length minimum.
- Garden rocks or weight set (PH0037ASS)
- Kitchen Measuring Scale
Setting up the track::
- Lay out the track on the floor. Put the Hall’s Cars on the track with loops facing each other. (They won’t fit, but you just need two wheels on the track).
- Line the cars up for a direct collision with the wheels on the edge of the track. (This will keep them going straight).
Procedure:
Investigation 1:
- Gently push the cars toward each other at the same speed. What happens?
- Now fill one car with as much weight as you can and repeat. What happens?
The heavier car, pushed at the same speed as the lighter car, carries much more momentum. Some of that momentum is transferred to the lighter car.
Can you guess how fast the lighter car moves after the collision compared to its initial speed?
A. About the same speed.
B. About twice as fast.
C. About three times as fast.
If you guessed about three times as fast you’d be right.
Investigation 2:
- Now put the empty car in the middle of the track and send the heavy car toward it. What happens?
Can you guess how fast the lighter car moves after the collision compared to its initial speed?
A. About the same speed.
B. About twice as fast.
C. About three times as fast.
If you guessed about twice as fast you’d be right.
What happens to the heavy car in the above interactions? Does its speed change very much?
Think about it - an object with more momentum is less susceptible to changes in speed. How easy is it to stop a toy train? How easy is it to stop a full-size train?
Investigation 3.
- Now make both cars empty again. Put one in the middle and launch the other toward it. What happens now?
The momentum from the first car is completely transferred to the second car! Does this depend on the speed of the first car?
This is a special case that only happens when the masses match!
Bonus Investigation:
- Try to add mass to the stationary car until both cars leave the crash at the same speed in opposite directions.
If you’re able to make this happen, use the kitchen scale to measure the ratio of the loaded Hall’s Cars. Turns out the ratio will be about 3:1. Does this depend on the speed of the lighter car?
