Boxi Learn › Physics › Stage 4 · Systems and Argument
Who pushes harder in a crash?
PHY-2 Energy and momentum are conservedPHY-1 A force changes motion, it does not keep it goingX-2 Evidence outweighs opinion
What many people think
In a crash the bigger object pushes harder.
The idea
Both carts push each other equally hard for the same time, so the total momentum is the same before and after, even when energy turns into heat.
Explain it
A friend says “the truck hit the car harder than the car hit the truck”. Using the words “force”, “time” and “momentum”, explain what is true and why the car’s passengers still feel more.
Try at home
Hold two equal bathroom scales face to face and push them together with a friend: compare the two readings while you push gently, then hard. Then roll a heavy ball into a light one on a smooth floor and watch which one changes speed more.