Idea 5of 5Builds onDraw the box firstWarmth is where it went
Where the missing joules go
A cart brakes. Where did its motion energy go?
Today you'll discover
- what braking does with the motion store
- why the brakes get hot
- how to find any 'lost' energy
Think firstA 2 kg cart at 14 m/s, braking
The cart stops. What happened to its 196 J of motion energy?
Decide first, then press Next. Watch the warmth bar take what the motion bar loses.
A ledger with a small drawing of a braking cart and three bars. After a prediction, the frames advance: the motion bar shrinks as the warmth bar grows, the total line staying put, until the cart is stopped and all the energy is warmth. The last step asks where a bouncing ball's missing energy went.
See the whole ideathe big idea and the key word, in one place
The big idea
Missing energy is thermal. Find it and the ledger balances.
Easy to get wrong'Lost' never means destroyed. It means the energy went somewhere less useful, almost always warmth spread thin.
About this modelThe bars move energy between stores; the total only changes when work is put in or taken out.
The bars move energy between stores; the total only changes when work is put in or taken out.
Ready to use it?
- Account for a described energy 'loss' by naming the thermal entry that balances the ledger.