Idea 6of 6Builds onWarmth is where it wentHow fast you pay
The thermal tax
Two winches, two bills. Which machine is better?
Today you'll discover
- how to compare two machines that both get warm
- the share that counts, not the total
- the number that rates a machine
Think firstTwo winches, two bills: which keeps more?
Winch A banks 196 J of 240 J; winch B banks 90 of 100. Which is better?
Decide first, then press Next. Compare the first bar with the hollow bar.
An energy ledger for a winch lifting a crate: a hollow bar for the joules put in, a bar for the height energy banked, and a third bar for warmth. After a prediction, the banked bar is read against the hollow bar as a share, then the warmth bar as the share not kept. The last step asks the efficiency of a bulb.
See the whole ideathe big idea and the key word, in one place
The big idea
Efficiency is the useful share of what went in.
Easy to get wrongA low efficiency does not mean energy vanished. It means most of it became thermal energy. Count the warmth and the books always balance.
Key word
- efficiency
- useful energy out divided by energy in, usually as a percentage; never 100 % for a real machine
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?
- Find a machine's efficiency and say where the rest of the energy went.