Physics grade 4?
If you wanted to open the jar of jam but the lid was too tightly capped , to make it easier to open you would pour hot water on the metal lid. Why does it work?
If the lid is made of plastic , will it work just as well, ? Why?
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heat energy makes any form of matter expand, (exept rubber)
by pouring hot water over the plastic lid, the plastic in the plastic lid expands slightly, allowing you to easily pull it off....
AND EAT ALL THE GOODIES INSIDE!!!
Materials expand when heated, so pouring hot water on the lid causes it to expand a little, making it easy to open. Metal lids work best, because metal is a good conductor of heat, so the lid heats up and expands more quickly.
It will also work on a plastic lid, but not as well as plastic is a poorer conductor of heat.
Wouldn't that be Science, not Physics?
If the jar was cold, the lid would be slightly frozen on the jar. By pouring hot water on it, you melt the ice, making the cap come off easier.
You need to be more specific.