Emrys slides a pan of cold dough into a hot oven. Minutes later the dough is warm through.
Energy moved from the oven to the dough. Physics has one word for energy moved that way, and the word is easy to misuse. This lesson pins it down.
The oven air is hotter than the dough. Because of that temperature difference, energy transfers from the oven air to the dough.
Heat is a transfer that happens, not a substance an object contains.
The dough does not fill up with a fluid called heat. What the dough gains, and has, is thermal energy.
A hot object has thermal energy. Heat is the transfer of some of that energy to a colder object.
No temperature difference means no heat: two pans at the same temperature, touching, transfer no heat to each other.
In earlier grades, you saw energy move from hot things to cold things. The precise claim this lesson adds is what heat is: the transfer itself, never stuff stored inside an object.
A cold metal spoon rests in hot cocoa. Where is the heat in this scene?
The cocoa is hotter than the spoon, so energy transfers from the cocoa to the spoon.
That transfer is the heat.
What the cocoa has, and what the spoon is gaining, is thermal energy.
The heat is the transfer from the cocoa to the spoon, driven by their temperature difference. Neither object contains heat.
Two water bottles, both at room temperature, touch inside a backpack. How much heat is transferred between them?
Heat needs a temperature difference.
The bottles' temperatures are equal, so no difference drives a transfer.
No heat is transferred: 0 J.
Energy is moving from a hot grill plate into a cold burger pressed on it. What makes this transfer count as heat?
Birta says: 'A hot brick has a store of heat inside it, like a fluid it can pour out.' Is Birta correct?
Ivo says: 'Two pans at the same temperature, touching, transfer no heat to each other.' Is Ivo correct?
Which statement about heat is correct?
A sealed pouch of cold sauce sits in hot water. Heat is transferred to the sauce for a while, and then the transfer stops. Why does it stop?
A hot pancake sits on a cold plate. Which sentence uses the word heat correctly?