Heat and the First Law

The arrow pointing from the hot tea to the cool tea indicates the passage of time.
When a hot cup of tea is left in a room in contact with the ambient air, we know that eventually the tea cools and the air warms until the temperature of the cup of tea and the surrounding air are the same.
The 1st Law tells us that the decrease in the internal energy of the cup of tea is equal to the increase in the internal energy of the surrounding air.
(Time Passes)
Cool Tea
Tobj = Tsurr
Cup of tea at room temperature.
This arrow indicates heat transfer from the tea to the surrounding air.
Tobj >Tsurr
Hot Tea
Steam rising off the hot cup of tea.
A hot cup of tea.
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Ch 6, Lesson A, Page 2 - Heat and the First Law