Birta's hot coffee sits on her desk, cooling. Energy is leaving the coffee.
To keep count of energy on the move, physics first chooses exactly what to watch. This lesson makes that choice, and names both sides of it.
Earlier in the course, you chose a set of objects and analyzed them together, and that chosen set was called the system.
Birta studies the coffee, so here the coffee is the system.
Everything outside the system still matters. The energy leaving the coffee goes into the desk under the mug and the air in the room.
Everything outside the system is called the surroundings.
For the cooling coffee: the system is the coffee, and the surroundings are the desk, the room air, and everything else outside the coffee.
The system is a choice, not a fact of nature. Study the room air instead, and the air becomes the system, with the coffee in its surroundings.
A glass of iced tea warms up on a porch table. Delia studies the tea's energy. Name the system and the surroundings.
Delia chose the tea to study, so the tea is the system.
Everything outside the tea is the surroundings.
System: the tea. Surroundings: everything outside it, including the glass, the table, and the porch air.
Emrys studies how the water in a backyard pool warms through a summer afternoon. Name the system.
Emrys chose the pool water to study.
The pool water is the system; the deck and the outdoor air are in the surroundings.
Ivo heats soup, then tracks the soup's energy as it cools in a bowl on the kitchen table. Which part of this setup is the system?
Emrys studies a tray of warm rolls cooling on a counter. The rolls are the system. What are the surroundings?
Ivo says: 'Once a system is chosen, everything outside it counts as the surroundings.' Is Ivo correct?
A sealed bag of ice sits inside a lunchbox. Delia studies the ice's energy. Which statement is correct?
Two students watch one heater warming the water in a fish tank. Birta studies the water's energy. Emrys studies the heater's energy. Which statement is correct?
Ivo studies the stew in a pot as his system. Which of these is in the surroundings?