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Lesson · Grade 10 · Science

Open and Closed Systems: Following Energy Across the Boundary

  • Grade 10
  • Science
  • 1 min 56 s
  • British Columbia
  • BC10-SC-39

A pot of water on a stove gets a dashed boundary that separates the system from its surroundings. With no lid, energy and steam both cross it (an open system); with a sealed lid only energy crosses (a closed system), and a worked example shows energy in = change in stored energy + energy out (5000 J = 4000 J + 1000 J). The video corrects the mistaken idea that a closed system can't gain or lose energy (a system where nothing crosses is isolated), then shows Earth as nearly closed: very little matter crosses, but sunlight comes in and infrared goes back out to space.

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In one sentence

The question this lesson answers

When you heat a pot of water, where does the energy go?

A system is the part of the world we choose to study. Here, it is the pot and the water.

Transcript

What the lesson says

When you heat a pot of water, where does the energy go?

A system is the part of the world we choose to study. Here, it is the pot and the water.

A dashed line called the boundary marks its edge. Everything outside is the surroundings.

The hot stove transfers energy into the system by heating.

With no lid, this is an open system: energy and matter can both cross.

Energy leaves by heating the air, and steam carries water out of the pot.

Seal it with a lid, and it becomes a closed system: energy can cross, but matter cannot.

Energy that stays inside is stored, so the water gets hotter.

For any system, energy in equals the change in stored energy plus energy out.

Say that in 10 seconds, 5000 joules go in and 1000 joules escape to the air.

So the stored energy rises by 5000 minus 1000, which is 4000 joules.

A common mistake is to think a closed system cannot gain or lose energy.

But our sealed pot just gained 4000 joules. Closed means matter cannot cross, but energy can.

A system that cannot gain or lose energy is isolated: neither energy nor matter can cross.

Earth is nearly a closed system: very little matter enters or leaves it.

But energy crosses all the time: sunlight comes in, and invisible infrared radiation goes back out to space.

Open systems let energy and matter cross; closed systems let only energy cross.

Curriculum

Where this fits

British Columbia, Grade 10

Science 10, Physics: transformation of energyBC10-SC-39

Previous: Kinetic energy: why doubling speed gives four times the energyNext: Specific heat capacity: Q = mcΔT

The outcomes and strands follow the British Columbia curriculum.

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