OpenStax College Physics for AP® Courses, Chapter 7, Problem 38 (Test Prep for AP® Courses)

This is College Physics Answers with Shaun Dychko. There isn't really and truly a closed system in the real universe but we can try to get close and think about the Moon orbiting Earth is close to a closed system but even then it's not quite true since you know we have the Sun over here radiating energy towards the Earth and so the Earth is absorbing that energy and then we have this Moon zipping around the Earth and the Earth is radiating heat energy back out to the universe as well and also receiving energy from the universe too and you know that's why we see stars because light energy is hitting Earth from stars and so on... other stars besides the Sun and... yeah! And then there's also, you know, radioactive decay of material inside the Earth, which is partly responsible for the heat in the Earth that creates lava and that heat is being radiated out as well. So there's no such thing as a really closed system but anyhow, this might be a close approximation.