Virial theorem

Ever wondered why planets don't just fly off into space?

Imagine you're throwing a ball against a wall; it bounces back. What keeps it moving back instead of flying away?

Think of the ball's motion as a dance between its energy to move forward (kinetic) and the wall's pull back (potential). The dance keeps going because the ball's forward energy matches the wall's pull back energy, on average.

Example

If you throw a ball with 10 J of kinetic energy against a wall, the wall's potential energy is also 10 J on average.

Remember this

The virial theorem shows that, over time, a stable system's average kinetic energy equals half the negative of its average potential energy.

Text adapted from Wikipedia, licensed under CC BY-SA 4.0.

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