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Physics

Inertial Frame of Reference

Quick fact

Galileo famously argued that you cannot tell whether a ship is moving at constant speed or is stationary by observing the behavior of objects below decks – the first statement of the principle of relativity.

Why this is interesting

When you're sitting in a smoothly moving train, a ball on the floor stays still. But if the train brakes hard, the ball rolls forward – why does it suddenly seem to move without any apparent push?