Gravity, friction, swings, and heat

Ignored air, a heavy object and a light object fall together. Speed increases as the object falls. A sideways throw does not change the fall: a nut thrown horizontally and a nut dropped at the same instant hit together.

If you let go of a spinning weight on a string, it flies straight along the tangent, the direction it was already going. The string had been pulling inward. The outward yank people feel is called centrifugal force, but the free path is straight.

Friction opposes sliding. More weight or a rougher surface means more friction. Oil, rollers, or a smoother face means less. Work is force times distance moved. If the part does not move, the work done on it is zero, even if you are tired. Balanced forces mean no change in motion.

A longer ramp to the same height takes less effort and more distance. A short pendulum swings sooner than a long one. The weight of the bob does not set the time. Heat flows from hot to cold. A solid chunk of steel sinks. A hollow hull can float because of the air inside. If a scale reads lighter underwater, the difference is the buoyant force.