Newton’s Laws: The New Physics Planetary Motions Newton’s Laws: The New Physics

Newton’s Laws LAW 1: A body is in natural motion when it is at rest or when moving along at a constant speed along a straight line Definition of natural motion

Newton’s Laws LAW 2: A net force applied to a mass results in an acceleration OR Acceleration is directly proportional to the net force and inversely proportional to the mass

Newton’s Laws Speed is the rate of motion (km/s) Velocity is speed with direction Acceleration is a change in velocity (speed, direction, or both!) Accelerations result from net forces (add them all!)

Newton’s Laws Circular motion is accelerated motion (even if speed constant) Why? Direction of motion is constantly changing! Planetary motions are accelerated; implies a force

Newton’s Laws LAW 3: Every force involves another equal but opposite force OR Forces act in simultaneous pairs

Falling Bodies Observation: All masses near surface of earth fall with same acceleration Inference: Gravity acts so that the greater mass is pulled by a greater force

Gravitation Interaction at a distance between masses (any size, shape) More mass => more force (directly proportional to mass) Greater distance => less force (inversely proportional to square of distance: inverse square law)

Newton’s Law of Gravitation Force is proportional to (M1 x M2)/Distance2 Outside of a body, acts as if all mass is concentrated at center Weight is a force! Predicts escape speed of one object leaving another (space travel!)

Newton’s Law of Gravitation Results in Kepler’s laws (new version of 3rd; masses!) Predicts/explains motions of planets with great precision Physical basis of heliocentric model (earth’s rotation, revolution) Powerful theory of gravitation

Newton’s Law of Gravitation Predicts interactions of masses even outside solar system: a universal physical law! Erased separation of earth and sky Newton thought cosmos infinite; otherwise all masses would have already collapsed together