Newton’s Laws

Motion Velocity describes motion. –Speed and direction –At rest : no velocity Planets have a velocity at each point in their orbits. –Circle or ellipse Acceleration is the change in velocity. –Change in speed –Change in direction Orbits require acceleration. –Changing direction : circle –Changing speed: ellipse

Elliptical Motion y x Velocity points along the motion. –Red arrows Acceleration points in the direction of change. –Blue arrows

Force Force is A push or pull on an object. A property with magnitude and direction. Some forces  Fundamental forces –Electricity and magnetism –Nuclear forces –Gravity  Contact forces –Friction –Tension –Normal forces

Dynamics Ancient scientists looked to the natural properties of objects to describe motion. Newton defined motion based on forces acting from outside an object. –Motion from external forces –Three laws for motion

First Law: Law of Inertia 1 An object continues at rest, or in uniform motion in a straight line, unless a force is imposed on it. This describes constant velocity, including zero. No change means no net force, and vice versa. rocket no force constant velocity

Mass Matter has substance. –Solids, liquids or gases –Subatomic particles –Planets and stars Mass measures the amount of matter. –Standard kilogram –1 kg = 1000 g –1 hydrogen atom 1.66 x kg

Second Law: Law of Acceleration 2 The change in motion is proportional to the net force and the change is made in the same direction as the net force. Net force gives rise to acceleration. Force = mass x acceleration. –1 newton (N) = 1 kg m/s 2 Rocket: has mass Force: becomes acceleration Initial velocity Final velocity: changed by the force

Third Law: Law of Reaction 3 For every action there is an equal and opposite reaction. Forces between two objects act in pairs. F 12 =  F 21 rocket reaction force acts on the rocket rocket and gas are both affected hot gas is forced out