Newton's Laws of Motion

An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted upon by a net external force.

The tendency of an object to resist changes to its state of motion. Greater mass means greater inertia.

The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass: F = ma.

F = ma = 10 kg × 3 m/s² = 30 Newtons.

For every action, there is an equal and opposite reaction. Forces always come in pairs acting on different objects.

Mass is the amount of matter in an object (measured in kg) and is constant everywhere. Weight is the gravitational force on that mass (W = mg) and varies with gravitational field strength.

The SI unit of force — defined as the force needed to accelerate a 1 kg object at 1 m/s². 1 N = 1 kg·m/s².

Acceleration doubles. From F = ma, if F doubles and m is constant, then a must double to maintain the relationship.

A rocket pushes exhaust gases downward (action); the gases push the rocket upward with equal force (reaction), propelling it into space.

An object is in equilibrium when the net force on it is zero — it is either at rest or moving at constant velocity.