Motion and Force

A force is a push or pull that changes (or tends to change) an object's state of motion or shape. Forces are measured in Newtons (N). Newton's three laws of motion describe how forces govern movement: 1st Law (Inertia): An object at rest stays at rest; an object in motion continues at constant velocity unless acted on by a net external force. 2nd Law: Net force = mass × acceleration (F = ma). Greater force produces greater acceleration; greater mass requires more force for the same acceleration. 3rd Law: Every action has an equal and opposite reaction. Speed, velocity, and acceleration describe motion. Speed = distance/time; velocity adds direction; acceleration = change in velocity/time. Friction (opposing motion) and gravity (attraction toward Earth) are two everyday forces. Weight = mass × gravitational field strength (W = mg, g ≈ 10 N/kg on Earth). Free-body diagrams help analyse balanced and unbalanced forces on objects.