Acceleration and Newton's laws

The idea

Acceleration a = Δv ÷ t, in m/s². For uniform acceleration, v² − u² = 2as. Newton's first law: if the resultant force is zero, an object stays at rest or moves at constant velocity. Newton's second law: F = ma. Newton's third law: when two objects interact, they exert equal and opposite forces on each other. Near the Earth's surface a falling object accelerates at about 9.8 m/s² until air resistance builds up; at terminal velocity the resultant force is zero.

1. Find the change in velocity.
2. Use a = Δv ÷ t or F = ma.
3. Check the resultant force for Newton's first law.

Watch out Newton's third law pairs act on different objects, so they do not cancel.