Newton's Second Law links force, mass and acceleration. The resultant force on an object equals its mass multiplied by its acceleration:
F = m × a
Force F is in newtons (N), mass m is in kilograms (kg) and acceleration a is in metres per second squared (m/s2). The force must be the resultant force. Rearranging gives a = F ÷ m and m = F ÷ a.
Example: a 1200 kg car accelerates at 2 m/s2. The resultant force is 1200 × 2 = 2400 N. Example: a resultant force of 1500 N acts on a 600 kg trolley, so a = 1500 ÷ 600 = 2.5 m/s2.
In an experiment with a trolley and light gates, a bigger resultant force gives a bigger acceleration for the same mass. A bigger mass gives a smaller acceleration for the same force. If the mass is doubled and the force stays the same, the acceleration is half as big.