VCE · Topic explainer
What are Newton’s three laws of motion?
Newton’s first law says velocity stays constant if the net force is zero. The second links net force to acceleration, ΣF = ma for constant mass. The third says interacting objects exert equal and opposite forces on each other. Those forces act on different objects.
Worked example
A 6 kg trolley is pulled right with 18 N while friction on it acts left with 6 N. The vertical forces balance. The horizontal net force is 12 N to the right, so the trolley accelerates right at 2 m/s².
For the third law, pair the rope’s pull on the trolley with the trolley’s pull back on the rope. The pull and friction in the net-force calculation act on the same trolley and come from different interactions.
Official exam practice
Find other years and marking guidance in the Physics official exam archive.