Newton's Second Law

Newton’s Second Law tells you how a force changes an object’s motion: the more net force you apply, the more its speed or direction changes. It also shows that mass matters, because the same force produces less acceleration on a heavier object. This relationship works because force is the cause and acceleration is the effect, so measuring both lets you predict motion quantitatively.

Use this when you know the net force on an object and want to find its acceleration, or when you know the mass and acceleration and need the force. It is common in mechanics problems involving pushing, pulling, lifting, braking, and any situation where motion changes under a net force.

• using total force instead of net force
• mixing up mass and weight
• forgetting to keep units in kilograms, newtons, and m/s²