Newton's Second Law

When a net force pushes on an object, the object accelerates — it speeds up, slows down, or changes direction. The bigger the force, the bigger the acceleration; the more massive the object, the smaller the acceleration.

F = m · a

• F — force (N): the net push or pull acting on the object
• m — mass (kg): how much matter the object has — its resistance to being accelerated
• a — acceleration (m/s²): how quickly the object's velocity changes each second

A 2 kg cart on a frictionless floor is pushed with a steady 8 N force. How quickly does it speed up?

• m = 2 kg
• F = 8 N

1. a = F / m
2. a = 8 N / 2 kg

a = 4 m/s²

The same 8 N push now acts on a heavier 4 kg cart. What is its acceleration?

• 4 m/s²
• 2 m/s²
• 32 m/s²

To give the original 2 kg cart twice the acceleration (8 m/s²), the force must be…

• 16 N
• 4 N
• 8 N