Centripetal force — Science definition
The net inward force required to keep an object moving in a circle; F = mv²/r. It is supplied by a real force such as tension, friction, or gravity.
Where it is taught
- Circular Motion & Gravitation — Forces, Rotation & Equilibrium, Physics & Environmental Science, Grade 12
In use
By Newton's second law, an acceleration requires a net force in the same direction, so circular motion demands a net inward force called the centripetal force, F = ma = mv²/r.
Circular Motion & Gravitation
Questions using centripetal force
Problem 1
Answer and explanation
18 N
F = mv²/r = 2 × 6² ÷ 4 = 2 × 36 ÷ 4 = 72 ÷ 4 = 18 N.
Problem 2
Answer and explanation
Even at constant speed the satellite's direction is always changing, and any change in velocity is acceleration — here it is centripetal acceleration pointing toward Earth's center. The force supplying it is gravity: Earth's gravitational pull provides exactly the mv²/r needed to bend the satellite's path into a circle, so it 'falls around' the planet.
Problem 3
Answer and explanation
6000 N
F = mv²/r = 1,200 × 20² ÷ 80 = 1,200 × 400 ÷ 80 = 1,200 × 5 = 6,000 N, directed toward the center of the curve.
Problem 4
Answer and explanation
ac=v²/r=8 m/s². Speed can be constant while velocity direction changes. Centripetal force is the net inward force, not an extra interaction added to gravity or tension.
Response criteria
- State a scientifically accurate conclusion.
- Show the calculation or mechanism that supports it.
- Include units, conditions, or limits where relevant.