Part 04 · Rotation and gravity · Card 3 of 11
Centripetal force
The net inward force needed for circular motion, F = m v squared / r. It is a role played by tension, friction or gravity.
Last updated
Analogy
Not a new force, just a job given to an existing one.
Example
Friction on bend
F = m aF = 1000 x 4.5F = 4500 N
In practice
A 1000 kg car on that bend needs 4500 N of sideways friction.
Practice
Flashcards
- What gives a satellite its centripetal force?Gravity from the planet.
Interview questions
- Derive the speed of a satellite in circular orbit and use it to find the period of a satellite at radius r.
- Gravity equals m v^2 / r
- v = sqrt(GM/r)
- Period = 2 pi r / v
Questions people ask
Is centripetal force a new type of force?
No. It is the name for the net inward force, whatever supplies it. For a car on a flat bend it is friction. For a ball on a string it is tension. For a satellite it is gravity. Never add it as an extra force on a diagram.
What happens if the centripetal force suddenly disappears?
The object flies off in a straight line along the tangent to the circle, not outward along the radius. If you let go of a swinging ball on a string, it moves along the direction it was travelling at that moment, as Newton's first law says.