Whirl a ball on a string and let go — it flies off straight, not outward. To keep anything moving in a circle, something must pull it constantly toward the centre. That inward pull is the centripetal force.
The sun's gravity is the centripetal force here — always pointing inward. Get the speed right for the distance and it bends the path into a clean loop; too fast and the same pull only stretches it into an ellipse.
Centripetal force is the net inward force that keeps an object moving along a curved path. It always points toward the centre of the circle, and its size is F = mv²/r — bigger for a faster speed or a tighter radius. It is not a new kind of force; it is the role played by whatever real force — gravity, tension, friction — happens to point inward.
By inertia, a moving object wants to travel in a straight line. To bend that path into a circle, a force must keep pulling it off the straight line, toward the centre. This inward force produces a centripetal acceleration a = v²/r, also pointing inward. Take the force away and the object instantly flies off along the tangent — a straight line, not outward.
In The Field the sun's gravity is the centripetal force. It tugs the disc inward every frame, bending its straight inertial path into a curve. Match the speed to the distance and the inward pull is exactly what a circle needs, so the disc loops in a steady orbit. Too slow and it spirals in; too fast and the orbit stretches into an ellipse.
Centripetal force is easiest to feel when you can speed the spin up and watch the required pull grow — then cut the string and see the object fly off straight, not outward.
The required pull is F = mv²/r — doubling the speed quadruples it. Cut the string and inertia carries the ball off in a straight line, the tangent, never straight out.
Friction between the tyres and the road provides the centripetal force that curves the car around a corner. Take the bend too fast and the friction can't supply enough inward pull, so the car skids straight on.
The drum wall pushes the clothes inward, keeping them circling. The water isn't pulled in, so with nothing to bend its path it flies off straight through the holes — which is exactly how the spin gets clothes dry.
Earth's gravity is the centripetal force holding the Moon in its near-circular orbit, constantly bending its straight-line motion into a loop. Without that inward pull, the Moon would simply drift off into space.
Centripetal force is the quiet inward pull behind every turn, orbit, and spin. This FAQ runs from whirling balls and cornering cars to satellites, spin dryers, and the reason "centrifugal force" is a comfortable fiction.
Centripetal force is the inward pull that keeps an object moving in a circle. The word means "centre-seeking": it always points toward the middle of the curve. Whirl a ball on a string and the string's pull is centripetal; remove it and the ball stops circling and flies off straight. Anything moving in a circle must have some inward force doing this job.
Centripetal force is F = mv²/r, where m is the object's mass, v is its speed, and r is the radius of the circle. The speed is squared, so going twice as fast needs four times the force. A smaller radius (tighter circle) also needs more force. The force points toward the centre, and the matching acceleration is a = v²/r.
Because of inertia, a moving object keeps its velocity unless a force changes it. The centripetal force is the only thing bending the path into a circle. The instant that force disappears, nothing is left to curve the motion, so the object continues in the straight line it was travelling at that moment — the tangent to the circle, not a path straight outward.
| Property | Centripetal | Centrifugal |
|---|---|---|
| Direction | Inward, to the centre | Outward (apparent) |
| Real force? | Yes | No — a felt effect |
| Cause | Gravity, tension, friction | Inertia in a turning frame |
| Acts on | The circling object | Nothing real |
No — centripetal force is not a separate force of nature. It is a job description: whatever real force happens to point toward the centre is "acting centripetally". For a planet it is gravity, for a whirled ball it is the string's tension, for a turning car it is friction. The same familiar forces simply take on the centripetal role when they curve a path.
Friction between the tyres and the road supplies it. As the car turns, the road pushes sideways on the tyres toward the centre of the bend, bending the car's path. If the road is icy or the speed too high, friction can't provide enough inward force, and the car slides straight on, unable to make the turn. Banking the road can help by adding to the inward push.
Because centripetal force grows with v²/r. Doubling your speed quadruples the inward force needed; halving the radius doubles it. A fast, tight turn therefore demands a large inward force, which your body feels as a strong sideways press against the seat or door. That pressing sensation is your own inertia resisting the change of direction the force is imposing.
Gravity pulls the Moon (or a satellite) straight toward Earth's centre, exactly the direction a centripetal force must point. The Moon's sideways speed would carry it off in a straight line, but gravity continually bends that line into a near-circle. The orbit is a perfect balance: the inward gravitational pull provides just the centripetal force needed for the Moon's speed and distance.
The drum wall pushes the clothes inward, giving them the centripetal force to keep circling. The water, sitting in the fabric, has no such inward force once it reaches the holes — so, by inertia, it travels straight on and escapes through the openings. The spin does not throw the water out; it simply lets the water continue straight while the clothes are held in.
Acceleration means any change in velocity, and velocity includes direction as well as speed. In circular motion the speed can be perfectly steady while the direction changes every instant — and changing direction is itself an acceleration. That acceleration, a = v²/r, points toward the centre, which is why a centre-seeking force is required even for a steady circle.
Banking tilts the surface so it pushes vehicles partly toward the centre of the bend. This lets the road's normal force share the job of supplying centripetal force, instead of relying on friction alone. As a result, vehicles can take the curve faster and more safely, and the design is gentler on tyres. Steeply banked velodrome and motorway curves use exactly this trick.
No. Work is done only when a force has a component along the motion. Centripetal force points toward the centre, exactly perpendicular to the object's velocity, so it never speeds the object up or slows it down — it only turns it. That is why an object can circle at constant speed indefinitely under a centripetal force without gaining or losing energy.
If the inward force is too small for the speed and radius, the path can't curve tightly enough, so the object spirals outward or flies off. If it is larger than needed, the path curves more sharply, tightening into a smaller circle or pulling the object inward. A stable circle exists only when the available inward force exactly matches the mv²/r that the motion requires.
It is Newton's laws applied to a curved path. Newton's first law says the object would go straight without a force; Newton's second, F = ma, gives the size of the inward force as F = mv²/r, since the centripetal acceleration is v²/r. So centripetal force is not a new rule but the familiar laws of motion describing what it takes to keep turning.
Everywhere things turn. It steers cars around bends and trains around curves, holds satellites and the Moon in orbit, spins water from laundry and separates samples in a centrifuge, and presses you into your seat on a fairground ride. Engineers size it carefully — banking roads, strengthening rotor blades, planning orbits — because getting the inward force right is what keeps circular motion safe and stable.
Seven question formats, the way Beyond Dictionary serves them. Every question has layered hints — a quick nudge, the reasoning, then a deeper connection — so a wrong answer opens a door, never a dead end. 32 questions across all seven formats — multiple choice, multiple-correct, fill-in-the-blank, match, sequence, read-think-connect, and write-your-own.