Centripetal force is essential to maintain circular motion. If it is insufficient (or has been removed) then the circular motion cannot be sustained. For instance, when a car is making a turn, it is describing an arc of a circle. What provides the centripetal force is the friction between the tyres and the road.

If the road is covered by ice, the friction between the tyres and the road is greatly reduced. Consequently, the centripetal force may not be sufficient to sustain the circular motion, and the car then skids off the road by maintaining its linear velocity.

How centripetal force helps Washing machine operation | Centripetal Force and Washing machine physics

Let’s see how centripetal force helps a washing machine to operate and wash clothes. Concepts of centripetal force are behind washing machine functionality. As clothes are put inside the drum and the drum is filled with water and the power supply is switched on, circular motion sets into the drum.

The circular motion of the drum transmits similar motion to the clothes as well. But as the clothes are not physically attached to the center of the drum, they don’t get any centripetal force to continue the circular motion uniformly.

As a result, they tend to move in a straight line tangent to the circular path. But they face the drum body on their way, hit it forcefully, and revert back. Rotating drum again injects circular motion to the clothes and this cycle continues.

But this doesn’t happen to the water droplets in the clothes. As the clothes hit the drum body, as described above, the water droplets make their way to the outside of the drum, through the holes on the drum body. And the clothes get rid of the water(and dirt) by the time the washing cycle completes. This briefly describes washing machine physics.

Is there any contribution of centrifugal force in the washing machine operation?

No. As said above centrifugal force is a pseudo force. It does not have any contribution to the Washing machine. The centripetal force concept is behind washing machine operation.

Is centrifugal force a reaction of centripetal force?

No. Centrifugal Force is not a reaction force of the centripetal force. Centrifugal Force is a pseudo force that doesn’t even exist in reality. So it can’t be a reaction force. The reaction force for centripetal force is actually known as Centrifugal Reaction.

How Is Centrifugal Reaction the reaction force of centripetal force? Explain with Newton’s 3rd Law

As per Newton’s 3rd Law, Centripetal Force must be having an equal and opposite reaction force.

Yes, it has. It’s called Centrifugal Reaction. Please note that it’s not the same as Centrifugal Force. The concept of centrifugal force is completely different and it’s not even a real force.

Coming back to Centrifugal Reaction! When we rotate a piece of stone with our finger through a tied string, then the finger also feels a force that is applied by the rotating stone. This is a Centrifugal Reaction force.

Centrifugal Reaction (CR)

Now as its direction is opposite to the Centripetal force (finger feels a force which tries to drag it outwards, away from its central position), it’s Centrifugal, and as it’s a reaction force, so we call it as Centrifugal Reaction force.

Pls, note that: Centrifugal reaction is not centrifugal force.

Difference between centripetal force and centrifugal force

Centrifugal Force is a pseudo force, it’s not a real force. But, Centripetal force is a real Force because it evolves due to the mutual interaction of objects or masses. Centrifugal force is felt only within a Rotating Frame of Reference but doesn’t exist in reality.

If a person shares the same frame of reference as a rotating object, then that object will apparently look like a static object to that person.
The person within a rotating frame of reference will never understand the reason for Centripetal Force being applied because for him that frame of reference is static and for something static there is no need for any force to be applied.

Rather he will feel as if some external force is being applied which is pulling the entire system away from the central position and there is another force directed towards the center which is balancing the first one.



What is the Centripetal Force formula?


The formula of Centripetal force is F= mass x Centripetal Acceleration = mv2/R = mω2R, where m is the mass of the object moving in a circular path, ω is the angular velocity of that object, and R is the radius of the circular path.


The features of circular motion evident from the Centripetal force formula is listed below:

1) An object with more mass would be requiring less angular velocity and a smaller radius of circular motion, to maintain its circular motion.

2) If R is high, even a lower angular speed can keep an object rotating in a circular path.

3) If R is too small, then angular velocity has to be at the higher side to compensate for the small R and generate the necessary Centripetal Force required to continue the circular motion.

Why is the centrifugal force called a pseudo force?

Centrifugal force is called a pseudo force or non-existing force. Let’s find out why. When passengers travel in a bus and the bus takes a sharp turn, then the passengers feel thrust in the opposite direction. Here the bus is an example of a Rotating Frame of Reference and the passengers within that frame of reference feel a pseudo force, an unreal force! (see the diagram below) This pseudo force is called Centrifugal Force.

The road beside the bus is a static frame of reference.

A person standing in that static frame will never reciprocate the presence of centrifugal force for that bus, to him the movement of the passengers is just because of directional inertia.

how is this centripetal force being applied to the stone being rotated by a string?

When a stone is rotated by a string tied with a finger then the centripetal force is transferred from the finger to the stone and this transfer is happening via the string only.

Who is supplying this centripetal force here? The finger.

That’s why when the string is released or the string is torn this force can’t pass to the stone anymore. This is the instance when Newton’s First Law of motion comes into play. As there is no force (net force) on the stone so it will continue along its last direction on the circular path. And the direction is actually the tangent to that point on the circular path.

Centripetal Force is a real force – Who or What is supplying this?

Any force can be a centripetal force. Centripetal force is the umbrella term given to any force that is acting perpendicular to the motion of an object and thus causing it to go in a circle.

1) In the above example, a stone is rotated in a horizontal plane with a string tied with a finger. Here the finger supplies the required centripetal force that makes the stone rotate. There are a few other instances when the supplier of this force varies from case to case.

2) Electron orbits the nucleus in an atom. The electrical attraction force generated between an electron and the nucleus supplies the centripetal force on the electron.

3) A car or a bike taking a circular bend – The Frictional force between the tires and the road supplies the required Centripetal force. (As it is a frictional force so certainly it has a maximum limit, beyond which balancing in a bike at a circular bend won’t be possible. It’s a different story, will take this in a separate post)

4) The satellite revolves around the earth. Here Gravitational Attraction between the earth and the satellite supplies this centripetal force.

List of Common circular motions and the suppliers of centripetal force (in tabular format)
Any force can be a centripetal force. Centripetal force is the umbrella term given to any force that is acting perpendicular to the motion of an object and thus causing it to go in a circle.MotionProvider of centripetal forceWhirling rock on a stringThe stringElectron orbiting atomic nucleusElectron nucleus electrical attractionCar corneringFriction between tyres and roadMoon revolving around EarthMoon–Earth gravitational attractionSatellite revolving around EarthSatellite Earth gravitational attractionList of Common circular motions and the suppliers of centripetal force (in a table) of Common circular motions and the suppliers of centripetal force (in a table) of Common circular motions and the suppliers of centripetal force (in a table)

Is centripetal force real?

Note that this centripetal force is a real force. In all the above examples, you can see that this force is supplied by real forces like gravitational force, electric force, or frictional force.

Centrifugal force, on the other hand, is a pseudo force.

When can Gravity Act as a Centripetal Force?

The force of Gravity causes an attraction between two objects of mass m1 and m2 at a distance of r and this force is expressed as Fg = Gm1m2/r2

By Newton’s Third Law, both objects experience the force: equal in magnitude and opposite in direction, and both will move as an effect of it.

If one of the objects is much lighter than the other (like the earth is to the sun, or a satellite is to earth) we can approximate the situation by saying that the heavier mass (the sun) does not move, since its acceleration will be far smaller due to its large mass. (acceleration= force/mass)

Then, if the lighter mass remains at a relatively constant absolute distance from the heavier one (remember, the centripetal force needs to be constant in magnitude), we can say that the lighter mass experiences an effectively centripetal force.

Gravity is not always a centripetal force. This is a really important point. It only acts as a centripetal force when conditions approximate those listed above.

Equation of Centripetal gravity

If gravity provides centripetal force and acceleration, we can write the following equation.
Fg = Gm1m2/r2 = m1 v2 /r …………… (i)
It’s important to remember that m1 refers to the lighter mass since that is the one traveling. Then simplifying (i),
Gm2=v2. r ………………………….......  (ii)
r is the radius of the orbit and v is the orbital velocity.