# Centrifugal Force

member 529879
How exactly does the centrifugal force work? What causes it? Why is it considered a fictous force?

FactChecker
Gold Member
To an observer in stationary, Newtonian, space, objects fly out from the center of rotation just because they want to keep going in a straight line instead of circling around. No force is necessary to explain it. F=MA can be used the way Newton intended without dreaming up any new force. But an observer who is rotating and wants to apply F=MA in his rotating space, has to invent a force to explain why objects want to fly out from the center of rotation. Centrifugal force fits that need. He invents a force so he can use Newton's F=MA in his rotating, non-Newtonian space.

• member 529879
member 529879
Okay it's starting to make more sense now, but how is it that it points opposite the centripetal force and not in the direction of motion?

Staff Emeritus
Have you ever been spun quickly, like in an amusement park ride? In which direction do you feel a force?

• member 529879
FactChecker
Gold Member
Okay it's starting to make more sense now, but how is it that it points opposite the centripetal force and not in the direction of motion?
The velocity is always tangential to the circle, so the bend in the velocity (the acceleration) is always toward the center. To make a free object take that turn, and not fly away straight, you must apply a centripetal force. That centripetal force is opposing the centrifugal force that tries to make the object fly away (actually just go straight away at the tangent velocity)

• member 529879
member 529879
Okay, I understand now that the centrifugal force opposes the centripetal force. But why exactly? If you imagine a car is rotating around a circular path in the labeled diagram below, the centripetal force is caused by static friction, and that people in the car will feel as if they are pushed to the left while turning. Can somebody explain why though that the friction is not opposing the path of inertia, and the centrifugal force is not in the same direction of the path of inertia.

#### Attachments

Khashishi
People in the car will feel pushed to the right, not the left, (assuming you are looking down on them from above).
The path of inertia is a straight line. Friction between the wheels and the ground create a force on the car to the left (as viewed by the passengers). This is centripetal force. The passengers feel propelled to the right side of the car. The latter is centrifugal force.

A.T.
Okay, I understand now that the centrifugal force opposes the centripetal force. But why exactly?
To make Newtons 2nd law work, as explained in post #3.

Centrifugal force is an inertial force that results from the change in momentum created by the centripetal force.

Think about when a car accelerates FORWARD but you feel a force pushing you BACK into your seat. That is the inertial force reacting the change in momentum of the car. Centrifugal force is the same thing, except it reacts the car's centripetal acceleration.

Look up D'Alembert's Principle for more reading on the topic of inertial forces.

A.T.
Centrifugal force is an inertial force that results from the change in momentum created by the centripetal force.
The inertial centrifugal force (in a rotating frame) acts on all objects, even those on which no real centripetal force is acting.

The inertial centrifugal force (in a rotating frame) acts on all objects, even those on which no real centripetal force is acting.
In a rotating reference frame all objects are by definition subjected to a centripetal acceleration. After all, a rotating reference frame is an accelerating reference frame (aka 'non-inertial') where the acceleration vector is centripetal.

A.T.