Although centrifugal force is omnipresent in our daily lives, is it really what we believe it to be?
It is when we turn in a car, or an airplane. It is also evident in spin cycles of washing machines and children riding on merry-go round. It may one day provide artificial gravity to spaceships and stations.
Because they are so closely related, centrifugal force and centripetal force are often misunderstood.
According to Merriam Webster Dictionary, centripetal force can be defined as: "The force necessary to keep an object moving along a curved route and that is directed inwardly toward the center or rotation." While centrifugal force can be defined as "the apparent force felt by an object that moves in a curving path that acts outwardly from the center or rotation."
While centripetal force can be described as an actual force, it is also known as a centrifugal force. This means that when you twirl a mass on a string, it exerts an inward centrifugal force upon the mass. However, the string appears to exert an inward centripetal effect on the mass.
Andrew A. Ganse is a University of Washington research physicist. He said that the difference in centripetal force and centrifugal forces has to do with different "frames of reference", which are different perspectives from which one measures something. "Centripetal and centrifugal forces are the exact same force. However, they are experienced from different frames.
You can see a rotating body from the outside. This forces it to follow a circular path. If you are part the rotating system, however, you feel an inward centripetal force pulling you away from the center. However, what you really feel is the inward centrifugal force keeping you from going off on a tangent.
Centripetal pulls the rotating object inward, while centrifugal is the force that pushes it outward. (Image credit to Future)
1. Centripetal force
This force pulls an object towards a circle's centre.
2. Velocity
If an object's velocity is perpendicular with the direction in which a force is applied (e.g. tension on a rope), it will move in circles.
3. Acceleration
If an object moves closer to the centre, the centripetal force will increase.
4. Centrifugal force
This is the force that is generated when an object rotates.
5. Tangential direction
If the force that keeps an object in motion is broken (e.g. cutting the string holding a spinning ball), the object will fly in a straight line following the tangential direction.
6. Inertia
Newton's first law states that an object will always move in a straight line, unless it is acted on by another force such as friction on a road, tension, gravity, or friction on a spring.
Newton's Laws of Motion and Centrifugal Motion
Newton's Laws of Motion describe this apparent outward force. Newton's First Law says that a body at rest will stay at rest and a body moving will move unless an external force acts upon it.
A massive body moving in space in a straight line will be inertia. Unless an external force causes it speed up, slow down, or change direction, it will continue moving in the same straight line. A continuous centripetal force (F) must be applied at an angle to the body's path in order to allow it to follow a circular route without speed changes. The radius (r), of this circle, is equal to the mass of the vehicle (m) multiplied by the centripetal force(F) or r = Mv2/F. You can calculate the force by simply changing the equation F= mv2/r.
Newton's Third Law says that for every action there is an equal or opposite reaction. The ground seems to exert an opposite force to your feet, just as gravity causes you exert a force against the ground. In an accelerating car, you feel the seat exert a forward force on your feet just like you feel the seat exert a backward force.
The centripetal force pulls a mass inward so it follows a curving path. However, the mass seems to push outwards due to its inertia. However, in each case, only one force is being applied. The other is an apparent force.
Laboratory centrifuges spin quickly and exert centripetal force upon liquids like blood. These liquids are then separated based their density. (Image credit: Shutterstock)
In action: Centripetal force
Centripetal force can be used in many ways. One application is to simulate the acceleration during a space launch in order to train astronauts. It is almost impossible to move when a rocket is launched for the first time. As it ascends, however, it continues to lose mass as it burns fuel at an incredible rate. Newton's Second Law says that force equals acceleration times mass, or F = ma.
In most situations, mass remains constant. However, a rocket's mass can change dramatically while its thrust, which is the force generated by the rocket motors remains almost constant. The acceleration at the end of boost phase can increase several times the normal gravity. NASA prepares astronauts for extreme acceleration by using large centrifuges. The seat back pushing inwards on the astronaut provides the centripetal force.
The laboratory centrifuge is another example of how centripetal force can be applied. It is used to accelerate precipitation of suspended particles in liquid. This technology can be used to prepare blood samples for analysis. Rice University's Experimental Biosciences website states that "the unique structure of blood makes it easy to separate red blood cells and plasma from the other formed elements through differential centrifugation."
Thermal motion, which is the opposite of gravity, causes continuous mixing that prevents blood cells settling out of whole blood samples. A centrifuge can reach accelerations of 600 to 2,000 times normal gravity. This causes the red blood cells that are heavy to settle at the bottom of the solution and stratifies the components into layers according to density.
Additional resources:
This article was last updated by Ben Biggs, Live Science editor.
