Centrifugal and centripetal force!?

As far as I am concerned, this problem is never better explained than right here:

http://xkcd.com/123/

Checked it out?

So now imagine a ball on a string hanging down. Now you apply a force tangential to the circle that the string *could* describe. In order for the ball to actually trace the circle, you need to continue to apply a force tangential to the circle.

This is not really enough on its own though. If you apply a force in a straight line, you get a straight line movement. So there must be another force 'pushing' the ball into a circular motion. This is the centripetal force. Its also the force the holder applies to the ball-string.

Centrifugal force is computed in a totally different way. Its a co-ordinate transform. But perhaps the easiest way to imagine it is to try wikipedia:

...The force with which the passenger pushes against the door is real. That force is called a reaction force because it results from passive interaction with the car which actively pushes against the body. As it is directed outward, it is a centrifugal force. Note that this real centrifugal force does not appear until the person touches the body of the car (ignoring any force exerted by the seat on the person's body, etc). The car also exerts an equal but opposite force on the person, called a "centripetal force".

When viewed from an inertial frame of reference, the application of Newton's laws of motion is simple. The passenger's inertia resists acceleration, keeping the passenger moving with constant speed and direction as the car begins to turn. From this point of view, the passenger does not gravitate toward the outside of the path which the car follows; instead, the car's path curves to meet the passenger.

Confused much?

Just remember that some things physicists use are meant to make their lives easier (for perfoming calculations) rather than being easier to understand. Its a bit like those alphabet things you see in primary school classrooms - the point initially is to teach the letters, but after you learn the letters you don't use the funny 'E' that looks like an elephant for writing with...

First I must comment that your formula is not valid. F = (m* V * V )/R There is no "g" in the equation itself. in F = m a, F is the RESULTANT FORCE. This is routinely used. There may be many applied forces but if an object accelerates then we know the resultant of all of them put together. Similarly in a circle. If it moves in a circle then F = m a ( as a vector) and F = m v^2 /r correctly shows the RESULTANT FORCE necessary to cause this action. No matter how many individual forces that are applied we know the effective result of them all put together. The term for this resultant force is centripetal force. It is quite real. And the term SHOULD be used because it correctly describes the situation. However the terminology is not always used precisely. In the case of the aircraft, the total of all other forces will equal centripetal force if the plane is moving in a circle with constant speed. It "balances" only in the way that the left hand side of any "equals sign" balances the right hand . side. In the case of letting the ball go, you remove the force of the string so you are no longer forcing the ball to move in a circle. Therefore the ball must move in a straight line at constant speed. This is the equivalent of stopping pushing something. It continues in a straight line at constant speed just as your ball does when you stop pulling it. ( See Newtons laws). Centrifugal force is a force that seems to be present. It seems as if an object is pulling outwards. It can be seen that this is untrue. If an object is really trying to move outwards ( A positive charge being repelled by a nucleus for example) then it accelerates directly outwards as soon as any other forces are removed. This is not the case for the ball So centrifugal force is not correct although there can be circumstances where it is a useful fiction..

consider a man rotating a ball connected to a string. The force exerted by the man's finger on the ball through the string is called centripetal force.In other words, it is the inward force or the force acting along the radius of the circle formed by rotating the string.

The centrifugal force is the force produced due to circular motion. Iconsider if a force is applied on the ball without tying it to a string. It will move in the direction of the applied force. But since we are tying a string, the ball cant move in a straight direction. How ever it tries to do this by moving in a circle. On each point on the circular path, the centrifugal force acts as a tangent to the circe.

Centrifugal Force In Driving

The centrifugal force acts on the source of the centripetal force to displace it radially from the center of the path. Thus, in twirling a mass on a string, the centripetal force transmitted by the string pulls in on the mass to keep it in its circular path, while the centrifugal force transmitted by the string pulls outward on its point of attachment at the center of the path. The centrifugal force is often mistakenly thought to cause a body to fly out of its circular path when it is released; rather, it is the removal of the centripetal force that allows the body to travel in a straight line as required by Newton's first law. If there were in fact a force acting to force the body out of its circular path, its path when released would not be the straight tangential course that is always observed...

Centrifugal force is a term which may refer to two different forces which are related to rotation. Both of them are oriented away from the axis of rotation,

but the object on which they are exerted differs. Force which is oriented toward the axis of rotation is called a centripetal force.

A centrifugal governor regulates the speed of an engine by using spinning masses that respond to centrifugal force generated by the engine. If the engine increases in speed, the masses move and trigger a cut in the throttle.

A centrifugal clutch is used in small engine powered devices such as chain saws, go-karts and model helicopters. It allows the engine to start and idle without driving the device but automatically and smoothly engages the drive as the engine speed rises.

Centrifugal forces can be used to generate artificial gravity. Proposals have been made to have gravity generated in space stations designed to rotate. The Mars Gravity Biosatellite will study the effects of Mars level gravity on mice with simulated gravity from centrifugal force.

Centrifuges are used in science and industry to separate substances by their relative masses.

Some amusement park rides make use of centrifugal forces. For instance, a Gravitron’s spin forces riders against a wall and allows riders to be elevated above the machine’s floor in defiance of Earth’s gravity.

Spin casting and centrifugal casting are production methods that uses centrifugal force to disperse liquid metal or plastic throughout the negative space of a mold.

The centripetal force is the external force required to make a body follow a circular path at constant speed (speed being the magnitude of velocity). The force is directed inward, toward the center of the circle or "oriented toward the axis of rotation"; force which is directed outward is centrifugal force.

The centripetal force always acts perpendicular to the direction of motion of the body

For a satellite in orbit around a planet, the centripetal force is supplied by the gravitational attraction between the satellite and the planet, and acts toward the center of mass of the two objects. For an object at the end of a rope rotating about a vertical axis, the centripetal force is the horizontal component of the tension of the rope, which acts towards the center of mass between the axis of rotation and the rotating object. For a spinning object, internal tensile stress is the centripetal force that holds the object together in one piece.

Centrifugal force is a virtual force. It is not really a force. There are

some situations you can be in that have you accelerating without speeding

up. One of these is a carnival ride that spins around in a circle at a

constant speed. I know one where you feel pressed against the wall very

tightly, and then the floor drops out. Most people would believe they were

moving steadily, with there bodies being pressed tightly against the wall

(outward, in a cetrifugal direction). This is centripetal force. This is

not really what happens.

When moving fast, a great deal of force is required to make you change

direction. Your body "wants" to continue in a straight line. The curved

wall gets in the way. The wall pushes in against your body. The "outward

force" is just your body trying to move in a straight line. It is not a

force at all. It is inertia, your body resisting the effects of the forces

it feels.

Virtual forces exist when your body is accelerating. Objects moving in a

steady direction at a steady speed appear to accelerate, as you see them.

Place a ball on a car seat while moving at a steady speed. Have the driver

slam on the brakes. Observe the ball appear to be pushed forward and off

the seat. The ball just continued to move forward. It is the car that felt

the backward force of the brakes. Hang a heavy ball from a spring in an

elevator. As the elevator begins to rise, the ball begins to move, as if

someone pushed down on it. It is the ball just "trying" to stay still as

the elevator accelerates upward. While rising, you can stop the motion. It

will start again when the elevator stops. The faster the acceleration (the

more you can "feel" it in your body), the stronger the virtual forces appear

to be.

Consider a body in rotational motion. The force that acts outward [away from the centre of the circle described by it] is the centrifugal force.

The force acting towards the centre of the circle is the centripetal force.

I HOPE THAT HELPS!!!

The centripetal force is the external force required to make a body follow a circular path at constant speed (speed being the magnitude of velocity). The force is directed inward, toward the center of the circle or "oriented toward the axis of rotation"; force which is directed outward is centrifugal force. Hence centripetal force is a force requirement, not a particular kind of force. Any force (gravitational, electromagnetic, etc.) can act as a centripetal force. The term centripetal force comes from the Latin words centrum ("center") and petere ("tend towards", "aim at."), and can also be derived from Isaac Newton's original definitions described in Philosophiae Naturalis Principia Mathematica.

The centripetal force always acts perpendicular to the direction of motion of the body. In the case of an object that moves along a circular arc with a changing speed, the net force on the body may be decomposed into a perpendicular component that changes the direction of motion (the centripetal force), and a parallel, or tangential component, that changes the speed.

The velocity vector is defined by the speed and also by the direction of motion. Objects experiencing no net force do not accelerate and, hence, move in a straight line with constant speed: they have a constant velocity. However, an object moving in a circle at constant speed has a changing direction of motion. The rate of change of the object's velocity vector is the centripetal acceleration.

For a satellite in orbit around a planet, the centripetal force is supplied by the gravitational attraction between the satellite and the planet, and acts toward the center of mass of the two objects. For an object at the end of a rope rotating about a vertical axis, the centripetal force is the horizontal component of the tension of the rope, which acts towards the center of mass between the axis of rotation and the rotating object. For a spinning object, internal tensile stress is the centripetal force that holds the object together in one piece.

Centrifugal force (from Latin centrum "center" and fugere "to flee") is a term which may refer to two different forces which are related to rotation. Both of them are oriented away from the axis of rotation, but the object on which they are exerted differs. Force which is oriented toward the axis of rotation is called a centripetal force.

A real or "reactive" centrifugal force occurs in reaction to a centripetal acceleration acting on a mass. This centrifugal force is equal in magnitude to the centripetal force, directed away from the center of rotation, and is exerted by the rotating object upon the object which imposes the centripetal acceleration in accordance with Newton's Third Law of Motion. Although this sense was used by Isaac Newton, it is only occasionally used in modern discussions.

A pseudo or "fictitious" centrifugal force appears when a rotating reference frame is used for analysis. The (true) frame acceleration is substituted by a (fictitious) centrifugal force that is exerted on all objects, and directed away from the axis of rotation.

Both of the above can be easily observed in action for a passenger riding in a car. If a car swerves around a corner, a passenger's body seems to move towards the outer edge of the car and then pushes against the door.

A centrifugal governor regulates the speed of an engine by using spinning masses that respond to centrifugal force generated by the engine. If the engine increases in speed, the masses move and trigger a cut in the throttle.

A centrifugal clutch is used in small engine powered devices such as chain saws, go-karts and model helicopters. It allows the engine to start and idle without driving the device but automatically and smoothly engages the drive as the engine speed rises.

Centrifugal forces can be used to generate artificial gravity. Proposals have been made to have gravity generated in space stations designed to rotate. The Mars Gravity Biosatellite will study the effects of Mars level gravity on mice with simulated gravity from centrifugal force.

Centrifuges are used in science and industry to separate substances by their relative masses.

Some amusement park rides make use of centrifugal forces. For instance, a Gravitron’s spin forces riders against a wall and allows riders to be elevated above the machine’s floor in defiance of Earth’s gravity.

Spin casting and centrifugal casting are production methods that uses centrifugal force to disperse liquid metal or plastic throughout the negative space of a mold.

[From Wikipedia, the free encyclopedia]