Please exlpain the difference between centrifugal force and centripetal force?

Try these sites:

http://newton.dep.anl.gov/askasci/phy00/phy00305.htm

http://www-istp.gsfc.nasa.gov/stargaze/Sframes3.htm

thanks so much for the sites John they did help me alot...

Samantha..
John's sites are very good, but don't feel bad because you find it difficult to understand this concept, because EVERYONE finds it difficult to understand. When I watch my washing machine spin out, surely the clothes fly outward toward the tub wall, as if some outward centrifugal force is acting on them, when in actuality, it is a centripetal force acting inward on them as they hit the wall (the wall is pushing them in toward the center). This seems to defy common sense, because one would think that if the wall was pushing them to the center, why the heck are they clinging to the darn wall?? The answer lies in the fact (I think) that they are moving toward the center, but their high forward tangential velocity around the wall keeps them moving in a circle. And getting back to that 'centrifugal' outward flying off of the clothes toward the wall as the machine starts spinning, what's really happening here is that as the machine starts to spin, there is no contact to provide the centripetal force, so the clothes fly off tangentially to the spin until they hit the wall, then the centripetal force starts acting.

I think that the centripetal force (from gravity) acting on our orbiting astronauts is also difficult to comprehend. Good question.

Gerry, Thanks so much for the information that is a hard one for me to understand and you have made it much easier for me now

The wall of the laundry tub does not exert centripetal 'force'. The objects in the tub achieve momentum due to the spin. According to Newton, the object will continue in a straight line forever, unless some other factor affects its motion.

So the object, in this case a black sock, is set in motion by the spinning of the washer. The impetus of the motion would drive it straight out of the washer. But bump! It hits the wall of the washer, and stops. Depending on whether there is water in the tub, the sock may re-enter the water, carried by the force exerted by the flowing water. But when all the water has flowed from the tub, the clothes will stick to the wall...

UNLESS the weight of the wet clothes is sufficient to overcome the surface tension of the water in the clothes and cause them to drop to the bottom of the tub,

OR the clothes have been distributed in such a way, by the mechanics of the interplay between madly cycling water, receding in height, and the clothes being deposited at the sides of the tub by the spin, that the 'bottom' clothes form a wide enough band to support the weight of the clothes at higher levels.

IMPORTANT:

The case of the spinning planets travelling round the sun is quite different from the washing machine example, because in the case of the solar system, the sun and the planets are acting under the force of mutual gravitational attraction.

The gyrator (if any) of the washing machine has not enough mass to overcome the inertia of the spinning sock.

[This message was edited by babthrower on 01-14-03 at 12:07 AM.]

I sort of expected that there would be many different interprertations of centripetal force, let alone centrifugal "force". I don't see any real difference of centripetal force examples whether it be a spinning wash tub, a spinning carnival ride, a yo-yo with a string spinning in a horizontal circle, a planet orbiting the sun, or an astronaut orbiting a planet. In all cases, curvilinear motion is required, which neccesitates a change in the direction of the velocity with time. Any velocity (or momentum) change with time implies an acceleration. An acceleration requires a force, which is a centripetal one directed towards the center for constant tangential speed. In the washing machine or carnival ride example, the wall provides that (normal) force. Without the wall, there'd be no force, and the object would fly off in a straight line unaccelerated. In the yo-yo example, the string provides that (tension) force. In the orbiting examples, it is gravity that provides that force. Without gravity, the astronaut could not stay in orbit.

Samantha, maybe this will help. Tie a string on a weight of some sort and whirl it arouind your head. The centripetal force is the force exerted by the string, because it is forcing the weight to travel in a constantly changing direction. The weight “wants” to travel in a straight line, in keeping with Newton’s laws. What we refer to as centrifugal force is really just the reaction to the centripetal force, because for every action there is an equal and opposite reaction; again according to Sir Isaac. Leave go of the string and the weight tends to fly off in a straight line, and if it weren’t for gravity, it would.

And as a small footnote : it is illegal to possess 'gravity' knives and the like in many countries. The UK is one. Our law prohibited, among others,locking knives where the operator swung his arm like someone throwing a frisbee and the force hurled the blade out from inside the handle, to lock ready for attack . The law banned any knife operated 'by centrifugal force'. The Defence called a former Nobel Prize winning scientist to say that the force was centripetal, not centrifugal ! Sadly for the defendant, the Court, though accepting the learned man's explanation, found that it knew what Parliament had meant even if what Parliament's draftsmen ( all lawyers not scientists, of course)had written did not satisfy the scientific criteria!