IIT JEE , AIEEE Forum - Physics , Mechanics

sandeepjamkar

Sir in HCV there is this question for short answer about cloth dryers.Pg112.Q.2.

Some washing machines have dryers of spinning type.It consists of a drum which rotates very fast in which wet clothes ment for drying are kept.The general description is that' the centrifugal force from the drum throws water particles away'.Comment upon this statement frm point of view of GROUND & OBSERVER ROTATING ON THE DRUM.

Here i can understand frm pt of view of observer in non inertial frme as why is water being thrown out but i m confused in case of Ground observer.Plz provide a detailed explanation.

cvramana

Case of the observer on the Ground:

In this case the observer sees that there is no Centripetal Force acting on the water particles. As you know for a body to move in circular path a Centripital Force is neccessary otherwise the body cannot stay on the circle. Because to change the direction of velocity a Force perpendicular to the velocity is required. Therefore the water particles fly away from the center.

Case of the observer rotating on the drum:

For this observer there is a Pseudo Force acting on the particles, as he is in a non-inertial reference frame. Therefore the particles fly away.

vaibhav1729

ramana garu
can i expecta vivid answer

cvramana

When the trajectory of an object travels on a closed path about a point either circular or elliptical, it does so because there is a force pulling the object in the direction of that point. That force is defined as the CENTRIPETAL force. It has not been more simply, or directl6y stated than by one Isaac Newton in his famous "Principia"(definition 5):

"A centripetal force is that by which bodies are drawn or impelled, or any way tend, towards a point as to a center"

This force can be demonstrated by twirling a ball on a string, and either actually or conceptually cutting the string. The ball's trajectory is then a straight line tangential to the closed trajectory at the instant the string is cut.

This is also illustrated by what happens to the ball in the "hammer throw" of track and field. The athlete spins the heavy ball around several times then lets it fly. It takes off in a straight line.

That is really all that is necessary. The term CENTRIFUCAL force appears to have come about because of a mistaken perception that there is a force that operates in the opposite direction as the CENTRIPETAL force. But that is a misconception. The "pull" that is felt by the ball on a string or by the hammer thrower is the force that has to be applied toward the center, to keep the ball from flying off tangentially, not radially.

Unfortunately, the terms are often used interchangeably, or incorrectly. Newton's term, which I think should take the prize is CENTRIPETAL.

Similar to the hammer throw the water particles which are inside the cloth are kept spinning until the critical value of angular velocity, which makes the water particles to detach from the cloth and move tangentially, which appear to go radially outward for a person on the drum.

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