An apple is whirled round in a horizontal circle on the end of a string which is tied to the stalk. It is whirled faster and faster and at a certain speed the apple is torn from the stalk. Why?
Answers
As the cantrifugal force is a force, arising from the body's inertia, which appears to act on a body moving in a circular path and is directed away from the centre around which the body is moving.
In a horizontal circle, a constant centripetal force of tension must be applied to maintain constant speed, since Earth's gravity does not act in the horizontal direction.
But in a vertical circle, a variable force is needed. Gravity always pulls the stone down. At the top of the circular path, gravity therefore acts toward the center of the circle. This means there is a minimum speed for this stone that would require no force of tension in the string at the top, as gravity would provide the full centripetal force. At the bottom of the circle, however, gravity is still acting downward, but here it is away from the center of the circle. The force of tension in the string must therefore counter the weight of the stone and also provide the centripetal force required to maintain the necessary speed. The slowest speed possible to maintain constant speed with a vertical circle would require that only gravity acts at the top; and thus the centripetal force must equal the weight of the rock. This must still be true at the bottom, but since gravity exerts a downward force equal to the weight of the rock, the force of tension in the string must be twice that in order to maintain a centripetal force equivalent to the weight of the rock (2mg - mg = mg).
Of course you could revolve it at faster speeds than this too, but the same basic principles apply. The force of tension in the string will always need to be greater at the bottom than at the top to maintain a constant speed.
On a related note that is probably not necessary for your circumstances, it should be noted that a horizontal circle does not mean the string is horizontal unless you are neglecting gravity. However, the angled string simply means that the vertical component of the tension will counter the weight of the stone and the horizontal component will provide the centripetal force.
thanks!! HOPE YOU UNDERSTAND
