Suppose a mass is moving in a circular path on a frictionless table as shown in figure. In the Earth’s frame of reference, there is no centrifugal force pulling the mass away from the centre of rotation, yet there is a very real force stretching the string attaching the mass to the nail. Using concepts related to centripetal force and Newton’s third law, explain what force stretches the string, identifying its physical origin.
There is a real force acting on the string due to the mass of the mail.
When a mass is rotated, the apparent outward force on it is called centrifugal force.
The mass is moving in such a circular path where the force of friction plays no part, but a net centripetal force acts towards the center.
Also, as the nail is attached to an inextensible string, a net tension force acts on the string which pulls it outwards, and as known according to Newton’s third law of motion, every action must have an equal and opposite reaction. Therefore, this tension force and the centripetal force both are equal and act in opposite directions to each other. Thus, there is a real force acting on the string due to the mass of the mail.
A number of amusement parks have rides that make vertical loops like the one shown in Figure. For safety, the cars are attached to the rails in such a way that they cannot fall off. If the car goes over the top at just the right speed, gravity alone will supply the centripetal force. What other force acts and what is its direction if: (a) The car goes over the top at faster than this speed? (b)The car goes over the top at slower than this speed?
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