Moon orbiting the Earth, the planets and a car taking a bend are all instances of circular motion.Fig. 1. A fast bowler in action.The picture illustrates a bowler in action. His hand takes almost a semicircle before delivery. The moment he releases the ball it moves at a tangent to the circle.Next picture shows a thrower in action. He rotates the ball a few times in a horizontal plane and releases it. The ball flies making a 90° angle to the radius.As long as the object is in uniform circular motion there will be an un balanced force acting on it towards the centre. This is the centripetal force. This can be calculated by the formula given below. Fig. 2 Rotating a heavy mass.

The groove in the record had to pass the needle at a specific speed for accurate rendition of music. The earliest records had a rotatory speed of 78 RPM. Does this mean that the needle meets the record at a constant speed? No! not at all. As the needle approaches the centre the speed at which groove passes the needle changes. Let us do a calculation and examine how it happens. Fig.1. The record does 78 revolutions per minute. Let us assume that the needle is at the outermost point. From this we can calculate the circumference using 2πr The circumference of the record : 2x 3.14x 0.15 = 0.94 m. = 0.94 / 0.77 = 1.22 ms^{1}
Fig. 2. Rotating a fire ball at a uniform speed.
What would be the speed of the ball?

Question. 1.0
The man is turning a mass tied to a string as shown. Length of the string is 1.0 m. The object does 16 swirls in 5 seconds.
Find the following:
1.1 What is the period ‘T’ of circling?
1.2 If the thread snaps at the point D what will be the velocity of object leaving the circle ?
1.3 What is the acceleration?
1.4 If the mass of object is 400g (0.4kg) what was the tension on the string?
Question 2.0
A red disc of mass 200g is placed at the circumference of aa rotating table. The limiting friction between the disc and the table is 3 N.
2.1 What is the minimum speed necessary for it to get thrown out.
2.2 What is the number of revolutions per minute (rpm) at the time?
Question 3.0
A car having a mass of 800 kg is on a bend banked at 20˚. The radius of the curve is 50 m.
Find the following:
3.1 Vertical force on the car.
3.2 Force acting normal to the road. (N)
3.3 Horizontal component due to weight.
3.4 Maximum speed it can use without any friction on tyres.