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# Tag Archives: dynamics

## Size of body neglected in Circular motion

Why in circular motion the size of the moving body is neglected?

Answer:

Not only in circular motion, but in entire kinematics we discuss the case of point objects only. In kinematics we study motion only and not the objects undergoing the motion.

A point object is an object having negligible dimensions compared to the distance travelled by it. For example, a car moving from Delhi to Mumbai can be considered a point object.

Further, when we discuss the concepts in Kinematics, even a large object is dealt considering the entire body to be a single point. This point will be the centre of mass of the body.

If a person is revolving a stone tied to a string, the centre of mass of the stone is taken for determining the length starting from the point about which it revolves.

In dynamics, we have to consider the shape and size of the body also.

## Question from Rotational Dynamics

**Dyana** Asked:

A small rubber wheel is used to drive a large pottery wheel. The two wheels are mounted so that their circular edges touch. The small wheel has a radius of 3.5 cm and accelerates at the rate of 7.9 rad/s^2, and it is in contact with the pottery wheel (radius 23.0 cm) without slipping.

a)Calculate the angular acceleration of the pottery wheel

b)Calculate the time it takes the pottery wheel to reach its required speed of 64 rpm

**Students and teacher visitors are requested to respond**