Spin Impact and Elasticity By Dr Ajay Kumar

Spin Impact and Elasticity By Dr. Ajay Kumar Reader School of Physical Education DAVV Indore

Definition & Types of Spin l Rotation around any axis is known as spin. l Rotation around horizontal axis is known as topspin or back spin. l Rotation around vertical axis is known as side (left or right) spin.

Cause of Spin l The cause of spin is the application of off center force. l The off center force is the force which does not pass through the center of gravity of the implement. l Due to spin the path of the ball also changes because the ball is moving in air, so aerodynamics effect is also a factor which is to be studied.

Properties and Nature of Spin l A ball moving through the air will also move in the direction of least air pressure. l If the ball is spinning it will follow a curved path. l Ball with top spin drop sooner than the ball with no spin. l A ball with back spin will move in an upward curve and thus stay aloft longer than a ball with no spin.

Properties and Nature of Spin (Cont) l Balls spinning around a vertical axis have side spin. l Right spin causes the ball to curve to the right and occurs when the forward edge of the ball moves to the right. l Left spin is the opposite of right spin. l The amount of the air a ball drag with it when spinning is depends upon the surface of the ball and speed of the spin.

Properties and Nature of Spin (Cont) l Rough or large surface, small mass and a fast spin speed will all produce a more noticeble spin and curve deflection. l The small mass of a table tennis ball, fuzz on a tennis ball and the seams on a baseball enhance spin. l The deflection will also be more pronounced if the forward velocity is slow.

Properties and Nature of Spin (Cont) l Spin on a ball may also smooth its flight by acting as a stabilizer. l The first and foremost use of the spin is spin provide accuracy. l Spin also change the rebounding properties of the ball.

Example l Spin in Table tennis l Spin in Tennis l Spin in Cricket l Spin in Volleyball l Spin in Baseball l Spin in Discus l Spin in Javelin l Spin in Football l Spin in Basketball

Impact and Elasticity l The nature of impact is governed by – Elasticity – Mass and velocity of the rebounding surface – The friction between the surfaces – The angle with which one object contacts the seconds

Momentum and Collisions l Momentum helps us understand collisions/ impact l Elastic Collisions - objects rebound l Inelastic Collisions - object stick together and usually become distorted and generate heat

Elasticity l Any time two or more objects come into contacts with each other some distortion or deformation occurs. l Whether or not the distortion is permanent depends upon the elasticity of the interacting objects. l “ ELASTICITY IS THE ABILITY OF AN OBJECT TO RESIST DISTORTING INFLUENCE AND RETURN TO ITS ORIGINAL SIZE AND SHAPE WHEN THE DISTORTING FORCE ARE REMOVED. ”

Elasticity (Cont) l The force which acts on an object to distort is called ‘stress’. l The distortion which occurs is called ‘strain’ and it is proportional to the force causing it. l Stress may take the form of tension, as in the stretching of a spring, compression, as in the squeezing of a tennis ball, flexion, such as the bending of a fencing foil, or torsion, as in the twisting of a spring.

Elasticity (Cont) l In all the previous case the objects tend to resume its original size and shape when the stress is removed. l If the stress is too large the elastic limit of the object a permanent distortion occurs.

Elasticity (Cont) l The material such as rubber seems highly elastic since it yeilds easily to a distorting force and returns to its original shape. l Actually, substances which are hard to distort and return perfectly to their original shape are more elastic. l Gases, liquids highly tempered steels are examples.

Elasticity (Cont) l In comparing the elasticity of different substance, coefficient of elasticity are used. l A coefficient of elasticity or restitution is defined as the stress divided by strain. l The coefficient of elasticity most commonly determined in sports for a ball is