INTRODUCTION
This experimental project is aimed at applying analytical and experimental techniques to develop an understanding of the coefficient of restitution. The coefficient of restitution of a variety of balls will be estimated by allowing them to free-fall on a massive steel base.
EQUIPMENTS
• Balls
• Measuring tape
• Stop watch (use mobile phone if necessary)
Theory
The coefficient of restitution is defined as the ratio of speeds of a falling object, from the instance when it hits a given surface to when it leaves the surface. A ball is usually a round or spherical object used mostly in sports and games. Balls are made from a number of materials but leather, rubber and synthetics are the most commonly used materials.
Balls have their presence from a long time and been a part of almost all civilizations history. A type of game using a ball is portrayed on early Egyptian monuments. Each spring two large groups of people representing their gods acted out a contest using a round wooden ball and crooked sticks. The motive was to carry the ball through the opposing goal.
Procedure
Take the ball and hold it at a set height above the surface.
Drop the ball and record how high it bounces.
Repeat for a fixed number of trials.
Repeat with various balls.
tennis ball
golf ball
plastic ball
Glass marble
billiard ball
Steel ball bearing
wood ball
rubber band ball
Estimate the rebound heights and “flight times” (i.e. the time between rebounds)
Use you experimental data to estimate the coefficient of restitution of each ball using the height ratio method and the “flight time” ratio method.
Calculations
Coefficient of Restitution = speed up / speed down.
To determine the speed, measured average height is used in the formula, v = ?(2gh)
Here,
v = velocity,
g = 9.8m/s2
h = average height measured.
Coefficient of Restitution = ?(2gh)) / ?(2gH) = ?(h/H)
Sources of Error
Due to uneven ground the ball may not bounce straight up and hence the ball may not reach its peak height.
While releasing the ball from your hand, the ball may rotate slightly due to which some of its translational energy is lost and the ball do not bounce as it should.
