Coefficient of Restitution of Water

[hgbreton]

I am doing my A level physics coursework on bouncing ball bearings off water. The basic set up is to fire a ball bearing of mass approx 10g and diameter 1cm out of an air gun at approx 20m/s and model its motion as it bounces off the surface of the water. Is it appropriate for me to be considering the coefficient of restitution of the impact of the ball with the water, seeing is water is a liquid not a solid? Or is there some more accurate way of modelling the impact? Any help would be greatly appreciated!

 

[jbsteele]

Yes, it is appropriate to consider the coefficient of restitution of the impact. The coefficient of restitution (COR) measures the amount of energy that is lost in an elastic collision between two objects. When a solid object such as a ball bearing collides with a liquid such as water, the COR can be estimated by measuring the ratio of the maximum height of the rebound to the initial height before the collision. This ratio will tell you how much energy was lost in the collision. Additionally, you can also consider the angle of incidence, which is the angle at which the ball bearing hits the surface of the water. This angle affects the COR and will help you accurately model the impact.

 

[nlightner]

I commend you for choosing to investigate the coefficient of restitution in your A level physics coursework. It is an important concept in the study of collisions, and your experiment with bouncing ball bearings off water will provide valuable insights.

To answer your question, it is appropriate to consider the coefficient of restitution in this scenario. While water is indeed a liquid and not a solid, the concept of coefficient of restitution can still be applied. The coefficient of restitution measures the elasticity of a collision, or how much energy is conserved in the collision. In the case of a ball bearing bouncing off water, the water may not be able to fully restore the energy of the ball bearing, but it still plays a role in the collision and can affect the rebound of the ball bearing.

In terms of a more accurate way of modeling the impact, there are various factors to consider such as the surface tension and viscosity of the water, as well as the shape and size of the ball bearing. It may be helpful to conduct multiple trials with different variables to get a more comprehensive understanding of the impact. Additionally, you may want to research and incorporate the concept of drag force in your analysis, as it can also play a role in the motion of the ball bearing through the water.

Overall, it is appropriate and important to consider the coefficient of restitution in your experiment with bouncing ball bearings off water. I wish you the best of luck in your coursework and look forward to seeing the results of your experiment.