Science Buddies: "Ask an Expert"

Hello,

My mother and I are trying to help my brother to do a science project that he was given in school, but we are not able to find any information in the internet on how to proceed. Can you please help us or guide us to what to do first and where can we find information about the following project.

How do concrete and ceramic tile affect the number of times a basketball will bounce.

Some of the questions include:

Bibliography

Please help!!!!!!

I would be happy to help. Lets start with the experiment itself.

You are going to want to start with the ball at a particular height. You are going to repeat this several times so you will want the height to always be the same but fairly high so that the ball has some good bounces. You might want to try several different heights to determine what height you believe will work best (you don't want too many bounces or too few). It would probably work easiest to have your brother stand on a chair (don't forget to hold on to him!).

From the specific height you have chosen, your brother will drop the ball. Don't have him throw the ball. If he throws the ball it will add an additional energy to it every time that won't be consistent. If he just drops the ball then the starting energy will always be proportional to the height of the ball times gravity.

Now have him drop the ball several times from this height on a cement floor and several times on a tile floor and count the bounces. Doing the experiment several times will account for any slight differences between measurements (bounces).

For the experiment that is all you will need to do. I should mention that there may be other variables which could change things. For example, if it is cold outside and the concrete is outside, the rubber on the basketball will be cold and it will bounce differently than on the tile inside. You will want to keep everything as close to the same as possible during the experiment. The only thing you want to have change is the floor that the ball will bounce on (use the same ball and make sure it has plenty of air in it). (Of course he can always do hardwood floors and such.) Also keep in mind that the tile floors have grouted areas and if the ball hits these it won't bounce the same and might not even go in the same direction!

So the basic physics of what is happening is rather interesting. There are two types of energy that you will be playing with. The first is potential energy. So when the ball is at some height it has the "potential" to fall because of gravity. The second is kinetic energy which is the energy something has when it is in motion. When your brother is holding the ball it has only potential energy because it is not moving. As it falls the potential energy decreases and the kinetic energy increases. At the floor the potential energy (for our purposes) is zero. The ball hits the floor and looses some energy to the floor. (This is the Newton law thing ... for every action there is an equal and opposite reaction ... however the floor is much much bigger than the wall so the energy lost to the floor is not visible.) The ball bounces off the floor and goes up. As it increases it loses kinetic energy and gains potential energy until it is at the top of the bounce. Then it happens all over again. So that the total amount of energy is conserved (when you include the energy lost to the floor). This is how roller coasters work!

So the energy lost to the floor is different depending on the type of floor and the ball will lose more or less energy and as a result will bounce either less or more, respectively! This is a very basic explanation and hopefully will be enough to guide you through the explanation to your brother. Of course we are always here if you need a little more guidance on the explanation part.

As for references (aka. bibliography):

The first one is for an actual science project to build a roller coaster. It is aimed at older students but it has good references at the bottom of the page and will give you a little more explanation of kinetic and potential energy.
https://www.sciencebuddies.org/science- ... p037.shtml

These two just present the ideas of potential and kinetic energy and one, in fact, talks about how to do a ball dropping experiment!
http://jersey.uoregon.edu/vlab/PotentialEnergy/
http://www.eia.doe.gov/kids/energyfacts ... nergy.html

Good luck and we are here if you need any more help!

Heidi

Just on a side note, the number of times a certain object bounces on a particular surface is related to the coefficient of restitution for that particular collision. If you're interested in reading more about this here is link which in and of itself contains some other helpful links at the bottom of the page. http://en.wikipedia.org/wiki/Coefficient_of_restitution

One problem that you may encounter is that it will difficult to count, at least with the human eye, how many total bounces there are at the end of the bouncing process because of the small distance and speed at which the ball might be moving. This is the reason why I have mentioned the coefficient of restitution; instead of measuring the time it takes for the ball to stop bouncing you could calculate the coefficient of restitution for the particular collision which will give you an idea of how "bouncy" the collision is. The idea is to measure the initial drop height and the height reached on the next successive bounce and then plug this into the formula given in the wikipedia article.The formula themselves are consequences of the principle of conservation of energy and the conservation of momentum, which Gizzmo described. Good luck. If you have any further questions feel free to ask!

Hi! A couple of more ideas:

1. Make sure that you drop the ball from the same height each time. You may want to put it on a shelf somewhere and just push it off (or put a piece of tape on the wall and place the ball so the bottom of the ball just touches the tape -- release the ball and make sure that it doesn't bounce off anything before it hits the ground.

2. Try it with multiple balls. Will a Super Ball make a difference? What happens if you give the ball a horizontal velocity?

3. You could try two or three heights and see how it makes a difference -- but you have to make sure that each time you drop a ball from a given height, you drop it from that exact height each time.

Good luck!

ACG

Hi,

I agree with the previous post, creating an experiment to test the effect of horizontal velocity on the number of bounces is another interesting variable to test. The only problem with this is that you would need a way to consistently apply the same force to an object to create this velocity.

Also, have you thought about using surfaces other than ceramic and concrete?
What about something like a rug, blanket, or a rubber mat?
Another interesting variable to test is how a thin layer of water (~1cm) in a large container will effect how much energy the ball loses after each bounce...