Science Buddies: "Ask an Expert"

I m doing my science fair project on the transfer of motion. I have built 3 Newton's cradles. Each cradle has 1in diameter balls made of different materials (1 rubber bouncing balls, 1 wooden balls, 1 foam balls). I am trying to show that different materials will affect the motion of the balls. Can you give me some guidance on putting everything together.

Newton's Cradle is a demonstration of the conservation of energy and momentum. The most common example uses metal balls as they will not deform when struck and will transmit a substantial amount of energy through the remaining balls. It is interesting that one of your models did not use steel balls as a comparative example. It should show a very different action than the other materials you have chosen. Each of those materials will absorb an amount of energy and transfer less with each collision.

A couple thoughts about your construction. The rails that suspend the balls should be rigid so they don't move counter to the balls motion as this will diminish your observed result. The balls should just touch one another so that there is minimum motion in the intermediary balls.

Rick Marz

Jackson- great experiment!

As you get started, be sure to check out these sites: they will help you develop a good background for the experiment.
http://www.lhup.edu/~dsimanek/scenario/cradle.htm
http://www.sciencedaily.com/articles/n/ ... cradle.htm

Adding on to Rick's post, one way to measure the conservation of energy throughout the system is by measuring height. Neglecting air resistance, the principal force guiding the motion is gravity. Gravitational potential energy is given by PE= mgh, where m is the mass of the first ball that you raise, g is 9.81 m/s^2, and h is the height above the system you raise it (so it's actually gravitational pot. energy relative to the other balls). When you let go of the ball and the last ball rises, measure its height. In an ideal elastic collision where mechanical energy is fully conserved, it should rise to exactly the same height. However, as more and more energy is lost to air resistance and the deformation of the balls, the less high it goes. You can thus test different types of balls using height as a dep. variable.

Don't be limited to this- it was just to start you off. Let us know if you have any more questions.

--Manjinder