Naked Science Forum

General Science => General Science => Topic started by: allan marsh on 05/02/2015 23:51:04

Title: How fast is force transmitted in an Newton's Cradle?
Post by: allan marsh on 05/02/2015 23:51:04

I was given one of this desk toy that consist five heavy metal ball hanging from an overhead rod.
You will have seem the four balls touching when the fith ball is allowed to swing against the touching group.
My question is...... How fast is the effect past from one ball to the last,noting they are all touching..... What is the shunting speed?

Title: Re: Swinging heavy metal balls
Post by: David Cooper on 06/02/2015 17:16:58

You want the speed of sound in metal then. I think from memory that it's four times the speed of sound in air if you're putting your ear to a railway track to determine whether a train is coming.

Title: Re: Swinging heavy metal balls
Post by: evan_au on 08/02/2015 06:20:27

The speed of sound in steel (http://en.wikipedia.org/wiki/Speed_of_sound#Three-dimensional_solids) is around 6000m/s.

This toy is called Newton's Cradle (http://en.wikipedia.org/wiki/Newton's_cradle) (or Newton's Balls)...

I was surprised to see that for it to work well, you need a small gap between the balls (of around 10-20μm).
This would slow down the speed of transmission compared to a long steel rod of the same length.

Title: Re: How fast is force transmitted in an Newton's Cradle?
Post by: wolfekeeper on 18/03/2015 14:43:00

No such gap is needed; it works fine when they touch.