Newton’s Cradle


Download video below
Download video below

Suspended balls transfer momentum from one to the next.



Principles Illustrated

Conservation of momentum and energy, collisions, impulse.

Download video (right-click and “save link as”): Newtonscradle.m4v

NCEA & Science Curriculum

PHYS 2.4


Wait until the balls have stopped moving, displace one end ball and release. Displace two balls and release, etc. Quite interesting behaviour results that can be explained in terms of the need to conserve both momentum and energy. For example, one ball in and two out at half the speed would conserve momentum but not kinetic energy. A number of possible solutions for swinging one ball would conserve momentum, and a number would conserve kinetic energy. But not both.

Try swinging two balls at once, or three. Or two from one side and three from the other simultaneously. Or try a small bit of Blu-Tack to stick two of the balls together. What effect does that have?


Individual teachers are responsible for safety in their own classes. Even familiar demonstrations should be practised and safety-checked by individual teachers before they are used in a classroom.

Related Resources

Collisions between carts of equal mass on an air track or pucks of equal mass on an air table.

Teaching Resources

Would you like to contribute lesson suggestions? Contact us.


PIRA 1N30.10


This teaching resource was developed with support from

The MacDiarmid Institute
Faculty of Science, Victoria University of Wellington
School of Chemical and Physical Sciences, Victoria University of Wellington


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