Newton's cradle, named after Sir Isaac Newton, is a device that demonstrates conservation of momentum and energy
using a series of swinging spheres. When one on the end is lifted and
released, it strikes the stationary spheres; a force is transmitted
through the stationary spheres and pushes the last one upward. The
device is also known as Newton's balls or Executive Ball Clicker.
A typical Newton's cradle consists of a series of identically sized
metal balls suspended in a Plastic frame so that they are just touching
each other at rest. Each ball is attached to the frame by two wires of
equal length angled away from each other. This restricts the pendulums'
movements to the same plane.
If one ball is pulled away and is let to fall, it strikes the first ball
in the series and comes to nearly a dead stop. The ball on the opposite
side acquires most of the velocity and almost instantly swings in an
arc almost as high as the release height of the last ball. This shows
that the final ball receives most of the energy and momentum that was in
the first ball. The impact produces a compression wave that propagates
through the intermediate balls. Any efficiently elastic material such as
steel will do this as long as the kinetic energy is temporarily stored
as potential energy in the compression of the material rather than being
lost as heat.
With two balls dropped, exactly two balls on the opposite side swing out
and back. With three balls dropped, three balls will swing back and
forth, with the central ball appearing to swing without interruption.
Christiaan Huygens used pendulums to study collisions. His work, De Motu Corporum ex Percussione (On the Motion of Bodies by Collision) published posthumously in 1703, contains a version of Newton's first law
and discusses the collision of suspended bodies including two bodies of
equal mass with the motion of the moving body being transferred to the
one at rest.
The principle demonstrated by the device, the law of impacts between bodies, was first demonstrated by the French physicistAbbé Mariotte in the 17th century. Newton acknowledged Mariotte's work, among that of others, in his Principia.
Newton's cradle can be modeled with simple physics and minor errors if
it is incorrectly assumed the balls always collide in pairs. If one ball
strikes 4 stationary balls that are already touching, the
simplification is unable to explain the resulting movements in all 5
balls, which are not due to friction losses. For example, in a real
Newton's cradle the 4th has some movement and the first ball has a
slight reverse movement. All the animations in this article show
idealized action (simple solution) that only occurs if the balls are not touching initially and only collide in pairs.
There is much confusion over the origins of the modern Newton's
cradle. Marius J. Morin has been credited as being the first to name and
make this popular executive toy. However, in early 1967, an English actor, Simon Prebble,
coined the name "Newton's cradle" (now used generically) for the wooden
version manufactured by his company, Scientific Demonstrations Ltd.
After some initial resistance from retailers, they were first sold by Harrods
of London, thus creating the start of an enduring market for executive
toys. Later a very successful chrome design for the Carnaby Street store
Gear was created by the sculptor and future film director Richard Loncraine.