Instructions for Building a Newton's Cradle

Cradle design

• Commercial versions of Newton̵7;s cradle usually have five steel balls hung at the same height from dual cross members on a rigid frame. The balls are suspended by two strings of equal length and angle from the overhead beams and hung far enough apart to just touch when at rest.

Design variations

• A cradle could be made with as few as three balls or as many as the designer has patience to align properly. The size and number of the balls make little difference in performance as long as they are matched in size and aligned properly.

Materials

• Wood or metal are generally used for the cradle̵7;s frame and base. Any material that is rigid enough to maintain alignment could be used.

  Steel ball bearings are usually used on commercial models of this toy. Golf balls, wooden spheres, high-bounce balls or even bowling balls can be substituted. As long as the balls have matching size and mass and the frame is strong enough to support their weight and maintain alignment, the builder can exercise their imagination.

Sample model instructions

• Build a frame 12-inches long, 10-inches tall and six-inches wide. Attach the frame to a 16 by 12-inch base.

  Thread one small screw eye into each of your five golf balls.

  Measure and cut 10 sections of braided fishing line 14-inches long.

  Tie two sections of line to each screw eye.

  Measure and mark the center of both 12-inch cross members.

  Tie one line from the first golf ball to each of the cross members at the center marks.

  The finished length of the line holding the ball to the cross member must be 10-inches.

  Working alternately to the left and right of center tie the remaining golf balls to the frame in the same fashion.

  When properly hung, the golf balls should just touch one another while hanging straight down.

Construction notes

• While selection of materials is not critical to the cradle̵7;s operation, precise measurements and construction methods are.

  The frame should be built on a solid base. Both cross-members should be at the same height and square to each other.

  The lines used to suspend the balls must be exactly the same length when finished.

  All balls must be exactly aligned in the center of the cradle at the same height.

  The correct operation of Newton̵7;s cradle depends on the exact alignment of all parts. A ball that fails to strike squarely in the center of its neighbor will not transfer its momentum properly.