Newton's Cradle
When you lift one ball and let it go, the energy travels through all the resting balls and launches the one on the far end. It is one of the coolest ways to see Newton's laws in action.
This build takes patience. Getting all six balls perfectly level at the end is the hardest part, so take your time with step 10.
What you will learn
- First Law: a ball sitting still stays still until something pushes it. A ball that is moving keeps moving.
- Third Law: every push has an equal push back. The ball that hits passes along exactly as much force as it received.
Learn more (optional):
Parts you need
- 1 cradle baseplate
- 2 cradle arches
- 2 cradle supports
- 6 ball bearings
- 6 ball bearing clamps
- 6 fishing line clamps
- 5 ft fishing line
Build steps
Step 1 - Connect the two supports to one arch
Slide both cradle supports into the slots on one arch. They should sit snug and flat.
Step 2 - Attach the second arch
Press the second arch onto the open ends of both supports to finish the rectangular frame.
Step 3 - Stand the frame up and slot it into the baseplate
Turn the frame upright and press the feet of both arches into the slots on the baseplate. The frame should stand on its own without tipping.
Step 4 - Clip each ball bearing into a bearing clamp
Press one ball bearing into a bearing clamp until it clicks in place. Do this for all six ball bearings.
Step 5 - Thread a piece of fishing line through a fishing line clamp
Thread one end of the fishing line through the hole in a fishing line clamp and leave a short tail sticking out.
Step 6 - Push the clamp onto the arch
Press the fishing line clamp down onto the top of one arch so it grips the arch and holds the line in place.
Step 7 - Loop the fishing line through the bearing clamp twice
Bring the fishing line down and loop it through the bearing clamp two times. Two loops keep the clamp from sliding along the line.
Step 8 - Secure the other end of the fishing line
Thread the free end of the line through a second fishing line clamp and press that clamp onto the arch on the other side, the same way you did in steps 5 and 6. Pull the line snug before you clip it down.
Step 9 - Repeat for all six ball bearings
Do steps 5 through 8 again for each of the remaining five ball bearings until all six are hanging between the arches.
Step 10 - Adjust all six bearings to the same height
This is the most important step. Slide the fishing line clamps up or down until every ball bearing hangs at the same height and they all line up in a straight row, just barely touching each other.
Take your time here. The cradle only works properly when all the balls are level and lined up.
Try it out
Lift one ball to the side and let it go. Watch what happens on the other end. Now try lifting two balls at once.
What to notice
- When one ball hits, only one ball swings out on the other side, not all five.
- The middle balls barely move even though the force passes right through them.
- The cradle keeps swinging for a long time because the balls pass energy to each other without losing much of it.
If something does not look right
- Balls are at different heights: open the clamp on the low or high side and slide the line up or down, then clip it again.
- Balls are not touching: slide the whole line left or right before clipping it back down.
- Frame is wobbling: push the arch feet more firmly into the baseplate slots.