Today we are tackling a really cool STEM project building a Newton’s Cradle. We will explore the Newton’s Cradle and how it works, then build our very own that students can show off to their family and friends. This project builds skills in engineering, science and math. It is perfect for upper elementary and older students.

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## What is a Newton’s Cradle?

I’m sure you have come across this amazing scientific device. A Newton’s Cradle has five or six shiny silver balls hanging in the middle of two frames. When you pull either one of the balls on the end backward and let it go, this ball hits the ball next to it, causing each of the balls to hit the next ball until all the balls are swinging, almost like a pendulum on a clock, moving from left to right and then stopping.

Building a Newton’s Cradle is a fun physics project for entertainment, school, or even a science fair. It is made of mostly recycled materials you will probably have at home or at school. Let’s look at the science of it all first.

## The Science of Newton’s Cradle

The scientific principles of this device were first shown by a French physicist called Abbe Mariotte in the 17th century, but it didn’t have a name until Simon Prebble called it a Newton’s Cradle in 1967. He wasn’t a scientist or a physicist but an actor. He made his version completely out of wood. In later years, they were made with steel balls and started being sold as executive toys.

Sir Isaac Newton, a famous scientist and physicist, devoted his life to studying momentum, the force or speed of an object in motion and energy. The Newton’s Cradle demonstrates two of his Laws of Motion.

Want to learn about Newton’s First Law of Motion: Inertia? Check out this Pendulum Painting Project!

### Newton’s First Second Law of Motion: Force

The acceleration of an object depends on the mass of the object and the amount of force applied.

This means that the force you use to push something and the object’s weight or mass is responsible for how fast the object moves or accelerates. Imagine pushing your little brother on a swing at the park and then pushing your father on the same swing with the same amount of force. Because your little brother weighs much less than your father, he will move at a greater speed and go higher than your dad.

### Newton’s Third Law: Action & Reaction

For every action, there is an equal and opposite reaction.

This means that when you push or pull an object, it moves or pulls back on you with the same force you used on it.

### Conservation of Momentum and Conservation of Energy

The other two principles used in this device are the Conservation of Momentum and the Conservation of Energy.

##### Conservation of Momentum

When you lift and let go of the marble on the end, it hits the next ball, transfers its energy onto this ball, and almost stops completely. All the marbles are the same size and weight, and the process is repeated with all the marbles, and no energy is lost in the process. This means that the momentum or speed of the marbles in motion remains the same throughout the process.

##### Conservation of Energy

Energy gives objects the ability to move. On Newton’s Cradle, when you raise the first marble and let it go, it has potential energy or stored energy, making the other marbles move in the same way because of how high you lifted it. When you let it go, it hits the next ball. As it does this, it converts the potential energy into kinetic energy, the energy of motion.

This energy is then transferred to the next marble and the next in a wave. The last marble receives most of the initial energy from the fall of the first marble, causing it to swing upward to the same height as the first ball started at.

The material of the marble has good “elasticity” (the ability to bounce back when pushed), so Newton’s cradle works perfectly.

Other materials, such as steel or wood, are also suitable. These materials can store kinetic energy as potential energy when they are manufactured.

Let’s make a Newton’s Cradle to understand all this!

## DIY Newton’s Cradle Video Tutorial

Although this project has lots of steps it really is not that complicated and the best way to see how easy it is to do this project is to watch our video tutorial. If you can’t see the video below, it is being blocked by adblockers or a firewall. You can also view this video in higher quality and with closed captioning, on the STEAM Powered Family YouTube Channel.

## Materials & Tools

Ruler
Scissors
6 Medium-thickness wooden skewers or chopsticks
Pencil
Box cutter
Thin corrugated cardboard (an old box will do)
Sandpaper
BluTack
Fine thread or cotton or dental floss or fishing line
4 paper towel tubes
6-8 Marbles – all need to be the same size, slightly larger is better
Pliers
Side cutter
Awl or nail
Compass
Glue gun
Rapid drying Epoxy
Sand (any sand will do, it is simply to weigh down the corners)
Paint or felt-tip pens and stickers or colored paper to decorate your Newton’s Cradle

Start by preparing all the skewers, tubes, and cardboard circles.

Using a ruler and a pencil, mark, measure, and cut the wooden skewers using a side cutter. You will need:

• 4 pieces that measure 17cm.
• 4 pieces that measure 10cm.

Make marks at 1cm from the ends of all the skewers you cut.

Measure the height of all the tubes. They should be 20cm tall. If you need to cut them shorter, use the box cutter.

Safety Note: Box cutters are sharp. Responsible adult supervision is required at all times. For younger students, an adult should do all of the cutting.

Measure the diameter of the tubes by using a compass. Then make 8 circles on the corrugated cardboard that are 5mm bigger than the diameter of your tubes. Cut the circles out with scissors. The tubes I used had a diameter of 4cm, and I cut my circles 4.5cm in diameter.

PRO TIP: Cut each circle close to the top and bottom of the circle you drew so it looks like a square. Then trim off the rounded edges; you should have a perfect circle!

Cut 6 lengths of thread to a length of 30cm.

### Prepare the Marbles

Push 6 marbles into 6 pieces of Blu Tack onto the surface you are working on. Then grab 6 wooden beads, sandpaper, and pliers.

Hold a bead with the pliers and lightly sand the bottom of the bead on the sandpaper. Repeat for all of the beads.

Mix a small amount of Epoxy on a scrap piece of paper or cardboard and pick one of the beads up with the flat side at the bottom. Dip the flat side into the Epoxy and gently place it on the top of the marble. Repeat with the other beads and marbles.

### Prepare the Tubes

Let’s make marks and holes on each of the tubes. This part can be confusing until you see what we are doing to build a perfectly symmetrical frame. The best thing to do is watch the video. Once you see the process it is so much easier to do it yourself. Plus, you don’t want to get all the pieces together with the glue gun only to realize that it is wrong and that you must take it all apart!

First, make sure you have a ruler with a flat end. If you don’t, you can use a protractor. We must ensure that the lines we draw are 90 degrees to the surface you are working on.

Place your first tube upright onto the surface you are working on. Place the ruler up the side, and make a straight line with a pencil from bottom to top.

Make a mark on this line top and bottom, 1cm from the edge. This is where the holes for your skewers will be. Repeat this step on all the other tubes.

To make the holes, use an awl or a nail to make the first hole. Then, use the point of the pencil to make it a little bigger, and check that the skewer fits tightly into the hole. Repeat this step on all the other tubes.

#### Creating the 90 degree offset for perfect symmetry

Place a piece of paper in front of you, on the table and trace the circle at the bottom of the tube with a pencil. Wait to lift the tube up. Mark the paper where you made the first hole.

Using a ruler, make a vertical and horizontal line at this mark and check that this “cross” is in the middle of the circle. These lines must go out of the circle.

Place the tube over the circle and line up the hole you made with the line that runs vertically through the circle. Keep holding the tube and mark the horizontal line through the circle on the right. See the photo below:

Now draw the straight lines for the inner holes onto all the tubes with the ruler, from bottom to top. Make all your 1cm marks from each edge to place these inner holes too. Use the awl, pencil, and skewer method to make your inner holes the same way you made them before. If this is confusing, make sure you watch the video! It really helps to see the process.

### Prepare the Frame

Get all your tubes, cardboard circles, and skewers.

Take a tube and one of the long skewers you cut earlier. Push the skewer into the top hole and stop at the 1cm mark you made on the skewer. Using the glue gun, glue it in place on the inside of the tube.

Glue a second, long skewer into the bottom hole the same way.

Repeat this step with a second tube. The two tubes should look the same.

Place the two tubes down in front of you. The tube on the left must have long skewers facing outward to the left and the inner hole facing upward. The tube on the right must have long skewers facing outward to the right and the inner hole facing upward.

Starting with the tube on the left, place another tube on top of the first tube, line up the holes, push the skewers into the holes 1cm, and ensure that the inner holes face inward. Glue these to stick in place.

Put this whole piece down with the inner holes facing upward.

Repeat this step with the last tube. Place the two sets of tubes next to each other with the inner holes facing upward. They should look the same! Hang in there! We are almost done putting it together!

Glue the four short skewers into the four inner holes of one of the pieces and then glue this to the second piece left on the table.

Using the glue gun, glue a cardboard circle onto the top of one of the tubes. To get it centered, I put the glue first onto the end, turned the whole thing upside down, and placed it onto one of the circles.
Repeat this step for the other three tubes.

Turn the whole thing upside down and get the sand you will use.

Fill each tube with sand to “almost” the tops of the tubes and close each tube with the other four cardboard circles.

The frame is done!

## Hanging the Marbles on the Frame

Placing the marbles onto the frame can be a bit tricky. See the pictures below of how to do this or watch the video to see us doing these steps.

Cut a thin strip of paper that fits between the tubes. Make a mark in the middle of the strip. Place a marble on the strip and make a mark on either side.

Measure the length of the space. This is for the spacing of the marbles.

Make all the marks for the six marbles on the strip.

Transfer all the marks from the strip onto the two long skewers.

Don’t throw this strip of paper away!

#### Prepare the Marbles with Beads and Strings

Now we are going to get the marbles with the beads and strings ready.

Place a big piece of Blu Tack in front of you.

Push a marble with the bead stuck on it into the Blu Tack. The hole in the bead should face the left and right, not you.

Thread the thread through the bead. Pull the two sides upward so that both sides are the same length.

Tie the two sides together and pull down to the top of the bead. Push the two strings into the Blu Tack so that it is tight.

Put a tiny bead of hot glue onto the thread on the top of the bead. Let the glue harden before removing the marble from the Blu Tack. You don’t want the thread to loosen because you are in a hurry!

Repeat this step for all the marbles.

This is a good time to paint and decorate your Newton’s Cradle. If you paint over the marks you made for placing the marbles, it’s not a problem; get your paper strip and do them again!

All done decorating! It’s time for the last step……gluing the marbles onto the frame!

#### Gluing the Marbles onto the Frame

Place the string of the first marble onto and over the frame with about 1.5cm hanging over the outside of the frame.

Hold it tight in place and use the glue gun to put a small bead of glue over the string on top of the skewer. Remember to keep your fingers away from the hot glue. If you need an adult to help you, ask.
Again, let the glue harden before removing your fingers. You don’t want the thread to loosen because you are in a hurry!

###### All the other marbles must be at the same height. This is very important!

Repeat the gluing step with all the marbles on this side of the frame.

When all the threads are glued on this side, turn Newton’s Cradle around so you can see down the middle of it.

Take the thread of the first marble up to the other skewer and place the thread onto the mark you made on the opposite side of the frame. Keep pulling the thread until the marble hangs between the two sides equally. When you are sure it is in the middle, put a tiny bead of glue onto the thread to keep it in place.

Turn the whole thing around to stick all the remaining threads in place. Repeat the gluing process for all the remaining marbles.

To get all the marbles to hang at the same height and in a straight line, either loosen the threads or pull the threads gently toward you until you are happy with the positioning. Keep checking that every marble is hanging correctly and just touching each other. If things are not right, gently pull the thread upward from the bead of glue. The thread will come away with the bead easily. Sometimes, the bead remains on the skewer but will easily come off with the pliers.

PRO TIP: Do not cut the extra thread hanging off the skewer until you have tested your device and it is in good working order!

Here are some interesting questions and answers that you will find interesting and challenging:

#### Why do Newton’s Cradle balls eventually stop moving?

As the marbles on either end swing, the balls lose energy due to air friction, the sound they make, and the heat generated when they hit each other. Because the marbles lose energy throughout the process, their kinetic energy and momentum are reduced to zero, which slows the balls down and causes them to stop.

#### If the marbles get tangled, how do you untangle them?

While using Newton’s Cradle, there is always a chance that the threads can get tangled. Is there an easy way to untangle them? There is no solution to this, and it can be very frustrating. A whole lot of patience is needed! Here is a method you can try:
Turn the device upside down or on its side and rest the balls on the table. This prevents gravity from pulling the balls down and making the knots tighter.

Use a needle to help you untangle the knots. Start with the marble furthest away from the tangle. Work with one marble at a time, passing it through the loops it got tangled in. Pass it through and repeat this step. Trying jiggling the marbles around occasionally can also help unknotting the tangle. If you can’t untangle it, cut the threads, add new ones, and start again!

#### How can I make Newton’s Cradle run longer?

You can increase the running time of Newton’s Cradle by making the strings longer or using bigger marbles. This increases the device’s potential energy and causes the balls to swing for longer.

You could also try balls that bounce more, like small bouncy balls or Ping-Pong balls. These balls are made with material that has more “elasticity.”

You can test this theory by removing the marbles and replacing them with bouncy balls or Ping-Pong balls. You would have to find a way to attach the thread to them.

## More Extension Ideas

What would happen if the strings were shorter?

What happens when you pull two balls or three at a time instead of one on the end and let go?

How does the cradle work differently if you use steel balls, wood balls, or balls made of other materials?

I hope you had fun making Newton’s Cradle! Now, have fun exploring all the possibilities of this amazing device!