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Spaghetti Accelerometer

Science Snack
Spaghetti Accelerometer
Measure acceleration with spaghetti and marshmallows.
Spaghetti Accelerometer
Measure acceleration with spaghetti and marshmallows.

How does a car know when to deploy its airbags? How does a cell phone know when to rotate its screen? Tiny devices called accelerometers can detect external forces and changes in motion. Make a not-so-tiny model accelerometer of your own to understand how they work.

Tools and Materials
  • Three uncooked spaghetti noodles (plus extra in case of breakage)
  • Nine mini marshmallows (plus extra for eating)
  • Small wooden block, roughly 1.5 x 1.5 x 2 inches (4 x 4 x 5 cm) 
  • Drill with a 1/16-inch (1.6-mm) bit
  • Optional: cell phone with slow-motion video camera (not shown) 

Drill the wood block:

1. Drill a hole in the top center of the block. Then drill holes on two sides near the top of the block (click to enlarge the photo below). Be careful to drill the holes at different heights and away from the center to keep them from interfering with each other inside the block. Drill all the way through the block so you’ll be able to push through and remove any spaghetti noodles that break inside.

Make the accelerometer:

2. Slide a mini marshmallow onto one end of each strand of spaghetti. Hold each spaghetti noodle horizontally and make sure it bends down slightly from the weight of the marshmallow. If it doesn’t, add more marshmallows until it does.

3. Slide a strand of spaghetti into each of the three holes in the wooden block.

To Do and Notice

Set the block on a table and slide it along one of the axes of the spaghetti noodles. What happens to the spaghetti? What happens to the marshmallows? 

Now try moving the block up and down in a straight vertical line. Does each strand of spaghetti behave the same way as before? 

Hold the block so one of the noodles is standing straight up, vertically. Rotate the block 90 degrees so the standing noodle is now horizontal and one of the horizontal noodles is pointing down, vertically. What do you notice about the motion of the marshmallows?

What's Going On?

With every wiggle and jiggle, your spaghetti accelerometer shows you exactly when and how the block is accelerating—that is, changing speed or direction. 

According to Newton’s Laws of Motion, an object remains in motion (or non-motion) unless acted on by a force. This tendency is known as inertia. The more massive an object, the more force required to accelerate it. 

When you apply force to the block to move it, the marshmallows’ inertia causes them to stay in place until the force has time to travel from the block to the far end of the spaghetti. This time delay shows there’s an acceleration taking place: The lagging marshmallows appear to move in the opposite direction of the motion, indicating a positive acceleration (that is, the block is speeding up). 

When you stop the block, the marshmallows keep moving until the force from the block has time to travel through the spaghetti to stop them. This causes the marshmallows to lurch forward in the same direction as the original motion, indicating a negative acceleration, or deceleration (slowing down or stopping). 

You can find accelerometers in cars, cell phones, airplanes, flying drones, video-game controllers, and elsewhere. Modern electronic accelerometers are astonishingly tiny—just 500 micrometers, or 1/50th of an inch across. Though not made with marshmallows, they serve to detect changes in orientation and motion in much the same way as you see here.

Going Further

Use the slow-motion camera feature on your cell phone to take a video while a partner quickly starts and stops the accelerometer. Try moving the block along all three axes of the spaghetti. What differences can you see in the motions of the marshmallows? 

Some downloadable computer applications can directly access the accelerometers built into cell phones. Try comparing the data collected with one of these applications to the data collected with the spaghetti accelerometer. 

Teaching Tips

This activity is highly engaging, and participants are likely to have fun just wiggling the spaghetti around. Ask your students to think of the block as a cell phone and have them use it to describe what they think happens when they rotate their phone. For simplicity, you can build up this activity by first moving the block along just one axis, and adding the other two directions of movement one at a time.

Before doing this activity, have participants use the materials in front of them to design how they think their phone’s accelerometer works. This can give them the opportunity to think more deeply about the problem and imagine possible solutions. Encourage them to pay attention to how the direction in which each marshmallow is pulled down by gravity changes as they rotate the block. Making the connection between the marshmallows weighing down the spaghetti and the phone always knowing which direction is down will help participants to improve their models and their understanding of how the accelerometer works.

This is a good fit after students have learned about motion and forces. It offers a deep dive into inertia to help students better understand Newton’s Laws. This Snack can also be used as an engineering challenge, giving students an opportunity to design a better way to measure acceleration.

For younger students, make connections to things that they might experience but don’t think about often, like how, when riding in a car or a bus, they can tell when it changes direction or slows down, even with their eyes closed. This device allows cell phones to do the same thing.