## Materials

• marble
• Stuff to build the marble run with: cereal boxes, paper towel or toilet paper tubes, paper cups, and so on. Try to use all recyclable materials.
• scissors
• raised surfaces (such as a wall, shelf, table, and/or chair) to build the marble run against
• a stopwatch or timer

## Instructions

Most of the time we work to make things go really fast—faster cars, planes, phones, and more. But for this challenge, we’re interested in exploring what it takes to slow things down.

We challenge you to design a marble run that makes a marble move as slowly as possible.

There are 3 constraints for this challenge (an engineering constraint is a limitation on your design):

• The marble has to keep moving through the entire run.
• The run needs to change directions at least 3 times.
• It must take a minimum of 10 seconds for the marble to travel the whole track.
• Brainstorm Designs

As you work through possible designs, think about what you know about:

• Friction—a force that slows things down when they rub against each other.
• Gravity—a force of attraction that pulls everything toward the center of the Earth.
• Drag—a force that happens as things move through air or water, which causes friction.
• Momentum—a force that makes things keep moving once they’ve begun.

Explore:

• How can you increase friction to slow the marble’s momentum?
• If a steep incline makes a marble pick up speed, what happens if the slope is barely noticeable?
• What kinds of surfaces might cause drag and slow the marble down?
• Experiment with the materials you’ve collected. How can different lengths of track affect a marble’s speed?
• How does changing the marble’s direction impact its speed? Remember—you need to do this at least 3 times in your run.

Build

• You’ll need to figure out what you will build your marble run on, such as pieces of furniture, a wall, a big piece of cardboard or poster board. Whatever you decide, make sure you get permission before you start.
• Put your marble run together by using the design you sketched.
• You might want to build out a few pieces at a time so you can adjust as you go. As every engineer knows, what looks great on paper doesn’t always work out once you’ve started actually building!

• Set your timer for 10 seconds. Your goal is to make the marble take at least that long to roll through the run.
• Put your marble through the run. Watch carefully: where does it speed up? Where does it slow down? Does it pause anywhere, like at a point where it drops to head in a new direction?

Evaluate and Redesign

• Did your first design work as planned? Engineers hope for that result but know that it rarely happens. There is almost always something that can be redesigned to work better.
• Did your marble stop before it reached the end of the run? How can you adjust the design to keep it rolling?
• Did your marble speed up too much through a particular section? What if you put some kind of material along the bottom of the track that creates friction and slows the marble down?
• Would adding speed bumps help to slow the marble down anywhere?

Make Change and Try Again!

• See if you can make the marble move even more slowly through the run.
• If this design challenge was easy, ramp it up. Can you make a longer run and keep the marble moving slowly? What about building a marble run that sets off a domino run or other chain reaction?

Share Your Results with a Teacher, Parent/Guardian, or DiscoverE!