On Target


  • 1

    Here are some of the materials you can use

    • index card or cardboard
    • marble
    • 1 medium-sized paper cup
    • paper clips
    • scissors
    • smooth line (9 ft. [2.7 m]) (fishing line or kite string)
    • tape (masking or duct)
    • target drawn on a sheet of paper
  • 2

    Prepare ahead of time

    • Have paper and a pencil ready to write down ideas and sketches as you design.
    • Think about moving things that might need to hit a target accurately. What are some moving things that need to hit a target accurately? (Golf ball, spacecraft)
    • Set up a target zone. Construct a zip line by running a line between two chairs. Make the line so it runs at an angle, from a high point to a lower point. Move the chairs away from each other and stretch the line so it is tight. Place a target at the lower end of the line.
    • TIP: A zip line is a line that starts at a higher point and ends at a lower point.


  • 3

    Think about the challenge

    • When will you need to release the marble so that it will hit the target?
    • Will the marble hit the target right away or will it roll a distance?
    • Will the marble roll in a straight line after it is released?
    • How will the marble slow down enough to hit the target?
    • TIP: When an object that’s already moving horizontally is dropped (like a marble dropped from a cup moving down a zip line), it travels in a curved path called a trajectory.
    • TIP: As the marble travels down the zip line, it builds up a forward speed. Once it’s launched, the marble will keep going at that speed until a force, such as hitting the ground, acts on it. A force can be an impact, weight, or pressure.
  • 4

    Think about and write down your ideas

    • How will you modify the cup so it can carry a marble down a zip line and drop it onto a target?
    • What parts of your design will be important in getting the marble to hit the target?
    • How will you remotely release the marble from the cup?
    • TIP: If you want your marble to hit your target, you will need to figure out a way to get the marble to release cleanly from the cup. Also, the timing of your release will be important.
  • 5

    Look at the materials

    • What materials will you use to make the handle that holds the cup on the line?
    • How will you attach the marble holder to the line?
    • What materials will you use to make a remote release device so you can drop the marble while the cup is in motion?
  • 6

    Modify the cup

    • Decide whether your marble will sit in the cup or outside it.
    • Decide how your cup will travel on the line and drop the marble on the target.
    • Cut the cup or attach a holder for the marble.
    • TIP: If your marble will ride inside the cup, you can make a cut in the cup so the marble can slide out. If it rides outside the cup, you can make a platform or shelf for the marble.
  • 7

    Design and build the remote release

    • Decide how you will tip the cup at just the right moment so that the marble can hit the target.
    • Choose the materials and build the release.
    • Attach it to the cup.
  • 8

    Design and build the handle

    • Decide how your cup will slide down the zip line. 
    • Choose your materials and build the handle.
    • Attach it to the cup.
  • 9

    Design and build the handle (continued) 

    • Think about how you will prevent the cup from tipping over as it goes down the zip line.
    • Modify the handle if needed.
    • TIP: To prevent your cup from sliding horizontally on the zip line and tipping over, try wrapping tape on both sides of the handle at the point it sits the zip line. This will anchor the handle on the line.
  • 10

    Get ready

    • Attach the cup onto the zip line. 
    • Position it at the high end of the zip line.
    • Drop the marble inside the cup.
  • 11

    Let it go

    • Release the cup.
    • Try to release the marble at just the right point.
    • Modify your release if it doesn’t hit the target. And try again!
    • TIP: If the marble doesn’t eject cleanly, try enlarging the opening or unblock the platform. Or place small rolls of tape in the bottom of the cup to act as a chute that guides the marble toward the opening. 
    • TIP: If the marble accidentally falls out of the cup or off the platform, try adjusting the tilt of the cup. 
    • TIP: If the marble misses the target, try releasing the marble before the cup is above the target. This can help because the marble is already moving forward along the zip line, and will keep moving forward as it falls. 
    • TIP: If the cup travels too slowly, try making the angle of the zip line steeper. 
  • 12

    Did you know?

    • Water on the Moon
      Are you hoping to take a trip to the moon someday? Finding water on the moon is very important to the future of human activity there. In 2009, NASA plunged a spacecraft named LCROSS into a crater to see if there was ice in the soil. The Cabeus crater is in one of the coldest locations on the moon and it was already sitting about one mile (2 km) deep in the surface. Scientists believed the chances of finding ice at the bottom of this deep, dark, cold place would be much better than finding it at the moon’s surface, where the sun shines brightly on the soil, vaporizing any ice. Were they right? Yes! Data sent back from LCROSS confirmed there is water ice in the lunar surface.
  • 13

    Try this next!

    • Time your marbles as they travel down the zip line. Try to send your marble down the zip line to the target in 4 seconds. Then 3 seconds. Then 2 seconds. 
    • Race with a friend and track the results. Have zip line races with a friend. Change the distance the marble has to travel, the steepness of the ramp, the size of the marble, or the size of the target. Graph your results.