The Marvellous Marble Drop

A) Objective: To introduce students to the concepts of gravity, ramps, angles, and friction by having them work in pairs to solve a fun and challenging problem. They must construct a marble drop course that spans 1 meter in exactly 10 seconds.

B) Time: 1-1.5 hr

C) Materials:

1. one half sheet of bristle board per pair of students.
2. scissors
3. masking tape ( of a limited amount)
4. a marble
   

D) Theory: Gravity causes all objects to fall at a speed of 9.8m/s². One factor that can affect the speed at which an object falls, or moves, is friction. Frictional force acts on an object, slowing it in the direction that it is moving. In this case a marble will be dropped, and the friction factor of the surface on which it will roll dictates the speed at which it will move. That is, a sticky or rough surface will slow the marble more than a flat, smooth surface. Another factor that affects the speed at which an object moves is the tilt of the surface on which it is moving. The higher the tilt, the faster the object moves. If the surface is tilted upwards the object will loose speed significantly as it proceeds.

E) Procedure:

1. Ask the students why things fall when they are dropped. This leads into a discussion on gravity.
2. Measure out a distance of 5 wall bricks (approximately 1 meter) and mark the top and bottom with a chalk line. The bottom line should be at least a foot away from the ground.
3. Show the students the marks on the wall, and explain that they will be challenged to design and construct a marble drop course that spans the marked distance . The difficult part is that the marble, once dropped from the top line, must take exactly 10 seconds to reach the bottom line.
4. Tell the students that they can only use the given supplies ( bristle board, tape, scissors). Discuss with them the concept of friction and have them come up with the idea of using tape sticky side up to increase friction. Discuss the angles at which the marble will roll the most slowly.
5. Talk about how to catch the marble at the end of the course, and have them design a container to catch the fallen marble.
6. Get the students into groups of 2 or 3 ( at the most) and have them start constructing. Make sure there is a timer on hand so that they can time their "drops" periodically.
7. Have a final "drop off" and see who came the closest to the 10 second goal.
8. To conclude this activity, talk about the time of each course, problems they faced, and possible suggestions and modifications for future courses.

G) Real Life Examples: Rollercoasters.

Check out the interactive java marble drop applet online