Materials

• large steel ball
• 1 track section
• 1 board
• 1 wood block to prop up ramp
• 3 white plastic strips
• tape
• 3 sticky arrows

Here's a puzzle to solve: Make a rolling ball follow a course and hit a target.

To do this, use a ramp propped on one wood block to start a ball rolling across a large flat surface -- a table or the floor. You will need about 1 m meter square. Tape the ramp in place and don't move it for the rest of the challenge.

Lay out a course for the ball on a table or smooth floor. Place the three sticky arrows about 50 cm (18 inches) apart, not in a line, and pointing various directions. Then figure out how to make the ball move around so that it goes over each arrow in the direction of the arrow.

Tape the plastic strips to the table, standing them up like short walls, straight or curved in any shape that you like, to change the direction of the rolling ball.

Rules:

• The ball must touch each course marker in order, in the direction the arrows indicate.
• After you release the ball on the ramp, it can only touch the ramp, table, and plastic strips (and course markers and target)
• You may not move the table or introduce other external forces on the ball. Once you have found the right arrangement, the motion should be completely reproducible, so that after the ball is released (from the same place on the ramp) it follows the same path.
• Moving or turning the arrows is not allowed!

1. Draw a top-view diagram of your successful course. Show where the ramp is, where you put each plastic strip and its shape, where there are no strips, and where your target is. Draw a dotted line showing the path of the ball through your course.

2. Explain what you use the plastic strips for.

3. Describe the motion of the ball when it is not on the ramp and not touching a plastic strip.

4. Could we make a ball go in an S-shaped path with just one strip? Make a top-view drawing that shows how the ball would move. Explain why it moves that way.

Check the box when you are done: