DIRECTIONS: Answer question 1 in pen before you turn over.
Scissors only, with a grown-up in the room. If a step seems to want a knife, snip or fold instead.
What you need: card · cardboard · marbles · masking tape · a paper towel tube · scissors · a ruler · a timer. Two marbles the same size.
The quickest way down is not the straight line. The curved ramp is longer, yet the curved marble wins: it does its falling at the start, then goes flat out.
Before you build anything: which do YOU think gets there first, and why? Then go and ask a grown-up the same question and write down what they said.
Two Ramps, Printed the Same
Making · Projects · Page 2 of 6
DIRECTIONS: Glue this page onto cardboard. Cut TWO of each shape: four pieces.
Both ramps start and end on the same two dots, or the race proves nothing.
The Race
Making · Projects · Page 3 of 6
DIRECTIONS: Five races. Swap the marbles over halfway, in case it is the marble.
Each ramp. Stand two matching pieces upright, half a marble apart, so a marble
rides on the two top edges. Tape card scraps between them at each end.
Start together: hold both marbles behind a ruler at the top and lift it
straight up. No pushing.
Race
Which marble was on the curve
Which arrived first
By a lot or a little?
1
2
3
4
5
If the straight ramp wins, check the setup: ramps upright? dots at the same height and place? anything catching? both let go at once?
Why, and the Rule It Gives You
Making · Projects · Page 4 of 6
DIRECTIONS: Read this after you have raced them.
Speed comes from how far you have dropped. The curve drops early, so its marble is fast almost all the way. This curve (traced by a point on a rolling wheel) is the fastest path there is.
In 1696 Johann Bernoulli set this as a challenge. Isaac Newton solved it in
one night and sent it back unsigned. Bernoulli: "I recognize the lion by his claw."
A marble never climbs back to where it started: rubbing takes some of the drop. So every hill must be lower than the one before.
Rubbing means a hill just below the line fails too. Build by the stricter rule:
every hill lower than the one before.
A Real One, Down a Door
Making · Projects · Page 5 of 6
DIRECTIONS: Build it all, starting with a steep drop. Then test and fix one piece at a time.
Do this
How
Why
Cut the tubes in half the long way
Squash the tube flat, cut along one fold, open it out, cut along the other. Two half-pipes from one tube.
A whole tube hides the marble. Half a tube shows you exactly where it went wrong, which is the only way to fix anything.
Tape it to a door, top to bottom
Masking tape, two strips per piece, and press hard. Start at the top and work down.
A door is flat, tall, free, and you can take the whole thing off afterwards. Masking tape comes off paint; other tape does not.
Overlap each piece INSIDE the one below
The top of the lower piece goes underneath the bottom of the upper one, by about an inch.
Butt them end to end and the marble hits the lip and stops. Overlap the wrong way and it launches into the room.
Every drop lower than the last
Work down the door and never go back up.
Page 4. It cannot climb higher than it started, and it is lower than that already.
Corners cost you
Sweep them wide. A tight corner throws the marble up the outside wall.
Going up the wall is going uphill, and everything it spends climbing it does not get back.
Put a box at the bottom
A shoebox on its side, or a bowl.
Otherwise the marble goes under the sofa and this is the last time anybody plays with it.
Start steep, so the marble is fast for the rest of the run.
What You Found Out
Making · Projects · Page 6 of 6
DIRECTIONS: Run still on the door.
Look back at your prediction on page 1, and at what the grown-up said. Were either of you right? What had you both been assuming?
One place on your run kept failing. Where was it, and what did you change in the end?
Time the marble down the whole run. Now make ONE change and time it again. What did you change, and did it help?
Somebody says: “make the whole run steeper and it will be quicker.” Using what you found on page 3, say what is right about that and what is wrong with it.