Build a marble run with pipe insulation

Marble Machine is built on real physics. This activity lets you build a real marble run and check the game's ideas for themselves: height turns into speed, marbles cannot climb higher than where they start, and loops need a high start. It takes 30–45 minutes.

The big ideas

• Height is stored energy. Falling turns it into motion.
• Energy changes form, but the total stays the same. A little goes into heat through friction.
• A marble cannot climb higher than its start.
• A loop needs enough speed at the top, so it needs a high enough start.

What you need

• Foam pipe insulation (the cheap tube from a hardware shop), cut in half along its length so it makes a groove
• Masking tape
• Marbles of the same size
• A metre stick or tape measure
• A stopwatch (a phone works)
• A wall, a table edge or some books to build ramps on
• Optional: a larger ball, a hollow ball, and cardboard for supports

Safety: marbles are a choking hazard for children under 3, so keep them away from younger siblings. Pick up any marbles that roll away, as they are also a slipping hazard.

Activity 1: Height and speed

1. Tape one length of foam groove to a table edge or books so that it makes a slope that ends on a flat floor or table.
2. Mark the starting point on the ramp. Measure its height above the floor, and mark a finish line 1 metre from the bottom of the ramp.
3. Release a marble (don't push it). Time how long it takes to cross the 1 m after the ramp bottom. Do this 3 times and find the average.
4. Raise the start by 10 cm and repeat.

Calculate: speed = 1 m ÷ time. Make a table with start height and speed.

What to expect: higher starts give faster marbles. Doubling the height does not double the speed. It gives about 1.4 times the speed, because speed grows with the square root of height. That is a great pattern to spot.

Link to the game: Mission 1, Downhill dash.

Activity 2: Does the route matter?

Build two ramps from the same height: a steep short one and a long gentle one. Time the marble over the same 1 metre at the bottom.

What to expect: about the same speed. The steep ramp just gets there sooner. In the game, this is what Mission 1 shows.

Ask: Which ramp was faster to the bottom? Which one had the faster marble at the bottom?

Activity 3: Can it climb higher than where it started?

Build a ramp down, then a ramp up on the other side. Try to find a height on the way up that the marble just reaches.

What to expect: it stops a little below the starting height. Mark where it reaches.

Ask: Where did the missing height go? (It turned into heat from friction and into a little sound.)

Link to the game: Mission 2, Up the hill.

Activity 4: The loop

Tape a strip of card or foam into a circle at the end of a ramp, and mark the loop's radius. You want a loop with a smooth entry and exit. Try different start heights.

What to expect: the marble needs a start about 2.7 times the loop radius above the bottom of the loop. In practice, because the marble is not tiny and friction exists, you may need about 3 times.

Ask: What happens if the marble is too slow at the top? (It falls off.) What is the bucket-of-water trick?

Link to the game: Missions 3 and 4.

Extension: different balls

Roll a marble, a hollow plastic ball and a solid rubber ball of the same size down the same ramp. Which wins? A hollow ball is slower, because more of its energy goes into spinning. Mass, surprisingly, does not matter: two solid balls of different weights tie.

Questions that match each mission

Common misconceptions

• "Heavier balls roll faster." On a ramp, all solid balls of the same shape roll at the same speed, whatever their mass.
• "Energy is used up." Energy changes form. When the marble slows, the energy has become heat and sound. It is spread out and hard to use, but it is not gone.
• "Gravity stops the marble at the top of the loop." At the top, gravity is working with the marble's speed to keep it moving along the curve. The danger is that it will fall away from the track if it's too slow.