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Experiments

Kitchen-table experiments

Six quick experiments with things from the kitchen drawer. Nothing sharp, nothing hot.

Before you start. Have a grown-up nearby, clear a space on the table, and keep heavy things low down. Every experiment here uses everyday things: rulers, coins, books, string and rubber bands. The “why” under each one is linked to its source.

Jump to: Ruler seesaw | Three levers | Rubber-band ramp | Paper screw | Pencil winder | Broom pulley | Butter-knife wedge

1. The ruler seesaw (lever)

You need: a 30 cm ruler, a round pencil, a handful of the same coins.

  1. Lay the pencil on the table and balance the ruler across it at the 15 cm mark.
  2. Stack 4 coins at one end. How many coins at the other end balance them?
  3. Now move the pencil so it sits 10 cm from the 4-coin end. Try again.
  4. Move it closer still. Write down coins and distances each time.

What happens. The closer the pencil (the fulcrum) is to the stack, the fewer coins you need at the far end. Twice as far out needs about half as many coins.

Why. The law of the lever: weights balance at distances from the fulcrum in inverse proportion to their weights. Twice the weight balances at half the distance. Britannica The closer the fulcrum is to the object being lifted, the easier it is to lift. Science Trek

2. Three levers with one ruler

You need: the same ruler, pencil and coins, plus an eraser.

  1. First class: pencil in the middle, coins at one end, press the other end.
  2. Second class: pencil under one end, coins in the middle, lift the free end with one finger.
  3. Third class: pencil under one end, coins at the far end, lift the ruler from the middle.
  4. Which felt easiest? Which made the coins move furthest?

What happens. Second class feels easiest. Third class feels hardest, but the coins move further than your finger does.

Why. In a first-class lever the fulcrum is between the effort and the load, as in a seesaw or a crowbar. BBC Bitesize In a second-class lever the load is between the fulcrum and the effort: wheelbarrows, nutcrackers and some bottle openers. BBC Bitesize In a third-class lever the effort is between the fulcrum and the load: tweezers, tongs and fishing rods. BBC Bitesize

3. The rubber-band ramp (inclined plane)

You need: a small heavy book or a full tin, a long rubber band, a tray or chopping board, a pile of books, a ruler.

  1. Hook the rubber band round the tin (or tie it on with string) and lift it straight up by the band. Measure how long the band stretches.
  2. Make a ramp with the tray leaning on the pile of books.
  3. Pull the tin slowly up the ramp by the band. Measure the stretch again.
  4. Add books to make the ramp steeper, and measure again.

What happens. The band stretches less on the ramp, and more as the ramp gets steeper. You pull for longer, though.

Why. Pushing something up a slope takes less force than lifting it straight up, if you ignore friction. Britannica The steeper the slope, the closer the force gets to the full weight. Britannica It takes the same amount of work, but less force, to move an object up a ramp than to lift it straight up. Science Trek

4. The paper screw (screw)

You need: a sheet of paper, a pencil, a felt-tip pen, a ruler, child-friendly scissors.

  1. Draw a right-angled triangle on the paper, about 20 cm along the bottom and 10 cm up the side, and cut it out.
  2. Colour along the long sloping edge with the felt tip.
  3. Lay the pencil on the tall side and roll the paper round it.

What happens. The coloured edge spirals round the pencil like the thread of a screw.

Why. Cut a right-angled triangle of paper and wind it round a pencil: the sloping edge becomes a screw thread, an inclined plane wrapped round a cylinder. US Navy In terms of how it works, a screw may be thought of as a wedge wrapped around a cylinder. Britannica

5. The pencil winder (wheel and axle)

You need: a pencil, a cotton reel or a lid with a hole, sticky tape, string, a small bag of coins.

  1. Tape the string to the middle of the pencil, tie the coin bag to the other end, and wind it up by twisting the pencil with your fingertips.
  2. Now push the pencil through the cotton reel (or tape a big round lid to it) and wind by turning the reel instead.

What happens. Turning the wide reel is easier than twisting the thin pencil, but you turn it further for the same lift.

Why. Its mechanical advantage is the radius of the wheel divided by the radius of the axle. Britannica In its earliest form, the wheel and axle was probably used for raising weights or buckets of water from wells. Britannica

6. The broom-handle pulley (pulley)

You need: two broom handles, a long rope or washing line, three people.

  1. Two people stand a metre apart, each holding a broom handle.
  2. Tie the rope to one handle, then loop it round both handles three or four times.
  3. The third person pulls the loose end gently while the others try to hold the handles apart.

What happens. The single puller wins: every extra loop adds another rope section, and makes the pull easier but longer.

Why. For a pulley system, the mechanical advantage is roughly the number of rope sections holding up the load: 2, 3, 4 and so on. OpenStax Machines multiply force at the expense of distance: you push with less force, but over a longer distance. OpenStax

Bonus: the butter-knife wedge (wedge)

You need: a lump of play dough, a blunt butter knife.

  1. Press the flat back of the knife into the dough.
  2. Now press the thin edge in, with the same push.

What happens. The thin edge sinks in and pushes the dough apart to the sides; the flat back hardly moves.

Why. A wedge tapers to a thin edge. Push it one way and it pushes sideways. Britannica A wedge is really two inclined planes back to back. Science Trek

These are classroom-style activities written for this site, based on the sourced principles under each one. Results vary with friction, so do each test two or three times.