Experiments

Steam science without the steam

No kettles, no flames. Everything here runs on muscles, breath and a bit of maths. (Real steam is properly hot, which is why we leave it to the museums.)

1. The syringe squeeze

1. Take a plastic syringe with no needle and pull the plunger halfway out.
2. Put your finger firmly over the end.
3. Push the plunger in. Feel it push back?
4. Let go of the plunger and watch what it does.

In the mid-1600s Robert Boyle studied how the pressure and volume of a trapped gas are linked. NASA Glenn Research Center: Boyle’s law Boyle found that pressure times volume stays nearly constant: halve the space and the pressure goes up to match. NASA Glenn Research Center: Boyle’s law

NASA’s worked example: a gas filling 4.0 cubic metres at 1.0 kilopascal shrinks to 3.0 cubic metres when the pressure rises to 1.33 kilopascals. NASA Glenn Research Center: Boyle’s law

2. The card crank

1. Cut a circle of card and push a pencil through the middle for an axle.
2. Make a hole near the edge and loosely fix one end of a paper strip there with a split pin.
3. Slide the other end of the strip back and forth in a straight line.
4. Watch the circle go round. That’s a crank.

In the classic engine the piston rod drives a crank on a flywheel, which turns the back-and-forth push into round-and-round motion. Encyclopaedia Britannica: steam engine

3. The flywheel test

1. Make two card circles the same size, each with a pencil axle.
2. Tape coins round the edge of one.
3. Give each the same flick and time how long it spins.
4. Which keeps going longer? Write it down.

A flywheel’s inertia resists changes in speed, smoothing out the jerky pushes of the piston. Encyclopaedia Britannica: flywheel Spin a flywheel twice as fast and it stores four times the energy. Encyclopaedia Britannica: flywheel

4. The balloon spinner

1. Tape a bendy straw into the neck of a balloon, bent sideways.
2. Push a pin through the top of the balloon into a pencil rubber, so it can turn.
3. Blow it up through the straw, then let go.
4. Air rushes out sideways and the balloon spins, a breath-powered cousin of Hero’s steam ball.

The aeolipile is a ball on a boiler with two angled nozzles: steam squirts out and the ball spins. Encyclopaedia Britannica: Heron of Alexandria

In a steam turbine, the steam rushes out of nozzles at high speed and spins the blades directly, with no piston at all. Encyclopaedia Britannica: steam engine

5. How many horsepower are you?

1. Measure the height of a flight of stairs in feet.
2. Time yourself walking (not racing) up it.
3. Pop your weight in pounds, the height and the time into the calculator.

Physicists define work as force times the distance something moves. NASA Glenn Research Center: work Power is how fast work gets done: the rate of change of work over time. NASA Glenn Research Center: work

One horsepower is 33,000 foot-pounds of work a minute. Encyclopaedia Britannica: horsepower One horsepower is about 746 watts. Encyclopaedia Britannica: horsepower

The steps are our own wording; the facts beside them link to their sources. Ask a grown-up before borrowing coins, balloons or the stairs.

Next: the steam timeline →