Iron Science Teacher

On 28 July 2000

The secret ingredient was aluminum foil.

Paul and Raleigh made an electric fuse

Sue did a catapult

There were also match rockets

I did an exploration of how aluminum foil shapes fell in air and water.

When all the explorations had been shared, the audience chose the Iron Science Teacher.

Paul Doherty

Here is the activity I did with aluminum foil.

Falling with Resistance

Introduction

Drop aluminum foil shapes in air and water. Predict what will happen then observe what does happen and do experiments to figure out your results.

Material

Aluminum foil, It is easiest if you do not use the thinnest aluminum foil.
A fish tank full of water at least 25 cm (10 inches) deep.

Assembly

Cut the aluminum into 9 squares 10 cm (4 inches) on a side.

To Do and Notice/What's Going On?

Two flat foils in air

Fold up the edges of two of the squares.

Bend a 0.5 to 1 cm wide rim up at a 45 degree angle around the all of the edges of two of the squares. (This will allow the squares to fall stably down through the air.)

Hold the two identical squares side by side. Ask friends to predict what will happen when you drop them.

Drop the squares.

They drop together through the air.

A flat foil versus a ball

Now wad up one of the squares into a ball.

Hold it next to the flat piece of foil and ask people what will happen when you drop them both at the same time.

The ball of aluminum foil falls faster than the flat foil. There is more air resistance on the flat foil and so it accelerates downward more slowly than the ball.

The flat foil and ball underwater

Hold the flat foil side by side with the foil ball midway between the top and bottom in the tank of water.

Ask the observers what will happen when you release both at once.

Release the flat foil and the ball.

Notice that the crumpled ball rises to the surface and the flat piece sinks slowly.

People may guess that there is air trapped in the foil when it is crumpled into a ball. The air would make the foil ball less dense than water so that it will float.

Ask if they can conceive of an experiment to test this theory. If they find one, do it.

Here is a simple test of the theory.
Take another piece of aluminum foil and hold it under water, crumple it into a ball.
Ask people what will happen when you release it.
Release it. Notice that this ball sinks.

Hold the underwater-crumpled ball of aluminum foil next to the flat foil. Release them at the same time. Predict what will happen.

This time they both settle to the bottom. The ball falls to the bottom before the flat foil for the same reason as it does in air.

What's Going On?

The aluminum foil is denser than air and water. So flat or ball shaped aluminum will sink in water, unless there is air trapped in the ball. The flat foil has more air resistance than the ball and so the flat foil will fall slower in air, the flat foil has more resistance to moving through water too, so it settles to the bottom more slowly in water.

 Scientific Explorations with Paul Doherty © 2000 1 August 2000