Magnetic Pennies

In this activity you will find that some pennies are attracted to magnets, which allows them to do some pretty amazing things.

Year groups: 3-7 (ages 7-12)

Educational objective

To explore the magnetic attraction of a range of different magnets on 1p and 2p coins.

Key student learning

Some 1p and 2p coins are made of steel, which is magnetic.
Some 1p and 2p coins are made of bronze, which is not.
Very strong magnets can attract a 'string' of pennies.
The friction on the bottom penny in a string is very low, so it spins easily with very little resistance.

Materials needed, per student

Assorted 1p and 2p coins
1 rare-earth (e.g. neodymium) magnet
Assorted other magnets
1 drinking straw

Practicalities

Rare-earth magnets are very strong. You can buy them from educational suppliers, e.g. www.mutr.co.uk. Be careful when bringing two rare-earth magnets together in case your skin is trapped between them.
Bar magnets work best for this activity as it is easier to balance your magnetic sculptures on a flat magnet.

Open-ended investigation

For a more inquiry-based activity, encourage the class to respond to a series of challenges. For example, how many pennies can you attract to the magnet? What is the longest string of pennies you can suspend? What is the most unusual shape you can make with the pennies and magnet? Can you make a penny spin without touching it? Can you make a magnet roll uphill without touching it? What magnetic penny tricks can you do? Click here for a guide to planning open-ended investigations in your classroom.

Discussion

What do you notice about the pennies (dates, shininess) that are and are not attracted to the magnet? Can you use what you find out to predict if a penny will be magnetic?

'Copper' (1p and 2p) coins produced after 1992 are made from copper-plated steel (earlier coins were made from bronze). Steel is an alloy of iron and carbon; it's the iron that makes the coins magnetic. Iron, nickel and cobalt are the only magnetic metals.

How can the bottom coin in a chain spin so fast?
The magnetic force from the magnet holds the coins in place, but the effect is weaker on coins that are further away. In a chain the very last coin is barely held in place, and it touches its neighbour at a tiny spot where their rims meet.

This minimal contact, and the smoothness of the rims, means that there's only a small amount of friction acting on the penny when it spins. Friction slows things down. In this case the small amount of friction means that the coin turns quickly and keeps spinning for quite a while.

Extensions

Make a string of pennies then use the straw to blow the bottom penny. See how quickly and easily it spins. Why is that?
Use a metal extending tape measure with a magnet on one side and a coin on the other to roll the magnet uphill or upside down.

Links to everyday life

The Earth is a magnet

The Earth's hot core contains liquid iron which is constantly in motion, creating an electric current which produces a magnetic field. It has a north and south pole, but these magnetic poles aren't quite lined up with the geographic North and South Poles on a map, because the molten inner core's poles are always wandering around. Like other magnets, the Earth attracts things, e.g. the small magnetised needle in a compass.

Aurora borealis

When you mix together electricity, magnetism and gases you get an aurora. Sun storms produce huge flares of electrically charged particles and generate powerful solar winds that blast the Earth's atmosphere. The Earth's magnetic field repels most of this electrical attack, but captures a fraction of it, which leaks down to the atmosphere at the magnetic poles. When the Sun is particularly active, this electrical energy passes through the thin gases in our atmosphere so they glow with coloured light like a fluorescent tube or a plasma ball.