Design and create a gear

Gather all materials on a clear table so you can work without losing anything.

Place a cup or use a compass to draw two different-sized circles on the cardboard for two gears.

Cut out the two cardboard circles carefully with scissors or a craft knife.

Find and mark the center of each circle by drawing two straight lines across and marking their crossing point.

Pick how many teeth each gear will have and write that number on each circle.

Wrap the piece of string once around a circle and mark where the string meets to measure its circumference.

Measure the marked string length with the ruler and divide that number by the tooth count to get one tooth spacing.

Fold or mark the string into equal segments using the tooth spacing measurement so each fold is one tooth wide.

Lay the folded string around the circle and make small pencil marks at each fold to mark every tooth position.

Cut small triangular teeth at each pencil mark around the edge of each circle.

Make a hole at each circle’s center slightly wider than your straw or skewer and push the straw or skewer through to make an axle; secure with tape or a brad.

Put the two gears on their axles with their teeth touching and turn one gear to watch the other move and notice how direction and speed change.

Try different-sized gear pairs and count how many turns the small gear makes while the big gear makes one turn to see the speed change, then share your finished creation on DIY.org