CHANGING GEAR

Gears in the car help transfer movement in the most efficient way. They do this by transmitting movement from the crankshaft to another shaft called the propeller shaft. The propeller shaft rotates more slowly than the crankshaft and adapts the movement, so that the car can cope better with different speeds and efforts, such as starting and going uphill. The change in speed of rotation between the two shafts is controlled from the car's gearbox. As a driver changes gear, toothed wheels that are connected to the crankshaft engage with other toothed wheels joined to the propeller shaft. The difference in the number of teeth on each wheel determines the number of times the wheels turn, as the first project demonstrates. The second experiment shows how gear wheels work in a car. The larger corrugated card wheel has more teeth than the two smaller wheels.

DRAWING THE GEARS

YOU WILL NEED

• Compass,
• ruler, pencil,
• 8 1/2 x 11in sheet of white paper,
• black pen, scissors,
• 8 1/2 x 11in sheet of thin card,
• two strips of corrugated card,
• tape,
• three colored felt-tipped pens.

STEP 1
Using the compass, trace a 5 1/2 in diameter circle on the paper. Draw over it with the pen and cut it out. On the card, trace draw, and cut out an 4 1/4 in diameter circle.

STEP 2
Tape corrugated card around the circles. Make a hole in the small circle wide enough for the tip of a felt-tipped pen. Turn the small wheel inside the larger. Trace the path in felt-tipped pen.

STEP 3
Make a second hole in the small wheel. Turn the small gear inside the larger using another felt-tipped pen. Make a third hole in the small wheel and use a third color pen.

THREE-GEAR MACHINE

YOU WILL NEED

• Compass,
• ruler,
• pencil,
• 8 1/2 x 11in sheet of card,
• pen,
• scissors,
• three strips of corrugated card,
• tape,
• 8 1/2 x 11in piece of fiberboard,
• white glue,
• 2 1/2 in piece of 5/8in diameter wood dowel,
• three map pins.

STEP 1
Use the compass to trace one 5 1/2 in diameter and two 4 1/4 in diameter circles on the card. Draw around the circle edges with the pen, and cut the circles out.

STEP 2
Carefully wrap the strips of corrugated card around the circles, using one strip per circle, corrugated side out. Tape each strip to the bottom of the circles.

STEP 3
Place the largest gear wheel on the piece of fiberboard. Hold the gear down and glue the dowel on to the side of the gear base at the edge of the wheel. Leave it until it is dry.

STEP 4
Position all three gears on the fiberboard, with the edges just touching each other. Pin each of them firmly to the fiberboard with a map pin, but allow them to turn.

STEP 5
Gently turn the dowel on the largest gear. As that gear turns, the two others that are linked together by the corrugated card will turn against it.