Unit #4 Topic #2 Wheel and Axle, Gears and Pulleys

Last topic we discovered that you can lift a heavy load as long as you find a lever strong enough and long enough to do the job Sometimes though, levers are not practical Fortunately, there are many other simple machines that can give you a mechanical advantage great enough to move a heavy load with a much smaller effort force

Wheel and Axle A device with two turning objects attached at their centres where one causes the other to turn is called a wheel and axle. Wheel and axles are pretty much everywhere you look. Can you see some examples right now?

Wheel and Axle A device with two turning objects attached at their centres where one causes the other to turn is called a wheel and axle. Wheel and axles are pretty much everywhere you look. Can you see some examples right now? How about: the faucet, a doorknob Other ex: steering wheel, bicycle, winch

Example of a winch (wheel and axle)

Gears A wheel and axle provides speed for a race car flying around the track However, the wheel and axle are attached to each other so each makes the same number of rotations every second. What if you wanted to make one wheel rotate faster than another?

A gear is a rotating wheel-like object with teeth around its rim A group of two or more gears is called a gear train.

The first gear or driving gear (driver) may turn because someone is turning a handle or because its attached to a motor. The second gear is called the driven gear (follower)

Can one gear turn another gear without touching it?

Can one gear turn another gear without touching it? Think about the gears on your bicycle. A gear with teeth that fit into the links of a chain is called a sprocket.

Don’t get confused with the following sprockets!!!! Toad The Wet Sprocket Sprocket from Fraggle Rock

Speed Ratio Each link of a bicycle chain moves the same distance in the same amount of time If the front sprocket moves the chain a distance of 45 teeth, the back sprocket will also move the chain 45 teeth. However, if the back sprocket only has 15 teeth and the front sprocket has 45, the back sprocket will make three full turns for every one of the front sprocket

The relationship between the speed of rotations of a smaller gear and a larger gear is called speed ratio. Speed Ratio = # of driver gear teeth # of follower gear teeth

Pulleys A pulley is a grooved wheel with a rope or chain running along the groove. A pulley is similar to a Class 1 lever, but instead of a bar, a pulley has a rope. The axle of the pulley acts as the fulcrum and the two sides of the rope act as the effort and load arms

Pulleys can be fixed or moveable. A fixed pulley is attached to something that does not move, such as a ceiling, wall or tree. A moveable pulley is attached to something else, often by a rope that goes around the pulley itself.

If you compare a pulley to a lever, then you will discover that the effort arm and load arm are the same. So how do pulleys help you lift heavy loads? A single pulley may make lifting more convenient, but combinations of pulleys are required to lift heavy loads. A combination of fixed and moveable pulleys is called a block and tackle or a compound pulley.

Next Science Class You will be working in groups on 3 different exploratory activities 1) Turnaround Time 2) Gear Up For Speed 3) Tug of War