GEARS

Gears Are toothed wheels

Transmit a rotational force to another gear or device

Teeth mesh with another gear to stop slipping

Gears as simple machines: Gears can be combined with gears of

different diameters to produce a MECHANICAL ADVANTAGE

As the rotational speed & torque of the second gear are different from the first gear.

Rotational Speed

The larger the radius of a gear the slower its rotational speed.

The speed ratio, known as the gear ratio, can be calculated from the number of teeth

Gears can increase speedIf the driving gear has more teeth than the driven gear it will make it turn faster (but with less force).

Torque Larger gears have

greater torque than smaller gears

Remember: Torque is a force that tends to rotate or turn things. 

Gears can increase power

If the driving gear has less teeth than the driven gear it will make it turn with more force (but slower).

Gears on Bicycles

Chain wheels (Driver)

Freewheel(spins free in one direction and locks in the other)

What do gears on a bike do? Gear allow the rider to change the

number of times the rear wheel rotates for each pedal rotation

This affects the distance the bicycle travels with each pedal rotation

Gears also allow the rider to change the force with which the rear wheel turns

Calculating Gear RatiosCalculated by dividing the number of teeth on the driving gear by the number of teeth on the driven gear.

Example:Driving gear has 25 teethDriven gear has 75 teeth

Your Turn:Calculate the gear ratio for bicycle with a front chain with 22 teeth and rear gear of 30.

HINT: You may want to use a calculator

Answer:Calculate the gear ratio for bicycle with a front chain with 22 teeth and rear gear of 30.

2230=0.73: 1

Biscuit Factory: Gearshttp://simon.sjc.vic.edu.au/TLFLearningObjects/DVD/los/L2375/index.html