Unit 4 Mechanical Systems Topic 2 Wheel and Axle, Gears, and Pulleys Remember to name and date your notes!

Wheel and Axle The wheel and axle is a large wheel and a smaller wheel mounted on a common axis so that the wheels rotate together. Wheel – larger Axle - smaller

A wheel and axle can provide a mechanical advantage – remember that this means that you will receive more effort from the machine than the amount of effort you put into it. Eg. Door knob, steering wheel

In order to get this mechanical advantage, your effort must be applied to the wheel. (remember, this is the bigger one)

A wheel and axle can also provide a speed advantage. Riding a tricycle would be a good example. You apply your effort to the axle (pedals), which is connected to the wheel, and you gain speed. You must put out a large effort force.

Gear A gear wheel is a wheel with identical teeth arranged around its edge. It is used to transfer force to another gear wheel. A gear train consists of two or more gear wheels that mesh so that rotary motion and force can be transferred to another gear.

The larger gear in a gear train is called the gear wheel. The smaller gear in a gear train is called the gear pinion.

Driving gear (driver) – turns due to motor, human, etc. Driven gear (follower) – turns because it is attached to the driving gear.

Multiplying gears consist of a large driving gear with a small driven gear that combine to provide an increase in rotational speed. Reducing gears consist of a small driving gear with a large driven gear to provide a decrease in rotational speed.

Can gears turn without touching each other? Think about a bike. The two (or more) gears are attached by a chain. These gears are called sprockets.

The effort force is on the front sprocket. The rear sprocket is the driven gear.

DON’T WRITE If the front sprocket on a bike has 45 teeth, and the back sprocket has 15 teeth, how many times will the back sprocket turn with one turn of the front sprocket? ANSWER 

3 You just solved what is called a speed ratio. This is the relationship between the speed of rotations of a smaller gear and a larger gear.

Speed ratio = # of driver gear teeth # of driven gear teeth

PULLEY A grooved wheel with a rope or chain running along the groove.

Fixed pulley – does not move and is attached to something like a ceiling. It simply changes direction of the effort force. Moveable pulley – often attached to a rope…the rope is then fixed to the ceiling.

The more pulleys you use, the greater the mechanical advantage will be that you will gain.

To calculate the MA of a pulley system, count the number of rope segments, but do not count the rope being pulled down.

Don’t count 1 3 4 2

Pulleys are used to: reduce the effort force needed to lift a load or to allow the lifting of a load by pulling down rather than lifting up.