Simple Machines’ Study Guide
A machine is any device that makes work easier.
A complex or compound machine is any machine that uses 2 or more simple
machines.
You will need to be able to list the following six simple machines and give an
example of each.
Machine & Examples
1. Lever: teeter-totter, pliers, crow bar, wheel barrow
2. Wheel and axle: pencil sharpener, wagon wheel
3. Pulley: curtain rod, flag pole, crane
4. Wedge: knife, axe, door wedge
5. Inclined plane: slide, ramp
6. Screw: light bulb, jar lid
Wedges, Screws, and Inclined Planes
Wedges are inclined planes used as tools. Many wedges are two inclined
planes put together. Screws are inclined planes wrapped around a pole.
You will need to be able to label the fulcrum, resistance, and effort on the
levers below.
Work, Force, and Distance
You will need to be able to use this formula:
F x D = W; Force (lbs.) times distance (feet) equals Work (foot-pounds)
Example:
How much work does it take to lift a 30 lb. block of cement 4 feet?
30lbs x 4ft = 120 foot-pounds
Based on the following picture, the output is going to have more speed.
Output
Drive Wheel (Crank)
Based on the following picture, the output is going to have more force.
Output
Drive Wheel (Crank)
Miscellaneous information you need to know:
When using a ramp, if you want to make work easier, you have to increase
the slope of the ramp.
Friction is harmful when it causes things to wear out. Examples would be
when the belt in a car wears out due to rubbing and friction or the soles of
your shoes lose their tread. Friction is helpful when you use the brakes on
your bike to slow you down so you do not crash. Oil is used to reduce
friction.
Gears are better than pulleys when you need something to last a long time
and not have any slippage.
Work only happens when movement occurs.
If you increase the amount of force you need to use, you decrease the
distance. If you increase the amount of distance, you decrease the amount
of work.
A large drive wheel (the wheel that has the crank) attached to a smaller
wheel will give off more speed. A small drive wheel attached to a larger
wheel will give off more force.
A block and tackle will lift an object more easily than a single fixed pulley.
To get the greatest mechanical advantage (easier to use) when using a lever,
place the fulcrum closest to the resistance. See the pictures below for
examples.