Simple Machines

Guilford County Sci VisV205.07

Simple Machines Devices such as

levers, ramps, and pulleys that make our work easier. 

They allow us to apply effort at one place to do work at another point and/or to change the direction of a force.   

One way is to magnify an effort force so that a smaller effort can be applied over a longer distance thus moving a large load a small distance.

Examples: a crowbar being used to

dislodge a boulder, a nutcracker being used

to crack a nut,  or a block tackle pulley

system being used to lift a large weight.  Source:http://www.lakelandschools.org/EDTECH/Machines/RubeMain.jpg

Simple Machines

The mechanical advantage of a machine is the ratio of the load force to the effort force. 

The crowbar, nutcracker, and block and tackle pulley system have a mechanical advantage greater than one. 

Other machines have a mechanical advantage less than one allowing magnification of the distance and speed of a movement. 

An example of this might be a fishing rod or baseball bat. 

Simple Machines

Inclined plane -- a sloping surface, such as a ramp. An inclined plane can be

used to alter the effort and distance involved in doing work, such as lifting loads.

The trade-off is that an object must be moved a longer distance than if it was lifted straight up, but less force is needed.

Examples: staircase, ramp, and bottom of a bath tub

Source: http://www.sirinet.net/~jgjohnso/inclineplanecolored.jpg

Simple Machines

Wedge -- two inclined planes joined back to back. Wedges are used to

split things. Examples:

AxeZipperKnife

Simple Machines

Screw -- an inclined plane wrapped around a shaft or cylinder. This inclined plane allows the

screw to move itself or to move an object or material surrounding it when rotated.

Examples:BoltSpiral staircasewood screwCorkscrewscrews on light bulbs

Simple Machines

Wheel and axle -- a wheel and axle has a larger wheel (or wheels) connected by a smaller cylinder (axle) and is fastened to the wheel so that they turn together. When the axle is turned, the wheel moves a

greater distance than the axle, but less force is needed to move it.

The axle moves a shorter distance, but it takes greater force to move it.

Examples:Door knobWagonToy carBicycle gearsScrew driver

Simple Machines

Pulley -- a wheel that usually has a groove around the outside edge. This groove is for a rope or belt to

move around the pulley. Pulling down on the rope can lift an

object attached to the rope. Work is made easier since pulling

down is assisted by gravity. Examples:

Flag poleCraneElevatorsWindow blinds

Source: http://www.edinformatics.com/math_science/simple_machines/pulley.htm

Simple Machines

Lever -- a straight rod or board that pivots on a point known as a fulcrum. The fulcrum can be moved depending

on the weight of the object to be lifted or the force you wish to exert.

Pushing down on one end of a lever results in the upward motion of the opposite end of the fulcrum.

Examples:Door on hingesSeesawHammerBottle opener

Simple Machines

Classes of Levers The class of a lever is

based on the relative position of the load, effort, and fulcrum.

Levers are classified into 1st class, 2nd class and 3rd class levers.

Classes of Levers 1st class:

Crowbar Scissors

Classes of Levers 2nd class:

Nutcracker Wheelbarrow Doors

Classes of Levers 3rd class:

Tennis racket Tweezers

Questions about Simple Machines What is a simple machine? What are the 6 simple

machines? How does each simple

machine work? How does each machine make

work easier? What are the classes of levers

and how do they work? What is mechanical

advantage?