Real Work:

The Great Pyramid

Built 2600 B.C. - requiring massive resources.

Estimated to have 2,300,000 stone blocks weighing from 2 – 30 tons and some weighing 70 tons.

The Great Pyramid

To finish in less than thirty years, the Egyptians would have had to cut, move, and lift about 200 blocks per day!

The mortar used is of an unknown origin. It has been chemically analyzed, but cannot be reproduced.

Great Pyramid

Known Machines used by the Egyptians:

Incline ramps { decrease effort },

wood logs { wheels }, and

large crowbars {lifting and moving}.

Welcome to a world full of machines!

There are machines all around us!

A machine is a device with moving parts that work together to accomplish a task.

Example: A bicycle transforms forces from your muscles into speed and motion.

Why do we need simple machines?

Work means that we are exerting force and moving something.

The 6 simple machines make our work easier. We expend less energy (force) by using simple machines.

Machines

The INPUT includes everything you do to make the machine work.

The output is what the machine does for you, such as going fast.

6 Simple Machines

All machines are made up of some of the

6 simple machines.

Levers Inclined Planes

Wedges Screws

Wheel and axle Pulley

The 6 Simple Machines

Lever Pulley

Wheel and Axle

WedgeScrew

Inclined Plane

Levers

There are three parts to a lever:

Load Force Fulcrum: support or

balance

Classes:

Levers help us

to do work more

effectively.

Levers

Mechanical Advantage

MA = Output Force (N) / Input Force (N) 1 Newton (N) = 0.228 pounds 1 Pound = 4.48 Newton’s (N)

Mechanical Advantage

Mechanical Advantages

Using levers

properly provides

Large

Mechanical

Advantages

Incline Plane (Ramp)

It is a slanted surface

It makes moving objects easier.

The longer the ramp – compared to its height the greater the MA.

Wedges

Wedges that split:

Your teeth! Every time you bite into something, you are using a wedge.

Wedges that cut:

A saw! A knife!

Wedges

Wedges that tighten:

A doorstop to keep the door open.

Wedges that hold things together:

A nail holds wood to a wall or other wood.

The longer and thinner the greater MA.

Wedges

A wedge is used to split, tighten, or secure a hold.

A wedge is usually a triangle shape with a sharp point.

If you apply force at one end, the wedge will go between something, in this case an ax splits a piece of wood.

Screw

The three parts to a screw: Head - Shaft - Tip The head is the part that you exert a force on. The shaft has ridges, called

threads that wind around the screw. As the screw is rotated it exerts a small force over a great distance.

The tip is sharp.

How to use a screw:

Fasten two things togetherWhen you turn it clockwise, the threads

cut a groove down and into the material, making a hole. The threads holds the screw tightly in place.

To remove the screw you turn it counterclockwise, thus the screw pushes up and out of the material.

The Wheel and Axle

Two or more wheels are connected by an axle.

The wheel turns with or around the axle.

This car wheel has a big axle that it rotates around when the car moves.

Why do we need wheels?

Wheels help us move heavy objects. They roll easily.Did you know a doorknob is really two

wheels connected by an axle? You can’t see the axle because it’s inside the door, but it’s there!

If there wasn’t an axle, the doorknob wouldn’t turn!

Another type of wheel: Gear!

A gear is a wheel with teeth. The teeth fit in between each other and

turn. When one gear turns, its teeth push

against the teeth of the other gear and they both turn.

There are gears on your bike, on a can opener and on an egg beater.

Gears

If one gear has 36 teeth and the other has 12 teeth, then the smaller one would have to turn three times for the larger (36 teeth) gear to rotate once.

3 X 12 = 36

Pulleys

Lifting a bucket full of water is a lot of work!

A pulley is a wheel with a rope running over it. The wheel has a groove, called a sheave, and it keeps the rope from slipping off the wheel.

Remember, since there is a wheel in a pulley there also has to be an axle!

Block & Tackle

The Block and Tackle

is another simple

machine that uses

ropes and pulleys to

multiply forces.

Block & Tackle

Mechanical

Advantage = 2

Output / Input = MA

10 (N) / 5 (N) = 2

Block & Tackle

Note the number

of ropes yielding

greater output

capacity, thus

a larger MA.

Problem

Suppose a

Woman raises

a 65 N object

1.6 m in 4 s.

The work done

and her power

can be

Calculated:

W = F x D

65 N x 1.6m = 104J

P= W / T

104J / 4 s = 26 W