Unit 3.2

What is a Machine?

What is a Machine?

Machine – a device that allows you to do work in a

way that is EASIER!

There are 3 ways a machine makes work easier:

1. Changes the amount of force you exert (or apply).

2. Changes the distance over which you exert your force.

3. Changes the direction in which you exert your force

Input and Output Force/Work Input Force – the force

that occurs when YOU move the machine a certain distance

Output Force – the force that occurs when the MACHINE moves an object a certain distance.

Input Work – the input force multiplied by the distance

Output Work – the output force multiplied by the distance

Input and Output Force/Work Changing Force :

The input force is less

than the output force

on a faucet.

Changing Distance:

The input distance is

shorter than the output

distance.

Changing Direction:

The machine changes

the direction of your

force. This makes it

easier for you.

Mechanical Advantage Mechanical Advantage – the number of times a machine

increases a force exerted on it.

Mechanical Advantage = Output force

Input force

Ex. You exert an input force of 10 Newtons on a hand-held can opener. The opener exerts an output force of 30 Newtons. What’s the mechanical advantage of the can opener?

Mechanical Advantage = Output force = 30 N = 3 (TRIPLES YOUR INPUT)

Input force 10 N

Simple Machines

The six types of simple machines are:

1. the lever

2. the pulley

3. the wheel and axle

4. the inclined plane

5. the wedge

6. the screw

Simple Machine Families

Simple machines are divided into two families: the

lever family and the inclined plane family.

Lever family:

lever

pulley

wheel and axle

Inclined plane family:

• inclined plane

• wedge

• screw

Lever – The Lever Family Lever - a rigid bar that is free to pivot (or rotate)

on a fixed point

Fulcrum – the fixed point in which a lever pivots

around

Ex: hammer, scissors,

see-saws

There are 3 different types or

classes of levers:

Pulley – The Lever Family

Pulley – a simple machine made of a grooved wheel

with a rope or cable wrapped around it.

There are two basic types of pulleys:

Fixed Pulleys – a pulley attached to a structure

Ex: Top of the flagpole that raises or lowers a flag.

Moveable Pulleys – a pulley attached to the object you

want to move

Ex: A zip-line going through a forest

If you put a fixed and moveable pulley together, you get

a block and tackle pulley, such as a construction crane.

Pulley – The Lever Family

Wheel and Axle – The Lever Family Wheel and Axle – a simple machine made of two

cylindrical objects fastened together that rotate about

the same axis.

Ex. Screwdriver,

doorknob, and

car’s steering wheel

Inclined Plane – The Inclined Plane Family

Inclined Plane – a flat,

sloped surface

An inclined plane allows

you to exert your force

over a longer distance

(making your job easier).

Inclined Plane – The Inclined Plane Family

Wedge – The Inclined Plane Family Wedge – a device that is thick at one end and tapers to

a thin edge at the other end.

A wedge is a modified inclined plane. Instead of moving

along an inclined plane, you move the inclined plane

itself. Ex: Axe, zipper, pencil sharpener, cheese grater.

Screw – The Inclined Plane Family

Screw – an inclined plane that is wrapped around a

cylinder. The spiral forms the threads of the screw.

Imagine a road going around a mountain from base to

top. Then turn that mountain upside down with the road

still attached.

Ex: Screws, bolts, light bulbs, jar lids

Graphic Organizer

Wheel and axle

Simple Machine Member of Which Family Example (at least 3)

Inclined plane

Wedge

Screw

Lever

Pulley