SIMPLE MACHINES

Energy: Ability to do work

Work= Force x Distance

Force: A Push or a Pull

Definitions:

OBJECTIVE 1:I CAN DESCRIBE THE 6 SIMPLE MACHINES

Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.

SIMPLE MACHINES

A simple machine is a device that helps make work easier to perform by accomplishing one or more of the following functions:

• transferring a force from one place to another, • changing the direction of a force, • increasing the magnitude of a force, or • increasing the distance or speed of a force.

SIMPLE MACHINES

The six simple machines are:• Lever • Wheel and Axle • Pulley • Inclined Plane • Wedge • Screw

THE LEVER•A lever is a rigid bar that rotates around a fixed point called the fulcrum.

•The bar may be either straight or curved.

• In use, a lever has both an effort (or applied) force and a load(resistant force).

• the “effort” force moves; not the “resistance” force

Load

Fulcrum

EXAMPLES OF LEVERS

WHEEL AND AXLE•The wheel and axle is a simple machine consisting of a large wheel rigidly secured to a smaller wheelor shaft, called an axle.

•When either the wheel or axle turns, the other part also turns. One full revolution of either part causes one full revolution of the other part.• Examples:

•Car, Wheelbarrow, Motorcycle

EXAMPLES OF WHEEL & AXLE

PULLEY• A pulley consists of a grooved wheel

that turns freely in a frame called a block.

• A pulley can be used to simply change the direction of a force or to gain a mechanical advantage, depending on how the pulley is arranged.

• A pulley is said to be a fixed pulley if it does not rise or fall with the load being moved. • A fixed pulley changes the direction

of a force; however, it does notcreate a mechanical advantage.

• A moveable pulley rises and falls with the load that is being moved. A singlemoveable pulley creates a mechanical advantage; however, it does notchange the direction of a force.

EXAMPLES OF PULLEYS

INCLINED PLANEAn inclined plane is an even sloping surface (higher on one end)

•The inclined plane makes it easier to move a weight from a lower to higher elevation.

EXAMPLES OF INCLINDED PLANES

WEDGE

The wedge is a modificationof the inclined plane. • Wedges are used as eitherseparating or holding devices.

EXAMPLES OF WEDGES

SCREWThe screw is also a modified version of the inclined plane.

•Threads of the screw are like a type of circular ramp (or inclined plane).

EXAMPLES OF SCREWS

OBJECTIVE 2: I CAN EXPLAIN MECHANICAL ADVANTAGE OF A SIMPLE MACHINE

Mechanical advantage

•how many times more force you get out of a simple machine

•Simple machines increase the mechanical advantage

MECHANICAL ADVANTAGE

• A mechanical advantage of 6 means the machine outputs 6 times more force

10 N inMachine

w/

6 M.A.60 N out

OBJECTIVE 3I CAN EXPLAIN THE EFFICIENCY OF A MACHINE

• the input force times the distance equals the output force times the distance, or:

Input Force x Distance = Output Force x Distance

However, some output force is lost due to friction.

•The comparison of work input to work output is called efficiency.

• **No machine has 100 percent efficiency due to friction**

OBJECTIVE 4: I CAN DESCRIBE WORK AND IDENTIFY IF WORK IS BEING DONE

Work is done when a force acts on an object and moves it a certain distance.

• Work = net force x distance (W=Fd)

• The unit for work is the Joule (N·m)

d =

2.5

m

500 N of force

applied

1. How much work is being done by a weightlifter below that applies 500 Newtons of force lifting a mass 2.5 meters?1. F= 500 N d = 2.5 m

2. W=Fd

3. W= (500)(2.5) = 1250 J

d =

2.5

m

500 N of force

applied

2. How much work is being done by a weightlifter below that applies 1000 Newtons of force but does not move the mass?

• F= 1000 N d = 0 m

• W=Fd

• W= (1000)(0) = 0 J

WORK•W=Fd

•No work is done if the object does not travel a distance

WORK OR NOT?•According to the scientific definition, what is work and what is not?•a teacher lecturing to her class•a mouse pushing a piece of cheese with its nose across the floor

26

WHAT’S WORK?

•A scientist delivers a speech to an audience of his peers.

•A body builder lifts 350 pounds above his head.

•A mother carries her baby from room to room.

•A father pushes a baby in a carriage.

•A woman carries a 20 kg grocery bag to her car?

WHAT’S WORK?

•A scientist delivers a speech to an audience of his peers. No

•A body builder lifts 350 pounds above his head. Yes

•A mother carries her baby from room to room. No

•A father pushes a baby in a carriage. Yes

•A woman carries a 20 km grocery bag to her car? No