Simple Machines and Work

Amy Johnson

Simple MachinesStrand 2 – Properties and Principles of

Force and Motion Objective 2 – Forces effect motion

Concept F – Simple Machines (levers, inclined planes, wheels and axles, pulleys) affect the forces applied to an object and/or direction of movement as work is done

GLE

Lesson Overview

SMART Ideas Project

Types of Machines

Machine types

Simple vs. Compound Machine that only

uses one movement Screwdriver =

turning Makes work easier,

faster, and changes the direction of the force or effort

Uses two or more simple machines

Can Opener = wedge + wheel and axle

Makes work easier, faster, and changes the direction of the force or effort

WorkForce causes an object to move in the

same direction as the force that is applied

The greater the force, the more work that is done

Work (in joules) = force X distance (W=fd)

Circle which involves more work? Lifting a shoe or books to your waist

Practice

•Are both people doing work?

•Which picture is showing an example of work?

•Explain how work is being done in one picture but not the other.

ANSWER

Practice If an lifted an object weighing 20 N through a

distance of 0.5 meters, how much work is being done?

If a 60 newton man lifted his 10 newton suitcase a distance of 0.5 meters and ran 25 meters, how much work is being done by the man’s arms and by the man’s legs?

ANSWER

Machines affect workChange size of force you applyChange direction of force Increases mechanical advantage

Mechanical Advantage (MA) The number of times

the applied force is increased by a machine

To figure the MA, you must know the input force and output force Input force is the force

you apply Output force is the force

exerted by the machine

MA = force out (N) force in (N)

FRICTIONThe force that resists sliding motion

between two touching surfaces Ideally, the amount of work you do on

the machine should equal the amount of work done by the machine.

Unfortunately, friction changes some of the input work into heat, therefore, the work out is always less than the work in.

MAP AssesmentA baseball player swings his bat and

hits the baseball with a force of 8 newtons. How much force does the ball exert on the

bat? Describe two forces acting on the ball as it

is flying through the air. 1. 2.

MAP Scoring8 newtons/8 N friction AND gravity

Air resistance is acceptable as friction.

WHOSE DOING WORK?No. The man lifting the grocery bag is

showing work.The direction of the applied force and

motion must be the same. The man carrying the bag is only showing motion, where as the other is applying an upward force to lift the bag up.

Back to question

HOW MUCH WORK? 20 N X .5m =

10 joules of work

man’s arms 10 N X .5m =

5 joules of work

man’s legs 60 N X 25m =

1500 joules of work

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