Simple Machines and Work

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Simple Machines and Work

• Amy Johnson

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Simple Machines

• Strand 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

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Lesson Overview
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Types of Machines
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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

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Work

• Force 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 (Wfd)
• Circle which involves more work?
• Lifting a shoe or books to your waist

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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
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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 mans arms and by
  the mans legs?

ANSWER
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Machines affect work

• Change size of force you apply
• Change direction of force
• Increases mechanical advantage

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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)

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FRICTION

• The 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.

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MAP Assesment

• A 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.

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MAP Scoring

• 8 newtons/8 N
• friction AND gravity
• Air resistance is acceptable as friction.

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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.

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HOW MUCH WORK?

• 20 N X .5m
• 10 joules of work

• mans arms
• 10 N X .5m
• 5 joules of work
• mans legs
• 60 N X 25m
• 1500 joules of work

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