Simple Machines and Work
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Transcript of Simple Machines and Work
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
Back to question