Simple Machines and Work Amy Johnson

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 GLE

Lesson Overview

Types of Machines

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

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 (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 work  Change size of force you apply  Change 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)

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.

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.

MAP Scoring  8 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