Lesson  Nine

Pulley

                                     Work smarter, not harder.
 
 

   Objectives :  Students will be able to:

   Time and Materials    Lesson:

          Has anyone seen a flagpole with a flag on it?  Does it stay up there all the time?  How does it get to the top?  Today we're going to talk about the simple machine that helps raise the flag.   Write the word pulley on the chalkboard.
 

           Hold up the pulley.  This is a pulley, it is a wheel with a groove on each edge to hold a rope or a chain.  Pulleys are used to lift things.  Today we're going to see how the pulley helps lift this bucket of rocks.  Set broomstick across the backs of the two chairs.  Attach the spring scale to the bucket and have a student lift it.  Record the measurement on  the  board.  Now let's  measure the force used when a fixed pulley is used to lift the load.  Attach the pulley to the bucket and have a student pull on the spring scale attached to the cord to raise the bucket.  Record on the board the measurement shown.  Which took less force, using our arms to lift the load or using the fixed pulley to lift the load?  The fixed pulley doesn't require less force to lift the load but it changes the direction of the force.  If we didn't have a pulley to help us, the custiodian would have to climb the pole to put up the flag.
           A different type of pulley is the moveable pulley.  It is attached to the load and moves with it.  Let's try our bucket experiment with a moveable pulley.  Tie the  pulley cord to the broomstick over the chairs.  Attach the moveable pulley to the bucket and place it on the cord.  Hook the spring scale  to the end of the cord and have a student hold the spring scale to raise the bucket.  What measurement  does the spring scale show?  It should measure 1/2 of the force used with a fixed pulley.  Do we use less force with a fixed or moveable pulley?  Write on board a moveable pulley uses less force to lift a load.
 


          Review the experiment with the students and give them the opportunity to write in their Science Journal, using the steps of the scientific procedure.

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