torque activity by wanghonghx

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									Name:___________________              Torque Activity                Period:____ Date:____

Objective:     Apply the principles of torque and equilibrium to a lever system.

Materials:     meterstick            knife edge             paper clips or string loops as weight hangers
               Hooked masses         unknown mass           balance

Background: A see saw is a simple mechanical device that rotates about a pivot, or fulcrum. Although
            the work output can never be more than the energy input, levers make it easier to
            accomplish a variety of tasks.

Procedure:     Part I
               1. Carefully balance a meter stick horizontally on a knife edge.
               It doesn’t have to balance perfectly, but neither end should be
               hitting the desktop. See diagram at right.

               2. Suspend a 200 g mass 10 cm from the fulcrum. Slide a
               paper clip or loop of string along the meterstick. Hang the
               weight from here. Simultaneously suspend a 100 g mass on the
               opposite side of the fulcrum at a point that balances the
               meterstick. Again, it doesn’t have to balance perfectly, but make it close.

               3. Record the masses and distances in the table.

               4. Make 4 more trials to fill in the table. Change both the distances and the masses. Be
               sure to have different masses on each side of the fulcrum too.

                           Mass #1            Distance from            Mass #2               Distance from
       Trial                (g)               fulcrum (cm)              (g)                  fulcrum (cm)

        1

        2

        3

        4

        5
Part II
5. Remove the masses to leave the balanced
meterstick. Place an object of unknown
mass on one side of the meterstick. At the
same time, on the other side of the
meterstick have a known mass at a position
that balances the system. See figure at right.

6. Record the known mass and distances from the fulcrum for both masses in the
following table.


         Known        Known mass          Unknown        Unknown mass
          mass        distance from       mass (g)        distance from
           (g)        fulcrum (cm)                        fulcrum (cm)
                                             ???


7. Remove the unknown mass, place it on a balance and record its actual mass:_______g




Part III
8. Place the fulcrum exactly at the
85 cm mark of the meterstick.
Balance the meterstick by using a
single known mass that you hang
somewhere on the short end of the
meterstick. See figure at right.

9. Record the known mass and its distance from the fulcrum.

                           Known         Known mass
                           mass (g)      distance from
                                         fulcrum (cm)



10. The mass of the meterstick itself is balancing the known mass. Consider the entire
meterstick to be located at its center of gravity, right at the 50 cm mark.

11. Remove the meterstick, take off the knife edge, place the meterstick on the balance
and record its actual mass:_________ g.
Questions:   1. Use any method you can to discover a pattern to the data table in part I. You could try
             forming ratios or products. You may have already even learned the pattern in class.
             Describe this pattern in the form of a word statement:




             2. Describe the pattern from your data table in part I as a mathematical equation. Use
             appropriate variables or symbols.




             3. Using your equation from above, calculate the unknown mass from part II. Show your
             equation, work, units, etc.




             4. Generally speaking, how does this value compare to the value you obtained with the
             balance?



             5. Using this same equation that you determined, calculate the mass of the meterstick from
             your measurements in part III. Show your equation, work, units, etc.




             6. Quantitatively describe how your calculated value and balance reading compare:

                               calculated value balance reading
                  % error                                                   100%
                                          balance reading

             7. Suppose you are playing see saw with your younger sister who weighs much less than
             you. What two things can you do to balance the see saw?

								
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