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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