1. Draw a sketch of a hammer removing a nail from a board. Where is the fulcrum? What class lever is it? Why?

2. Draw diagrams of the three classes of levers and give an example of each kind.

3. Name some examples of bent levers.

4. Give three examples of compound levers.

5. Define fulcrum, force arm, and weight arm.

6. Will a mechanic who knows why he performs each operation of his trade enjoy his work better than one who does not? Explain.

Fig. 16. - Bell-Crank Lever. Another type of bent lever.

7. Explain why some hammers are large, some small, and of different shapes.

8. Is it necessary to know the principles of science in designing a tool?

9. What would happen to a mechanic if he used a hammer four times as heavy as necessary? Would he accomplish as much work with the large hammer as the small hammer (assuming the small hammer will do the work effectively)?

10. Why not use a claw hammer in driving tacks into the floor?

11. Name a number of "hitting tools." Notice the manner in which they are used. Is it practically the same? What is the mechanical principle involved?

### Problems

1. Take a yardstick and balance it in the middle. Where is the fulcrum?

2. If a 2-lb. weight is attached 7 in. from the fulcrum, where should a 3-lb. weight be placed to balance it? Draw a sketch.

3. Examine common tools and devices, such as scissors, pliers, tack-lifters, lemon-squeezers, nutcrackers, can openers, pokers, etc., and measure the force arm and weight arms.

4. What is the weight or lift produced on a pump handle that has a weight arm of 5 in. and a force arm 21 in. long when 25 lbs. is applied at the handle? Draw a sketch.

6. A safety valve on a stationary boiler is loaded with a 50-lb. weight at W (Fig. 13). Distance F P is 4 in., P W, 12 in. Find the total steam pressure necessary to open the valve.