34 APPLIED SCIENCE 



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 Ibs. 

 is applied at the handle? Draw a sketch. 



5. 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. 



