MACHINES IN EVERYDAY LIFE 



157 



force or balance travel ? Record your results. 



Part 2. Rearrange the pulley, weight, and balance to be 

 like the diagram shown at B and repeat the measurements 

 made in the first part. Record your results. 



Part 3. Secure a pair of two-pulley blocks and set them 

 up as shown in the diagram at C. Attach the spring balance 

 as shown and a four-pound weight. Measure the effort 

 needed to lift the four- pound weight and also weights of 

 six and ten pounds. Measure the distance the effort force 

 or balance moves vertically in raising the load half a foot. 

 Record your results. 



Make the simple calculations indicated. 

 Part 1. 



Load = pounds. Effort = pounds. 



Load distance = 1 foot. Effort distance = feet. 



Load X load distance = 



Effort X effort distance = 



Part 2. 



Load = pounds. Effort = pounds. 



Load distance = 



Load X load distance = _ 



Effort X effort distance = 



feet. Effort distance = 

 foot pounds, 

 foot pounds. 



feet. 



The number of cords to the movable pulley = 



Part 3. 



Tabulate the data for Part 3 under the column headings 

 Load, Effort, Load Distance, Effort Distance, Output, and 

 Input. 



In a single fixed pulley the effort is (greater than, less 

 than, the same as) the load and therefore ad- 

 vantage is gained. 



The load distance is (equal to, greater than, less than) 

 the effort distance. 



In a single movable pulley cords support the load, 



and the effort is 



the load. This gives an advantage of 



The advantage gained by a pulley system over a load can 

 always be told by counting the which the load. 



In this experiment the work put into the machine was 



found by multiplying the by the The work put 



out by the machine was found by multiplying the by 



the These were nearly in all cases. The difference 



was due to The work (put in, got out) was al- 

 ways greater. 



Experiment 110. How does the inclined plane gain 

 an advantage and how may the advantage be 

 found? 



Read on page 161 the section on "How may machines be 

 made more efficient?" before doing this experiment. 



This experiment calls for a small car like the one shown 

 in the picture, but a toy railroad car may be used in its 



place. If neither of these is 

 available one can be made 

 from a chalk box with spools 

 for wheels. Secure a smooth 

 board at least three feet in 

 length and raise one end of it 

 six inches from the table top. 

 Weigh the car accurately and 

 then place a one-pound 

 weight or a one-pound bag of 

 sand in it. Attach a string and 

 FIG - 252 spring balance to the car as 



shown in Figure 252. De- 

 termine the average force used to pull a one-pound weight 

 and the car up the plane. Keep the balance parallel to the 



plane. Repeat, using weights of two and three pounds. Meas- 

 ure the length of the plane along its bottom edge up to the 

 support and the height from the table top to the bottom of. 

 the plane at the support. Record your measurements and 

 calculatfons in a table under the column headings Weight 

 of Car, tead, Total Load, Effort, Length, Height, Input 

 (Lcngtl^^Effort), Output (Total Load X Height). 



Make the height of the plane one foot and repeat all of 

 the measurements made in the previous case. Record your 

 results. 



Study the two data tables. How does the effort change 

 with the increased load? How does the effort change with 

 the increased height? What is the ideal mechanical ad- 

 vantage in each of the two cases? To find this, divide the 

 length of the plane by its height. What is the actual mechani- 

 cal advantage in each of the two cases? To find this, divide 

 the load by the effort. Can you account for the differences 



How does the work put into this machine (effort X 

 length) compare with the work got out of it (total load 

 X height) ? Why is there a difference? 



Determine the efficiency of this plane from each of the 

 two parts. (Divide the work got out by the work put in.) 



Problem. A man wishes to raise a heavy box into a truck. 

 He can use either a long or a short plank as an inclined 

 plane. State what he would gain and lose in the use of each. 

 f 



READINGS WHICH WILL HELP ANSWER 

 THE PROBLEM QUESTIONS 



What is work and how is it measured? We are liv- 

 ing in an age of machines. During the past two hun- 

 dred years the world has been changed from a "hand" 

 world to a "machine" world. Today we ofttimes 

 prize the word "hand-made" on articles that we pur- 

 chase. Shall we live to see the "hand-made" a com- 

 pletely lost art? Our farmers no longer farm with the 

 hand plow, the scythe, and the cradle of a few gen- 

 erations ago. These farming implements have been 

 replaced by the gang plow, the mowing machine, and 

 the reaper. Even the horse, man's faithful servant, is 

 rapidly being replaced by the tractor. 



In the home we now perform with machines many 

 tasks formerly done by hand. Our means of trans- 

 portation have been changed by the introduction of 

 the automobile and airplane. It is no wonder that this 

 is called the "machine age." 



With all of their complexity, modern machines are 

 really only combinations of two very simple machines 

 which have been known to man for many ages. These 

 are the lever and the inclined plane. By combining 

 these into intricate and involved machines man has 

 been able to overcome many of the resisting forces 

 of nature. 



Machines are able to help us in modern life because 

 they aid us in applying force and in gaining speed. 

 In the use of machines to conquer the forces of na- 

 ture, the scientist has learned how to measure the 

 work done by machines. Let us see how he accom- 

 plishes this. 



