APPLICATION OF FORCE. 87 



22. The sun Is 95 millions of miles from the earth, and ft requiiea 8 J minutes for Its 

 light to reach the earth ; with what velocity per second does light move J 



23. If a vessel sail 90 miles a day for 8 days, how far will it sail in that time ? 



24 A gentle wind is observed to move 1,250 feet in 16 minutes : how far would it move 

 in 2 hours, allowing 5,000 feet to the mile f 



25. What distance would a bird flying uniformly at the velocity of 60 miles per hour, 

 pass over in 12^ hours f 



26. Suppose light to move at the rate of 192,000 miles in a second of time, how lonj^a 

 time will elapse in the passage of light from the sun to the earth, the distance being 05 

 millions of miles 7 



27. What is the momentum of a body weighing 25 pounds moving with the velocity 

 •f 30 feet per second f 



28. A cannon-ball weighing 520 pounds, struck a wall with a velocity of 45 feet per 

 second : what was its momentum, or with what force did it striltc ? 



29. A locomotive and train of cars weighing 180 tons (403,200 pounds), and moving at 

 the rate of 40 miles per hour, came in collision with another train weighing 160 tons, and 

 moving at the rate of 26 miles per hour : what was the momentum, or force of collision ? 



30. A stone thrown directly at an object from a locomotive, moving at the rate of 3,520 

 feet per minute, was 2 seconds in the air ; at what distance beyond tho object did it 

 strike f 



CHAPTER VI. 



APPLICATION OF FORCE. 



What are the 174. The principal agents from whence we 

 Sf powe^'ifThl obtain power for practical purposes, are Men 

 •"■'si' and Animals, Water, Wind, Steam, and 



Gunpowder. 



The power of all these may be ultimately resolved into somo 

 ere ™ Natural °'^® ^^ more of the great natural forces, or primary sources of 

 forces are these power, viz., vital force, producing muscular energy, or strength 

 derived? ^° ^^^ ^^^ animals; gravitation, causing the flow of water; 



heat and molecular forces, the agents producing the power ex- 

 hibited by wind, steam, and gunpowder. 



Magnetism and electricity when called into action, and 

 Are there any ° •' . ^ r 



other agents of capillary attraction, are also agents of power; but none oi 



power? these are capable, as yet, of being used to any great extent. 



for tho production of motion. 



„ . 175. Muscular enerojy in men and animals 



ITowiamuseu- . n ■> • /• i 



lar energy ex- IS cxcrtcd Dv mcans of the contractiou 01 the 



crted t 



fibers which constitute the muscles of the 



