130 ELEMENTARY GENERAL SCIENCE CHAP. 



CHIEF POINTS OF CHAPTER IX. 



Work is the act of overcoming resistance, or causing change of 

 velocity. 



The Principle of Work. Work is done by a force when the point 

 of application moves through a certain distance. 



Work done = force x distance. 



A Foot-pound is the work done when a force equal to the weight 

 of one pound is exerted through a distance of one foot in the direction 

 of the force. 



Power, or the rate of doing work, is measured by the number of 

 foot-pounds produced in a given time. A horse-power is equal to 

 33,000 foot-pounds per minute. 



Energy is the ability to do work. 



Energy. 



Kinetic, Potential, 



due to motion as due to position, 



shown by a moving as a mass, at the top 



cannon-ball and a of a tower and a 



flowing river. wound-up spring. 



Sound, produced by vibrations of material sub- 

 stances. 



Heat, produced by motions of molecules. 

 Radiation, due to vibration set up in the ether, 

 and producing the effects of radiant light, 

 heat, &c. 



,coba,b Electrification, evidenced by the action of elec- 



Enerer trifled bodies upon one another. 



**" Electricity in motion, as in the electric current, 



which can be transformed into light, heat, or 

 motion. 



Chemical action, used to produce light and heat 

 when a fire burns, and to produce motion in a 

 gas-engine. 



Manifestations 



Measurement of Kinetic Energy. Kinetic energy is equal to one- 

 half the product of the body's mass and the square of its velocity. 

 But the mass and the velocity must be expressed in suitable 

 units. 



Conservation of Energy. Energy is never lost, but only changed 

 in form, and whatever transformations take place, the sum total of 

 kinetic energy and potential energy remains the same. 



