PHYSIOLOGY FOR BEGINNERS 



Physical Preliminaries 



When a man does work or makes any muscular effort he 

 is exerting what is called force. Similarly, force is exerted 

 by any machine, apparatus, or thing which sets anything in 

 motion, or brings to rest anything that was previously in 

 motion. 



When a force is exerted so as to move anything, the force 

 is opposed, and is said to meet resistance. A cannon ball 

 flying through the air meets no resistance (we here neglect 

 the slight resistance of the air) till it strikes some object, and 

 then, but not till then, does it exert force. A travelling steam- 

 engine is exerting force against the resistance of the track and 

 of the air. This resistance with that of the moving parts 

 of the engine is tending to stop the engine, and when the 

 steam is shut off will gradually stop it. The resistance is 

 therefore a force. Thus one force is always opposed by 

 another force. 



When a weight is resting on a table it exerts a force on the 

 table due to its tendency to fall, owing to the attraction of the 

 earth, or gravity. The weight does not fall because it is 

 opposed by an equal force' the resistance of the table. In 

 this case the two forces are acting towards each other, and 

 mutual pressure is said to be produced. If the weight is 

 suspended by a string, the weight and the resistance act away 

 from each other, and tension is said to be produced in the 

 string. The resistance exerted by the surface of one thing to 

 the motion of another thing moving over it, and in contact 

 with it, is called friction. The rougher the surfaces, the 

 closer the contact, and the greater the pressure between the 

 two things, the greater will be the friction. 



The "weight of an object is the force with which the 

 object is attracted to the earth. If a man is to raise a heavy 

 object he must exert a force greater than its weight When 

 he has succeeded in raising the object he is said to have 

 done a certain amount of "work. All the time the man was 

 attempting to raise the weight, he was exerting force, but 

 until he moved it he had not accomplished any work. Work 

 is performed only when some effect is produced. The power 

 to do work which anything possesses is called its energy. 



