MOTION* 1 1 



merable. A ship impelled by the wind and tide is 

 well known. A paper kite acted upon by the 

 wind and the string, is another. 



A body is said to have an uniform motion, when 

 it moves over equal spaces in equal times. Motion 

 is said to be accelerated, if its velocity con- 

 tinually increases ; to be uniformly accelerated, if 

 its velocity increases equally in equal times. 



If we suppose a body to be put in motion by a 

 single impulse, and moving uniformly, to receive a 

 a new impulse from the same direction, its velocity 

 will be augmented, and it will go on with the 

 augmented velocity. If at each instance of its 

 motion, it receive a new impulse, the velocity will 

 be continually increasing ; and if this impulse be 

 always equal, the velocity will be uniformly 

 accelerated. 



Motion is said to be retarded, if its velocity con- 

 tinually decreases ; and to be uniformly retarded, 

 if its velocity decreases equally in equal times. 



Motion has been also divided into absolute and 

 relative. 



Absolute motion is the change of absolute place, 

 or the application of a body to different parts of 

 infinite and immoveable space. 



Relative motion is a change of the situation of the 

 body with respect to other bodies. 



These two kinds of motions may be explained in 

 the following manner: were the earth immoveably 

 fixed, then a boat going down a river would be in 

 absolute motion, while a man sitting on the deck 

 would partake of this motion, yet he would not 

 change his situation with respect to the parts of the 

 boat. 



Again, if the man were to walk on the deck 

 from the stem to the stern, just as fast as the boat 



