30 ELEMENTS OF LABORATORY WORK 



in spite of the several causes tending to move it. It is frequently 

 needed to find the causes which will be effective in keeping 

 the equilibrium of a body in opposition to causes which may 

 tend to displace it in various directions and at various rates. 

 Those conditions will be effective under which the body would 

 acquire a displacement equal and opposite to that which would 

 be the resultant of the other displacements. 



It will afterwards be found that these considerations will 

 sometimes be brought to bear upon important problems which 

 require the above processes to be reversed. We frequently 

 require to resolve a given displacement into its components 

 that is, to ascertain what other displacements would find in this 

 given displacement their own resultant. And most commonly 

 these displacements require to have directions which are at right 

 angles. 



The construction of a few diagrams will show that a given 

 displacement may result from an infinite variety of component 

 displacements, and consequently a given displacement may be 

 resolved into an infinite variety of components. 



Additional Exercises and Questions. 



1. How is it determined whether the velocity of a body is uniform 

 or variable ? 



2. What is the unit of velocity in the C.G.S. system ? What would 

 be the displacement in three minutes of a body moving uniformly with 

 a velocity of seven ? 



3. Show by a diagram that a single act of displacement may 

 produce the same result as two or more successive displacements. 



4. What will be the joint effect of several causes, each of which sepa- 

 rately would produce the same displacement in the same direction ? 

 What would be the condition of a body acted upon by causes which 

 tend to move it in exactly opposite directions ? 



5. By what processes would you trace the real path with regard to 

 the earth of a person walking on the deck of a ship in motion (1) for- 

 ward, (2) aft, (3) from side to side ? Draw diagrams and state the data 

 required for calculating his velocity with regard to the earth in each 

 case. 



6. What will be the condition of a body which is acted upon at the 

 same moment by causes which would,, if they acted in succession, pro- 

 duce in it during equal intervals the displacement represented in direc- 

 tion and magnitude by the three sides of a triangle taken in order ? 



