26 ELEMENTS OF LABORATORY WORK 



. Additional Exercises and Questions. 



1. Why are two lines at least needed in order to define the position 

 of a particle in a given plane ? 



2. Compare the above method of defining position with that of using 

 angles. Give diagrams. 



3. Show by diagrams that the position of one point in a given plane 

 with regard to another requires either two lines at right angles, or two 

 lines drawn from these points to a third, before any description of that 

 position can be given. 



4. There are four points in the circumference of a circle which are 

 similarly situated with regard to any two diameters drawn at right 

 angles. How may their position with regard to one another be 

 described ? 



5. How may the position of a given area be defined ? 



6. Draw a diagram defining the position of four particles in the same 

 plane with regard to each other, that is, describe the configuration of 

 such a system of particles. 



7. Represent, by three sheets of paper or three books, three planes 

 at right angles to one another. 



8. Measure on the model planes the distance from each of a small 

 body supported on a wire. Use a piece of string and a scale for 

 measurement. Also measure from the squares by eye. 



9. Place several bodies on the model to represent the different posi- 

 tions at different moments of a given body, and bend a wire to show 

 the probable path of the body. W r hat conditions must be assumed 

 before this path can be taken as the true one ? 



10. Fix wires to show the various paths in which a particle may 

 move with regard to the model. 



11. Fix wires which shall represent the possible paths of a portion 

 of a large body. How would they be altered if the shape of the body 

 were changed during the displacement ? 



12. Show that every portion of a rotating body moves in the second 

 or third mode stated as possible for any particle, that is, either in a 

 plane or non-planar curve. 



22. Rate of Change of Position. When both the extent 

 and duration of a given displacement are observed we become 

 conscious of motion. 



The unit of time is the second. If a displacement of a metre 

 along the straight line joining two particles occurs in a second, 

 or of two metres in two seconds, and so on, then if one of the 

 particles be considered as fixed, the other is said to be in motion 



