34 ELEMENTS OF LABORATORY WORK 



the piston-rod is converted into circular motion in the driving- 

 wheel, and this into the rectilinear movement of the loco- 

 motive by the friction of the rails. Every piece of mechanism 

 affords some illustration of change or constraint of motion. 



Additional Exercises and Questions. 



1. Bend a piece of wire so as to exhibit the path of any particle in 

 a nut moving upon a screw. How would you proceed to make your 

 model exactly represent the path of a certain particle upon a given nut 

 moving on a given screw ? Describe also the path of any particle in a 

 screw moving through a stationary nut. 



2. Ascertain by direct observation the paths of a particle in a wheel, 

 or round disc, rolling in a straight line. Draw it upon paper, and 

 explain its shape. 



3. What would be the path of every portion of a wheel which is 

 spinning and being moved in the direction of its axis ? 



4. Give examples of each kind of mechanical constraint of motion, 

 stating the mechanisms which exhibit them. 



5. How would you fix a given body so that it can move in a circle 

 which may lie in any plane ? 



6. Suggest a mechanism for converting one rotation into another 

 rotation at right angles. 



7. Show by means of a diagram (1) that when a rigid body is trans- 

 lated, every particle in it moves through an equal distance in the same 

 direction, and (2) that when a rigid body rotates, each particle does 

 not move through the same distance nor in the same direction. 



8. Make clear by diagrams and observations that any displacement 

 of a rigid system may be produced by a translation together with a 

 rotation of that system about any point in it. 



