THE QUIZ SECTION 47

sized in the synchronous motor are: 1. both types of motor requiremanual impulse of a fairly high velocity to start them; 2. both varie-ties easily pull out of phase and stop. These motors are very sensitiveto load (friction). 3. position of the field is rather critical; 4. this typeof motor is reversible, but only by manual impulse; 5. no regulation ofspeed is possible, but the motor will run on sub-multiples of the im-pressed frequency.

It must be evident that all four of these investigations can neverbe accomplished in a single laboratory period. How much of this isto be adopted will depend on the nature of the course offered, whetherit is given as an appreciation course, or it is of a college preparatorynature. Much will depend on the attitude, maturity, and the skill ofthe students.

THE QUIZ SECTION

JULIUS SUMNER MILLERMichigan College of Mining ^ Technology^ Sault Ste. Marie, Michigan

1. A particle suspended by a string is pulled aside by a horizontal force.Show that no finite horizontal force can make the string perfectly horizontal.

2. A sphere laid upon a rough inclined plane of inclination 0 is on the pointof sliding. Show that the coefficient of friction is 2/7 tan 0.

3. A particle is dropped and one second later another particle is throwndewnward with an initial velocity of 10 ft/sec. When will they meet? Examinethe results!

4. A particle suspended from a fixed point by a string of length L is projectedhorizontally with a speed V^ Lg; show that when the string becomes slack theparticle has risen to a height 3/2 L.

5. Two men of different weights coast down a hill on identical bicycles.Which will reach the bottom first?

6. A small marble is allowed to ROLL from the top of a large sphere. A smallblock is allowed to SLIDE from the top of the sphere. Which leaves the spherefirst? Which lands farther from the sphere?

MORE SUNSHINE PUTS MORE SUGAR IN APPLESApples have more sugar if they get more sunshine during the growing season*

This was learned at CornelFs Agricultural Experiment Station in a long-timestudy aimed at correlating some of the factors like rainfall, amount of sunshine,and temperatures to the keeping quality of apples.Another discovery was that the higher the temperatures during the last six

weeks before harvest, the greater has been the amount of scald in storage. Thescientists will test this information further during the 1948-49 storage season,based on predictions made the last six weeks before harvest. Such knowledge, theysay, will be of value to growers, who could move scald-susceptible varieties out ofstorage rapidly if considerable scald were expected.