Man's physical universe

xanabras

236 PHYSICAL LIMITATIONS HAVE BEEN OVERCOME

shown in Fig. 73A. Such a curve is called a probability cnri'e. Similar

curves are found in the graphical expression of the grades made in

college by a large number of students; in fact, many schools require

that the greides of large classes conform to the probability curve. One

2500 -

E 2000

34 36 38 40 42 44 46 48 60 12

Chest Measurement

3

Velocity of Molecules

Fig. 73A. The curve of variation Fig. 73B. The theory of probaof

the chest measurements of Scottish bility shows that molecules subject

soldiers. to chance collisions may be divided

into groups, each one with a different

range of velocity.

can expect to find in almost any large group of people a large number

of ordinary people and a small number of idiots and men of genius.

Similar curves may be drawn to illustrate the distribution of hits on a

target or the heights and weights of men of a certain age.

The theory of probability can be applied to the speed of molecules

and the frequency of their collision. Calculations show that when the

average speed is one mile per second, then —

About one molecule in every

700,000

5

2

50,000

150,000,000

less than

less than

has a speed of

0.01 miles per second

0.5 miles per second

0.7-1.3 miles per second

more than 3 miles per second

more than 4 miles per second

7. In what directions do molecules move?

Answer: Molecules move along straight lines in all conceivable

directions.

8. Do molecules ever collide with each other, and if so, what is the

result?

Answer: Molecules of gases collide with each other and with the

walls of a container very frequently. Although molecules of a gas may

be moving w^ith a speed of one mile per second, they actually travel an

average of only 1/60,000 centimeter before hitting another molecule

at atmospheric pressure. This means that an average hydrogen molecule

is hit by other molecules in one second as many times as a clock

ticks in seventy years.

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