Scientific English 2

STANDARDS OF MEASUREMENT

   In early times, measurements were made by comparing things with parts of the human body. Early units of measurement included the distance from the elbow to the fingers, the width of the hand and the width of the fingers.

   Some of these human measurements are still used. For example, the inch is based on the length of half the thumb. A foot was originally the length of a man's foot. A mile was one thousand walking steps.

   These units were only approximate, because their standard -the human body- was not constant. Governments tried to standardize them by using rods of fixed lengths. But these rods still varied from country to country.

   During the french revolution, scientists looked for a standard of measurement which did not change. They chose the distance from the Equator to the North Pole, which is one quarter of the circumference of the Earth. One ten-millionth of this was called one meter and became the basic unit of the metric system. Other metric units are based on it.. For example, the centimeter is one hundredth of a meter.

   A standard meter is marked on a platinum bar. The accuracy of measuring instruments was checked by comparing them with this bar. Nowadays, the meter is standardized by comparing it with another constant: the wavelength of a certain kind of light.

Now complete these sentences:

1- .................. included the distance from elbow to fingers, width of hand, width of finger.

2- .................. include the inch, the foot, the mile.

3- These .............. measurements were not ............ because ............... were used to standardize them, but they also varied.

4- .............. was chosen as the basic unit of ................ . Its length is ................ of ............ the Earth circumference. Other metric units are .................... .

5- The standard meter is marked on .................. . Nowadays, another constant is used: .................... .

AMAZING PHYSICS (Electrostatics)

Two oppositely charged particles, an alpha particle with 2 positive charges and a less-massive electron with a single negative charge, are attracted to each other. 

1- Compared to the force that the alpha particle exerts on the electron, the electron exerts a force on the alpha particle that is:

a) greater                                                b) the same                                     c) smaller

2- The particle with the most acceleration is the:

d) alpha particle                                      e) electron                                     f) same for each

3- As the particles get closer to each other, each experiences an increase in:

g) force                                                    h) speed                                        i) acceleration

j) all of the above                                     k) none of the above

ANSWERS:

b) the same                                             

e) the electron

j) all of the above

EXPLANATION:

a) By Newtons's 3rd law, the particles pull each other  with equal and opposite forces.

b) By Newton's 2nd law, for the same force, the particle with less mass undergoes more acceleration.

c) By Coulomb's law, as the separation distance is decreased, the force increases. By Newton's 2nd law, as the force increases, the acceleration increases. Since the particles accelerate toward each other, their speeds increase also.