Mass and Weight.
How are weight and force related?
Measuring Mass and Weight
Weight is a measure of the force or pull of gravity on a body. Your own weight is the force of gravity
that pulls you down to Earth. Weight may be measured with a spring scale. The unit of force in the metric
system is the newton (nt).
Mass is the amount of material in a body. Mass does not depend on gravity. The more you weigh, however,
the more mass you have. Mass may be measured with a
pan balance.
A body of unknown mass is placed on the left pan of the
balance. Metal pieces of known mass are placed on the right
pan. When the unknown and known bodies balance, they
both have the same mass. The total mass of the pieces
on the right pan is the mass of the object on the left pan.
The gram (g) is the unit of mass in the metric system. One
kilogram is equal to 1000 grams. Remember, the prefix
kilo- means 1000. A mass of one kilogram weighs
about 2,2 pounds.
One page of this book has a mass about 3,25 g.
A cubic centimeter of water has a mass of about 1 g.
Figurе 1-15. The international standard of mass is а platinum-Iridium
cylindor. Tho cylindor has a mass of exactly one kllogram.
Weight and Mass
All things are attracted to the earth. A skydiver leaping from an
airplane falls swiftly toward the ground. Jump up in the air and you
come down again. If you accidentally let go of a ball during a game,
it falls to the ground. Bodies fall because the earth exerts a force on
them. This force is gravity. Gravity acts upon all bodies on or near
the earth's surface. The force of gravity is measured by weight.
You can measure weight with a spring scale. Measurements are
made using newtons in the metric system. Pounds and ounces are
the units for measuring force in the English system.
ACTIVITY. You can measure the force of gravity with a
spring.
(1)
Cut off the bottom half of a paper cup. With a small
piece of string, attach the cup bottom to a spring.
Tie the opposite end of the spring to a clamp supported by a ring
stand. Bend a paper clip to form a pointer and attach it to the
bottom end of the spring . Attach a piece of cardboard in back of the
spring with masking tape. Mark a zero on the cardboard opposite
the pointer. Now place a metal washer in the paper cup.
Mark the new position of the pointer. Add a second washer and
mark the new position of the pointer. Repeat this procedure until you
have a total of ten washers in the cup. Mark the scale each time.
DO NOT OVERLOAD THE SPRING. Why?
Remove the washers from the cup.
(2)
Now weigh separately a marble, thimble, pencil, and pen.
Read and record the weight of each in terms of your washer-weight
scale. Which weighed the most? Why aren't washers used as standard units of force?
Mass is different from weight. Mass the quantity or amount of matter in an object.
Notice that it has a definite mass and occupies space. Gases and liquids also have definite mass and occupy
space. Anything that occupies space and has mass is called matter. Unlike weight, the mass of a given body
remains constant.
How is weight measured?