8.1
Weight, Mass, and Volume
Key Question: What are the relationships
among weight, mass, and volume?
WEIGHT AND MASS
You’ve probably weighed yourself at home, at the
doctor’s office, or in the gym. But what does that
number mean?
weight
the force of gravity
acting on an object
Weight is a measure of how strongly gravity pulls on
something. Earth has a stronger gravitational pull than
the Moon. Therefore, an object’s weight on the Moon
is less than its weight on Earth.
more gravity ⫽ more weight
less gravity ⫽ less weight
Look at Figure 1. On Earth, gravity would make this
equipment too heavy for the astronaut to carry. In
space, the equipment is much lighter because the
force of gravity is not as strong.
Figure 1 The astronaut can move huge pieces of equipment because they appear
to be weightless in space.
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mass
the amount of matter
that makes up an
object or substance
Mass is different from weight. Mass measures the
amount of matter in something. The amount of gravity
does not change the amount of mass. So, an object’s
mass would not change on the Moon, even though it
would have a different weight.
Mass can be measured in kilograms. A kilogram of
gold and a kilogram of foam have the same mass.
However, you need much more foam than gold to
make up a kilogram. Their masses are the same, but
the volume of foam is greater.
VOLUME
volume
the amount of
space an object or
substance takes up
Volume measures how much space an object or
substance takes up. You can measure the volume of an
object with a regular shape, such as a cube. Multiply
the object’s length, width, and height together. The
answer will be in cubic units (m3, cm3, and so on).
Volume ⫽ length ⫻ width ⫻ height
Look at the cube in Figure 2. The length, width, and
height are each 10 cm. The volume of the cube is
1000 cm3 or one litre (L).
10 cm ⫻ 10 cm ⫻ 10 cm ⫽ 1000 cm3 ⫽ 1 L
1000 cm3 = 1000 mL = 1 L
10 cm
10 cm
10 cm
1 cm3 = 1 mL
1 cm
1 cm 1 cm
Figure 2 The basic unit for measuring volume is the litre.
Millilitres (mL) are used to measure small volumes of
liquids.
1 L ⫽ 1000 mL.
1000 cm3 ⫽ 1 L ⫽ 1000 mL
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1 mL ⫽ 1 cm3
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TURN
FINDING VOLUME BY DISPLACEMENT
Cubes have a regular shape. It is easy to measure their
length, width, and height in order to find the volume.
But what about objects like rocks, with irregular
shapes? How would you find a rock’s volume?
displace
to take the place of
You can use the displacement method to find the
volume of objects with irregular shapes. To displace
means to take the place of something. Objects put into
a fluid displace the fluid.
These steps describe one displacement method:
1. Fill an overflow can with water until it begins to
overflow.
2. Wait until the overflowing stops.
3. Place a container under the spout of the overflow can.
4. Place the object into the water.
5. Collect and measure the volume of water that
overflowed.
The volume of water that overflowed is equal to the
volume of the object.
Figure 3 shows a student using an overflow can to
measure the volume of an object.
Figure 3 This student measures volume using an overflow can.
166 Chapter 8 Worksheet 8.1-1
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Name:
_________________________________________
Date: ________________________
CHECK YOUR UNDERSTANDING
1. (a) How is the weight of an object on the Moon different from its weight on
Earth?
(b) Why is it different?
2. Describe how to measure the volume of an irregular solid.
3. Think back to the Key Question. Fill in the table to compare weight, mass,
and volume.
What it measures
Units of measure
Weight
Mass
Volume
Copyright © 2010 by Nelson Education Ltd.
Chapter 8 Worksheet 8.1-1 167
END