Weight, Mass, and Volume8.1

WEIGHT AND MASSYou’ve probably weighed yourself at home, at thedoctor’s office, or in the gym. But what does thatnumber mean?

Weight is a measure of how strongly gravity pulls onsomething. Earth has a stronger gravitational pull thanthe Moon. Therefore, an object’s weight on the Moonis less than its weight on Earth.

Look at Figure 1. On Earth, gravity would make thisequipment too heavy for the astronaut to carry. Inspace, the equipment is much lighter because theforce of gravity is not as strong.

Key Question: What are the relationships

among weight, mass, and volume?

weight

the force of gravityacting on an object

Figure 1 The astronaut can move huge pieces of equipment because they appearto be weightless in space.

164 Chapter 8 Worksheet 8.1-1 Copyright © 2010 by Nelson Education Ltd.

more gravity � more weight less gravity � less weight

1000 cm3 = 1000 mL = 1 L

1 cm3 = 1 mL

1 cm

1 cm1 cm

10 cm

10 cm

10 cm

Figure 2 The basic unit for measuring volume is the litre.

Mass can be measured in kilograms. A kilogram ofgold and a kilogram of foam have the same mass.However, you need much more foam than gold tomake up a kilogram. Their masses are the same, butthe volume of foam is greater.

VOLUMEVolume measures how much space an object orsubstance takes up. You can measure the volume of anobject with a regular shape, such as a cube. Multiplythe object’s length, width, and height together. Theanswer will be in cubic units (m3, cm3, and so on).

Look at the cube in Figure 2. The length, width, andheight 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

Volume � length � width � height

volume

the amount of space an object orsubstance takes up

Millilitres (mL) are used to measure small volumes ofliquids.

1 L � 1000 mL.

1 mL � 1 cm31000 cm3 � 1 L � 1000 mL

Mass is different from weight. Mass measures theamount of matter in something. The amount of gravitydoes not change the amount of mass. So, an object’smass would not change on the Moon, even though itwould have a different weight.

mass

the amount of matterthat makes up anobject or substance

TURNChapter 8 Worksheet 8.1-1 165Copyright © 2010 by Nelson Education Ltd.

FINDING VOLUME BY DISPLACEMENTCubes have a regular shape. It is easy to measure theirlength, width, and height in order to find the volume.But what about objects like rocks, with irregularshapes? How would you find a rock’s volume?

You can use the displacement method to find thevolume of objects with irregular shapes. To displace

means to take the place of something. Objects put intoa fluid displace the fluid.

These steps describe one displacement method:

1. Fill an overflow can with water until it begins tooverflow.

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 thatoverflowed.

The volume of water that overflowed is equal to thevolume of the object.

Figure 3 shows a student using an overflow can tomeasure the volume of an object.

Figure 3 This student measures volume using an overflow can.

displace

to take the place of

166 Chapter 8 Worksheet 8.1-1 Copyright © 2010 by Nelson Education Ltd.

1. (a) How is the weight of an object on the Moon different from its weight onEarth?

(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.

CHECK YOUR UNDERSTANDING

What it measures Units of measure

Weight

Mass

Volume

Chapter 8 Worksheet 8.1-1 167Copyright © 2010 by Nelson Education Ltd.

END

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