s8pe-10401-ca
12/20/05
7:23 PM
MAZER
Page 103
KEY CONCEPT
Density is mass per
unit volume.
CALIFORNIA
Content Standards
8.8.a Students know
density is mass per unit
volume.
8.8.b Students know how
to calculate the density of
substances (regular and
irregular solids and liquids)
from measurements of
mass and volume.
8.7.c Students know
substances can be classified by their properties,
including their melting
temperature, density,
hardness, and thermal
and electrical conductivity.
BEFORE, you learned
NOW, you will learn
• The gravitational force an
object can exert depends on
the object’s mass
• Weight is defined as the force
gravity exerts on an object
• Weight depends on mass
• How to measure mass and
volume
• How mass, volume, and density
are related
• How to calculate density
EXPLORE Similar Objects (8.8.a)
How can two similar objects differ?
MATERIALS
PROCEDURE
1
Look at the two balls but do not pick
them up. Compare their sizes and shapes.
Record your observations.
2 balls of
different sizes
2 Pick up each ball. Compare the way the balls feel
in your hands. Record your observations.
VOCABULARY
WHAT DO YOU THINK?
volume p. 103
density p. 105
How would your observation be different if the larger
ball were made of foam?
Objects have mass and volume.
VOCABULARY
You might want to make a
magnet word diagram for
volume.
All objects are made up of matter. Matter can be defined as anything
that has mass and takes up space. Mass is the measure of the amount of
matter an object contains. Different objects contain different amounts
of matter. An elephant has more mass than a mouse. A metal fork has
more mass than a plastic fork.
Matter also has volume. Volume is the measure of the amount of
space an object takes up. An elephant has a greater volume than a
mouse because the elephant takes up more space. A metal fork and a
plastic fork might take up the same amount of space. In this case, the
two forks would have the same volume although they have different
masses. Often the volume of an object includes other substances inside
the object. For example, the volume of a basketball is the volume the
whole sphere takes up. The volume of the outside material is only a
part of this. Most of the volume is taken up by air.
check your reading
What is mass? What is volume?
Chapter 4: Density and Buoyancy 103
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