Science High School Reviewer | Grade 4 Science | Physical Science | Properties of Matter | Lesson 25: Measurement

How do we measure matter?
Measuring and counting squares is one
way to compare size. When we measure,
we use standard units. A standard unit is a
measurement on which people agree. Many
people in the United States use standard units
in the English system. The inch (in.), pound (lb),
and ounce (oz) are standard units in that system.
Scientists use standard metric units. The metric
system is based on units of ten. It uses prefixes
such as kilo-, centi-, and milli- to define the size
of measurements. For example, 1 meter (m) is
divided into 100 centimeters (cm). There are
1,000 meters in a kilometer (km).

Length and Width
An object’s length is the number
of units that fit from one end to the
other. Width is the number of units
that fit across. How wide is this
page? How long is it?
Area
Area (AYR•ee•uh) describes the
number of unit squares that cover a
surface. An easy way to find the area
of a rectangular shape is to multiply
its length by its width. The area of
this page, for example, is 27 cm × 20
cm, or 540 square cm (cm2).
What if a shape is not
rectangular? Divide it into smaller
squares. Find the area of each smaller
shape. You might need to estimate
parts of some shapes. Then add the
area of each smaller shape to find the
total area.

Volume
Volume describes the
number of cubes that fit
inside an object. To find the
volume of a rectangular solid,
just multiply its length by its width
and height.
If a solid is not rectangular, you
can use water. First, measure the
amount of water in a container.
Then, submerge the entire object
below the water. Subtract the
original water level from the new
water level. The result is the volume
of the object.
To find the volume of a liquid,
pour it into a measuring cup, spoon,
beaker, or graduated cylinder. Then
read the markings on the container.

What is density? (diagram, matter with different densities SACL G4)
A plastic ball floats on water.
If you fill the ball with sand, it will
sink. Why? The volume of the ball is
the same, but you changed its mass.
Sand has more mass than air.
Mass Divided By Volume
The relationship between mass
and volume is called density
(DEN•si•tee). Density is the amount
of matter in a given space. Scientists
define density as the amount of
mass in a unit of volume.
Density describes how tightly
matter is packed together. To find
the density of an object, divide its
mass by its volume. If the mass is
in grams and the volume in cubic
centimeters, then the result will have
units in grams per cubic centimeter
(g/cm3)

Density and Buoyancy
The density of an object also
affects its buoyancy. Remember,
buoyancy is the upward force of
a liquid or gas on another object.
Float or Sink?
Consider cork and water. The
density of water is 1 g/cm3. The
density of cork is 0.24 g/cm3. Does
cork float or sink?
An object floats when its density
is less than the density of the liquid
or gas in which it is placed. The
density of cork is less than the density
of water. So cork floats on water.
Liquids can float on top of water, too.
Can you change the density of
matter? If you add heat to air, the
air particles move more quickly.
They spread out more. The heated
air is less dense. It rises and floats
over the cooler, denser air.

What is weight?
Do you know your weight (WAYT)?
Weight is another way to measure matter.
Weight and mass may seem similar, but
they are not the same.
Mass is the amount of matter in an
object. Weight measures the amount of
gravity between an object and a planet,
such as Earth. Gravity is a force, or pull,
between all objects.
How are weight and mass related? The
force of gravity depends, in part, on an
object’s mass. The more mass, the stronger
the pull of gravity. The stronger the pull of
gravity, the more an object weighs.
Unlike mass, an object’s weight is
different on other planets and on the
Moon. The pull of gravity on the Moon
is about 16
as strong as on Earth. So an
object’s weight on the Moon is only 16
of
its weight on Earth.
Do you weigh yourself with a scale?
Mass is measured with a balance. Weight is
measured with a scale. Ounces and pounds
are the English units for weight. The
metric unit for weight is the newton (N).