How are mass and weight measured?
Objective: 1)Identify the SI unit of mass. 2)Compare mass and weight.
Vocabulary
Kilogram – basic unit of mass
Mass – amount of matter in an object
Weight – measure of the pull of gravity on an object
Mass
The amount of matter in an object is its mass. There is
more matter in a bag of potatoes than in a bag of
popcorn. The bag of potatoes has more mass.
The basic unit of mass in the metric system is the
kilogram (KIL-uh-gram) (kg). The gram (g) is a smaller
unit of mass. Chemists often use grams when measuring
chemicals. Remember that the prefix “kilo-” means
1000. There are 1000g in 1 kg.
Identify: What is the basic metric unit of mass?
Mass and Weight
Mass and weight are related, but they are not the
same. Weight is a measure of the pull of gravity on
an object. Gravity is a force of attraction between all
objects. The force of gravity depends on the mass of
the objects and how far apart they are. Objectives
with a large mass have a strong force of gravity. As
objects move farther away from each other, the force
of gravity between them becomes less. On earth, the
force of gravity pulls all objects toward the center of
the earth.
Weight can change because the pull of gravity is not
the same everywhere. For example, the moon has less
mass and less gravity than the earth. An Astronaut on
the moon would weigh less than on the earth.
However, the astronaut’s mass would not change. The
mass of an object always remains the same.
Describe: What does weight measure?
Measuring Mass
Mass is measured with an instrument
called a balance. A balance works like
a seesaw. It compares an unknown
mass with a known mass. One kind of
balance is a triple beam balance. A
triple-beam balance has a pan on which
the object being measured is placed. It
also has three beams. Weights, or
riders, are moved along each beam
until the object on the pan is balanced.
Each rider gives a reading in grams.
The mass of the object is equal to the
total readings of all three riders.
Lesson Summary
•Mass is the amount of matter in an object.
•The basic unit of mass in the metric system is the kilogram.
•Weight is a measure of the pull of gravity on an object.
•The weight of an object can change, but its mass remains the same.
•A balance is used to measure mass.
Check
Write true if the statement is true. If the statement is false, change the
underlined term to make the statement true.
1.
The amount of matter in an object is its weight.
2.
The basic unit of mass in the metric system is the gram.
3.
A balance is used to measure mass.
4.
There are 100 grams is one kilogram.
5.
An astronaut would weigh less on the moon than on the earth.
6.
Weight is a force of attraction between all objects.
Apply
Complete the following.
7. Compare: What is the difference between mass and weight?
8. Calculate: Your weight on the moon would be only about one-sixth your
weight on the earth. How much would you weigh on the moon?
9. Infer: The mass of mars is about one-tenth the mass of earth. Would an
astronaut weigh more on Mars or Earth? Explain.
10. What unit would you use to measure the mass of a potato?