ANSWER KEY
POSSIBLE SHORT ANSWER QUESTIONs
1. A marble is lying in the middle of the floor.
Use Newton’s first law to describe what will
happen to the marble.
It will remain at rest. An object at rest will
remain at rest and an object in motion will
remain in motion unless acted upon by an
unbalanced force.
2. A broom strikes the marble while you are
sweeping. Use Newton’s second law to
describe what happens to the marble.
The marble will accelerate in the direction
that the broom hits it.
3. Use Newton’s third law to describe what
interaction there is between the marble and
the broom.
The marble pushes back on the broom with
an equal but opposite reaction. When one
object exerts a force on another object, the
second object exerts an equal but opposite
force back on the first object.
4. Why could it be important to use velocity
instead of speed when you describe how a
storm is moving?
If you know the velocity of the storm, you
know the direction of movement, which can
be used to warn people in the path of the
storm.
5. Use the diagram below to answer the
following questions.
a. What happens in the rocket engine at
point A? How does the rocket take off?
Include these terms in your answer: action
and reaction force, acceleration, force, and
gravity.
The rocket burns fuel and produces gases.
The rocket pushes these gases downward,
causing an action force. At the same time,
the gases apply an equal reaction force to
the rocket, pushing it upward. The force
provided by the rocket exceeds the force
of gravity, causing the rocket to
accelerate.
b. What is happening to the rocket at point
B? Explain what keeps the rocket from
falling back to the surface or moving off into
space.
The rocket is in orbit. If there was no
gravity, the rocket’s inertia would cause
the rocket to move in a straight line. But
the centripetal force of Earth’s gravity
causes the rocket to fall toward the center
of Earth.
6. An astronaut throws a baseball on the moon,
where there is no air. Back on Earth, you
throw an identical baseball using the same
force that the astronaut used to throw her ball.
Which ball will travel a greater distance
before it hits the ground? Explain.
The ball thrown on the moon will travel a
greater distance. Air resistance will slow
down the ball on Earth, but not the ball on
the moon. In addition, the force of gravity
will be greater on the ball on Earth. The
action of both of these forces (air resistance
and gravity) decreases the distance that a
thrown ball will travel before it hits the
ground.
7. You blow up a balloon and pinch the open
end closed. Predict what will happen when
you let go of the balloon in terms of Newton’s
third law of motion.
The balloon will move in a direction away
from its open end. When the balloon is
released, it returns to its original shape by
pushing air out of its open end. At the
same time, this air applies an equal force to
the balloon, pushing it in a direction away
from the open end.
8. If you move two objects farther apart, how
does the force of gravity between the two
objects change?
According to the law of universal
gravitation, the force of gravity between
the two objects will decrease. The greater
the distance between two objects, the
smaller the force of gravity between them.
9. How are weight and mass different?
Weight is the measure of the force of
gravity acting on an object, while mass is
the amount of matter in an object.
10. The Greek astronomer Ptolemy developed
the geocentric model of the solar system.
According to this model, planets and stars
orbit Earth. Use your knowledge of forces
and their effect of Earth’s motion to explain
why this model is incorrect.
Earth would have to be the object with the
greatest mass in the solar system in order
for the planets and the sun to orbit it.
However, the sun is the object with the
greatest mass, so it exerts the greatest
gravitational force on the planets. As a
result, planets orbit the sun.
11. Why are scientists concerned about ozone
depletion?
The ozone layer absorbs ultraviolet (UV)
radiation given off by the sun, preventing
UV rays from reaching Earth’s surface.
Too much UV radiation is harmful to living
things. If the ozone layer in the
atmosphere is depleted, living things on
Earth will be exposed to more UV radiation
from the sun.
12. What type of chemical pollutants are
responsible for ozone depletion? Where do
these chemicals come from?
Gases called CFC’s or chlorofluorocarbons
cause ozone depletion. CFC’s are used for
things like the cooling of refrigerators, air
conditioners, and freezers. When they leak
into the air, they rise slowly until they
reach the ozone layer.
13. What are the 3 R’s of conservation? Give
three examples of each.
Reduce – walk or ride a bike instead of
driving a car, take shorter showers, turn
off lights when leaving a room
Reuse – bring reusable bags to the grocery,
donate outgrown clothes to charity,
Recycle – recycle paper, plastic, aluminum
14. Why is conservation important?
Conservation is important to help preserve
resources and reduce pollution.
15. Explain the differences between renewable,
nonrenewable and inexhaustible energy. Give
an example of each.
Nonrenewable Energy – natural resources
that are used up more quickly than they
can be replaced (coal, oil, natural gas)
Renewable Energy – a natural resource
that is constantly recycled or replaced by
nature (biomass energy)
Inexhaustible Energy – a natural resource
that never runs out or gets depleted (wind,
solar, hydroelectric)