Download Forces and Friction Worksheet (Key)

Name: ______________________________ Class: ____ Date: ________________
FORCES
Key Concept: Like velocity and acceleration, a force is described by its strength
and by the direction in which it acts.
• A force is a push or a pull.
• To tell about a force, you must tell how strong the force is. The SI unit for the
strength of a force is the newton.
• To tell about a force you must also tell the direction the force is pushing or pulling.
• Arrows can be used to show forces. The point of the arrow shows the direction
of the force. The length of the arrow shows how strong the force is.
Answer the following questions. Use your textbook and the ideas above.
1. Circle the letter of the arrow that shows the stronger force. B
2. True or false? Forces are described by their strength and their direction.
True
3. The SI unit used for measuring the strength of a force is the newton.
4. Read the words in the box. Use the words to fill in the concept map about force.
Forces
Strength
Direction
/
are described by
\
Key Concept: Unbalanced forces acting on an object result in a net force and
cause a change in the object’s motion. Balanced forces acting on an object do
not change the object’s motion.
• Often there is more than one force acting on an object. The total of all the
forces acting on an object is called the net force.
• Sometimes the net force on an object is 0. This means there are balanced
forces acting on the object. The object’s motion does not change.
• Sometimes the net force does not equal 0. This means there are
unbalanced forces acting on the object. The object’s motion changes.
Answer the following questions.
5. Draw a line from each term to its meaning.
Term
Meaning
net force b
a. cause a net force of 0
balanced forces a
b. the total of the forces acting on an object
unbalanced forces c
c. cause an object’s motion to change
6. Label the circles in the Venn diagram to show which circle describes
balanced forces and which circle describes unbalanced forces.
Unbalanced Force
Balanced Force
net force not = 0
change in an
object's motion
net force = 0
a force
no change in an
object’s motion
objee
no change in an
object's motion
Friction
Key Concept: The strength of the force of friction depends on two
factors: how hard the surfaces push together and the types of
surfaces involved.
• Friction is a force caused by two objects rubbing together. Friction acts in
the opposite direction of motion. Friction keeps you from slipping when you
walk. Friction also makes a car’s brakes work.
• The amount of friction depends on two things: how smooth the objects are
and how hard they push together.
• There are four kinds of friction:
1. Static friction is between two things that are not moving.
2. Sliding friction happens when two objects slide past each other.
3. Rolling friction occurs when one object rolls over another.
4. Fluid friction happens when a solid moves through a fluid, like water or
air.
Answer the following questions. Use your textbook and the ideas above.
1. A force caused by two objects rubbing together is fricition.
2. Circle the letter of each sentence that is true about friction.
a. Friction acts in the same direction as motion.
b. There are four kinds of friction.
c. The amount of friction depends only on how smooth the objects are.
3. Friction acts in the opposite direction of the object’s motion.
4. Read the words below. Use the words to fill in the blanks in the table about
friction.
Static friction (c)
Fluid friction (a)
Sliding friction (b)
Key Concept: Two factors affect the gravitational attraction between objects:
mass and distance.
• Gravity is a force that pulls objects toward each other.
• Gravity depends on mass. Mass is how much matter is in an object. Objects
with a large mass have a greater force of gravity than objects with a small
mass.
• Gravity depends on distance. As the distance between objects increases, the
force of gravity decreases.
• Weight measures the force of gravity on an object. An object’s weight can
change if the force of gravity changes. An object’s mass stays the same no
matter where it is.
Answer the following questions. Use your textbook and the ideas above.
5. A force that pulls objects toward each other is gravity.
6. Read each word below. In each sentence below, fill in the correct word or
words.
increases
decreases
stays the same
a. If two objects move farther apart, the force of gravity between them
decreases.
b. An object’s mass stays the same if less gravity acts on the object.
7. What is weight? Circle the letter of the correct answer.
a. a force that pulls objects toward each other
b. the amount of matter in an object
c. the force of gravity on an object
Key Concept: In free fall, the force of gravity is an unbalanced force that
causes an object to accelerate.
• Gravity is the force that pulls objects toward Earth.
• If gravity is the only force pulling on a falling object, the object is in free fall.
• Most objects move through air. Friction caused by air is called air resistance.
Air resistance is a force that pushes upward on falling objects.
• As an object falls to Earth, its velocity increases. The greatest velocity it
reaches is called its terminal velocity.
Answer the following question. Use your textbook and the ideas above.
8. Read the words in the box. Use the correct words to label the forces in the
picture.
a. gravity
b. air resistance