Chapter 4: Forces in One Dimension

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PHYSICS Principles and Problems
Chapter 4 Forces in One Dimension
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Forces in One Dimension
CHAPTER4
BIG IDEA

• Net forces cause changes in motion.

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Table Of Contents
CHAPTER4
Section 4.1 Force and Motion Section 4.2
Weight and Drag Force Section 4.3 Newtons
Third Law
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4
Force and Motion
SECTION4.1
MAIN IDEA A force is a push or a pull.
Essential Questions

• What is a force?
• What is the relationship between force and
  acceleration?
• How does motion change when the net force is
  zero?

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Force and Motion
SECTION4.1

• Review Vocabulary
• Acceleration the rate at which the velocity of an
  object changes.

• New Vocabulary
• Force
• System
• Free-body diagram
• Newtons second law

• Newtons first law
• Inertia
• Equilibrium

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Force and Motion
SECTION4.1
Force

• Consider a textbook resting on a table. To cause
  it to move, you could either push or pull on it.
• A force is defined as a push or pull exerted on
  an object.

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Force and Motion
SECTION4.1
Force (cont.)

• If you push harder on an object, you have a
  greater effect on its motion.
• The direction in which force is exerted also
  matters. If you push the book to the right, the
  book moves to the right.
• The symbol F is a vector and represents the size
  and direction of a force, while F represents only
  the magnitude.

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Force and Motion
SECTION4.1
Force (cont.)

• Forces can cause objects to speed up, slow down,
  or change direction as they move.
• Based on the definitions of velocity and
  acceleration, a force exerted on an object causes
  that objects velocity to change that is, a
  force causes an acceleration.
• All accelerations are the result of an unbalanced
  force acting on an object.

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Force and Motion
SECTION4.1
Force (cont.)

• When considering how a force affects motion, it
  is important to identify the object of interest.
  This object is called the system.
• Everything around the object that exerts forces
  on it is called the external world.

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Force and Motion
SECTION4.1
Force (cont.)

• Think about the different ways in which you could
  move a textbook.
• You could touch it directly and push or pull it,
  or you could tie a string around it and pull on
  the string. These are examples of contact forces.

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Force and Motion
SECTION4.1
Force (cont.)

• A contact force exists when an object from the
  external world touches a system and thereby
  exerts a force on it.

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Force and Motion
SECTION4.1
Force (cont.)

• There are other ways in which the motion of the
  textbook can change.
• If you drop a book, the gravitational force of
  Earth causes the book to accelerate, whether or
  not Earth is actually touching it. This is an
  example of a field force.
• Field forces are exerted without contact.

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Force and Motion
SECTION4.1
Force (cont.)

• Forces result from interactions thus, each force
  has a specific and identifiable cause called the
  agent.
• Without both an agent and a system, a force does
  not exist.
• A physical model which represents the forces
  acting on a system, is called a free-body diagram.

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Force and Motion
SECTION4.1
Force (cont.)
Click image to view movie.
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Force and Motion
SECTION4.1
Combining Forces

• When the force vectors are in the same direction,
  they can be replaced by a vector with a length
  equal to their combined length.
• If the forces are in opposite directions, the
  resulting vector is the length of the difference
  between the two vectors, in the direction of the
  greater force.
• Vector sum of all the forces on an object is net
  force.

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Force and Motion
SECTION4.1
Acceleration and Force

• To explore how forces affect an objects motion,
  consider the situation explored in the figure, in
  which, a horizontal force is exerted on an
  object.

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Force and Motion
SECTION4.1
Acceleration and Force (cont.)

• Notice, in order to reduce complications
  resulting from the object rubbing against the
  surface, the investigation was performed on a
  smooth, well-polished table and the cart has
  wheels.

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Force and Motion
SECTION4.1
Acceleration and Force (cont.)

• To exert a constant force, a spring scale was
  used to pull the cart.
• The velocity of the cart was measured for a
  period of time.
• Using the data, a velocity-time graph was
  constructed.

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Force and Motion
SECTION4.1
Acceleration and Force (cont.)

• The data indicates for a constant force there is
  a constant acceleration on an object.
• Thus, indicating the relationship between force
  and acceleration is linear and allowing the
  application of the equation for a straight line
• The y-intercept is 0, so the linear equation
  simplifies to ykx. The y-variable is
  acceleration and x-variable is force.

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Force and Motion
SECTION4.1
Acceleration and Force (cont.)

• What is the physical meaning of the slope of the
  acceleration-force graph?
• To determine this, increase the number of carts
  gradually.

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Force and Motion
SECTION4.1
Acceleration and Force (cont.)

• A plot of the force versus acceleration for one,
  two, and three carts indicates that if the same
  force is applied in each situation, the
  acceleration of two carts is the acceleration
  of one cart and the acceleration of three carts
  is the acceleration of one cart.

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Force and Motion
SECTION4.1
Acceleration and Force (cont.)

• This means that as the number of carts is
  increased, a greater force is needed to produce
  the same acceleration.
• The slopes of the lines in the graph depend upon
  the number of carts that is, the slope depends
  on the total mass of the carts.

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Force and Motion
SECTION4.1
Acceleration and Force (cont.)
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Force and Motion
SECTION4.1
Acceleration and Force (cont.)

• The formula, F ma, tells you that if you double
  the force, you will double the objects
  acceleration.
• If you apply the same force to several different
  objects, the one with the most mass will have the
  smallest acceleration and the one with the least
  mass will have the greatest acceleration.
• One unit of force causes a 1-kg mass to
  accelerate at 1 m/s2, so one force unit has the
  dimensions 1 kgm/s2 or one newton and is
  represented by N.

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Force and Motion
SECTION4.1
Newtons Second Law

• The observation that acceleration of an object is
  proportional to the net force exerted on it and
  inversely proportional to its mass is Newtons
  second law, which can be represented in the
  following equation.

• Newtons second law states that the acceleration
  of an object is equal to the sum of the forces
  (the net force) acting on the object, divided by
  the mass of the object.

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Force and Motion
SECTION4.1
Newtons Second Law (cont.)

• One of the most important steps in correctly
  applying Newtons second law is determining the
  net force acting on the object.
• Draw a free-body diagram showing the direction
  and relative strength of each force acting on the
  system.
• Then add the force vectors to find the net force.

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Force and Motion
SECTION4.1
Newtons Second Law (cont.)

• Next, use Newtons second law to calculate the
  acceleration.
• Finally, if necessary, use what you know about
  accelerated motion to find the velocity or
  position of the object.

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Force and Motion
SECTION4.1
Fighting Over a Toy
Anudja is holding a stuffed dog with a mass of
0.30 kg, when Sarah decides that she wants it and
tries to pull it away from Anudja. If Sarah pulls
horizontally on the dog with a force of 10.0 N
and Anudja pulls with a horizontal force of 11.0
N, what is the horizontal acceleration of the dog?
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Force and Motion
SECTION4.1
Fighting Over a Toy
Step 1 Analyze and Sketch the Problem

• Sketch the situation.
• Identify the stuffed dog as the system and the
  direction in which Anudja pulls as positive.
• Draw the free-body diagram. Label the force.

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Force and Motion
SECTION4.1
Fighting Over a Toy
Step 2 Solve for the Unknown
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Force and Motion
SECTION4.1
Fighting Over a Toy
Identify known and unknown variables.
Known m 0.30 kg FAnudja on dog 11.0 N
FSarah on dog 10.0 N
Unknown a ?
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Force and Motion
SECTION4.1
Fighting Over a Toy
Use Newtons second law to solve for a.
Fnet FAnudja on dog (-FSarah on dog)
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Force and Motion
SECTION4.1
Fighting Over a Toy
Substitute Fnet FAnudja on dog (FSarah on
dog)
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Force and Motion
SECTION4.1
Fighting Over a Toy
Substitute FAnudja on dog 11.0 N, FSarah on dog
10.0 N, m 0.30 kg
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Force and Motion
SECTION4.1
Fighting Over a Toy
Step 3 Evaluate the Answer
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Force and Motion
SECTION4.1
Fighting Over a Toy

• Are the units correct?
• m/s2 is the correct unit for acceleration.
• Does the sign make sense?
• The acceleration is in the positive direction
  because Anudja is pulling in the positive
  direction with a greater force than Sarah is
  pulling in the negative direction.

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Force and Motion
SECTION4.1
Fighting Over a Toy

• Is the magnitude realistic?
• It is a reasonable acceleration for a light,
  stuffed toy.

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Force and Motion
SECTION4.1
Fighting Over a Toy
The steps covered were

• Step 1 Analyze and Sketch the Problem
• Sketch the situation.
• Identify the stuffed dog as the system and the
  direction in which Anudja pulls as positive.
• Draw the free-body diagram. Label the forces.

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Force and Motion
SECTION4.1
Fighting Over a Toy
The steps covered were

• Step 2 Solve for the Unknown
• Step 3 Evaluate the Answer

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Force and Motion
SECTION4.1
Newtons First Law

• What is the motion of an object with no net force
  acting on it?
• Newtons second law states says that if net force
  is zero, then acceleration equal zero.
• If acceleration is zero, then velocity does not
  change.
• A stationary object with no net force acting on
  it will stay at rest.

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Force and Motion
SECTION4.1
Newtons First Law (cont.)

• What about a moving object like a rolling ball?
  How long will it roll?
• Depends on the surface thick carpet exerts more
  force than a smooth hard surface like a bowling
  alley.
• So the ball will stop rolling sooner on the
  carpet than the bowling alley.

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Force and Motion
SECTION4.1
Newtons First Law (cont.)

• Galileo did many experiments, and he concluded
  that in the ideal case of zero resistance,
  horizontal motion would never stop.
• Galileo was the first to recognize that the
  general principles of motion could be found by
  extrapolating experimental results to the ideal
  case, in which there is no resistance to slow
  down an objects motion.

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Force and Motion
SECTION4.1
Newtons First Law (cont.)

• In the absence of a net force, the motion (or
  lack of motion) of both the moving object and the
  stationary object continues as it was. Newton
  recognized this and generalized Galileos results
  in a single statement.
• This statement, an object that is at rest will
  remain at rest, and an object that is moving will
  continue to move in a straight line with constant
  speed, if and only if the net force acting on
  that object is zero, is called Newtons first
  law.

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Force and Motion
SECTION4.1
Newtons First Law (cont.)

• Newtons first law is sometimes called the law of
  inertia.
• Inertia is the tendency of an object to resist
  change.
• If an object is at rest, it tends to remain at
  rest.
• If it is moving at a constant velocity, it tends
  to continue moving at that velocity.
• Forces are results of interactions between two
  objects they are not properties of single
  objects, so inertia cannot be a force.

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Force and Motion
SECTION4.1
Newtons First Law (cont.)

• If the net force on an object is zero, then the
  object is in equilibrium.
• An object is in equilibrium if its velocity is
  not changing.
• Newtons first law identifies a net force as
  something that disturbs the state of equilibrium.
• Thus, if there is no net force acting on the
  object, then the object does not experience a
  change in speed or direction and is in
  equilibrium.

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Force and Motion
SECTION4.1
Newtons First Law (cont.)

• Some of the common types of forces are displayed
  on the right.
• When analyzing forces and motion, it is important
  to keep in mind that the world is dominated by
  resistance. Newtons ideal, resistance-free world
  is not easy to visualize.

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Section Check
SECTION4.1

• Two horses are pulling a 100-kg cart in the same
  direction, applying a force of 50 N each. What is
  the acceleration of the cart?

A. 2 m/s2 B. 1 m/s2 C. 0.5 m/s2 D. 0 m/s2
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Section Check
SECTION4.1
Answer
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Section Check
SECTION4.1

• Two friends Mary and Maria are trying to pull a
  10-kg chair in opposite directions. If Maria
  applied a force of 60 N and Mary applied a force
  of 40 N, in which direction will the chair move
  and with what acceleration?

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Section Check
SECTION4.1
A. The chair will move towards Mary with an
acceleration of 2 m/s2. B. The chair will move
towards Mary with an acceleration of 10 m/s2. C.
The chair will move towards Maria with an
acceleration of 2 m/s2. D. The chair will move
towards Maria with an acceleration of 10 m/s2.
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Section Check
SECTION4.1
Answer
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Section Check
SECTION4.1

• State Newtons first law.

Answer Newtons first law states that an object
that is at rest will remain at rest, and an
object that is moving will continue to move in a
straight line with constant speed, if and only if
the net force acting on that object is zero.
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Weight and Drag Force
SECTION4.2
MAIN IDEA Newtons second law can be used to
explain the motion of falling objects.
Essential Questions

• How are the weight and the mass of an object
  related?
• How do actual weight and apparent weight differ?
• What effect does air have on falling objects?

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Weight and Drag Force
SECTION4.2

• Review Vocabulary
• viscosity a fluids resistance to flowing.

• New Vocabulary
• Weight
• Gravitational pull
• Apparent weight

• Weightlessness
• Drag force
• Terminal velocity

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Weight and Drag Force
SECTION4.2
Weight

• Weight is the gravitational force experienced by
  an object.
• This gravitational force is a field force whose
  magnitude is directly proportional to the mass of
  the object experiencing the force
• Fg mg, where m is the mass of the object
  and g is the gravitational field.
• Because weight is a force, the proper unit used
  to measure weight is the newton.

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Weight and Drag Force
SECTION4.2
Weight (cont.)

• Gravitational field is a vector quantity that
  relates the mass of an object to the
  gravitational force it experiences at a given
  location.
• Near Earths surface, g is 9.8N/kg toward Earths
  center.

• When you step on a scale, the scale exerts an
  upward force on you equal in magnitude to the
  gravitational force pulling down on you.

• The scale is calibrated to convert the stretch of
  the springs, the upward force necessary to give a
  net force of zero, to weight .

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Weight and Drag Force
SECTION4.2
Weight (cont.)

• Apparent weight and weightlessness.

Click image to view movie.
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Weight and Drag Force
SECTION4.2
Drag Force

• When an object moves through any fluid, such as
  air or water, the fluid exerts a drag force on
  the moving object in the direction opposite to
  its motion.
• A drag force is the force exerted by a fluid on
  the object moving through the fluid.
• This force is dependent on the motion of the
  object, the properties of the object, and the
  properties of the fluid (viscosity and
  temperature) that the object is moving through.

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Weight and Drag Force
SECTION4.2
Drag Force (cont.)

• As a dropped tennis balls velocity increases, so
  does the drag force. The constant velocity that
  is reached when the drag force equals the force
  of gravity is called the terminal velocity.

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Weight and Drag Force
SECTION4.2
Drag Force (cont.)
Click image to view movie.
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Weight and Drag Force
SECTION4.2

• If the mass of a person on Earth is 20 kg, what
  will be his mass on the Moon? (Gravity on the
  Moon is six times less than the gravity on Earth.)

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Weight and Drag Force
SECTION4.2
Answer
Reason The mass of an object does not change
with the change in gravity, only the weight
changes.
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Weight and Drag Force
SECTION4.2

• Your mass is 100 kg, and you are standing on a
  bathroom scale in an elevator. What is the scale
  reading when the elevator is falling freely?

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Weight and Drag Force
SECTION4.2
Answer
Reason Since the elevator is falling freely with
acceleration g, the contact force between the
elevator and you is zero. As scale reading
displays the contact force, it would be zero.
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Weight and Drag Force
SECTION4.2

• In which of the following cases will your
  apparent weight be greater than your real weight?

A. The elevator is at rest. B. The elevator is
accelerating upward. C. The elevator is
accelerating downward. D. Apparent weight is
never greater than real weight.
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Weight and Drag Force
SECTION4.2
Answer
Reason When the elevator is moving upward, your
apparent weight
Fapparent ma Fg (where m is your mass and
a is the acceleration of the elevator). So your
apparent weight becomes more than your real
weight.
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Newtons Third Law
SECTION4.3
MAIN IDEA All forces occur in interaction pairs.
Essential Questions

• What is Newtons third law?
• What is the normal force?

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Newtons Third Law
SECTION4.3

• Review Vocabulary
• symmetry correspondence of parts on opposite
  sides of a dividing line.

• New Vocabulary
• Interaction pair
• Newtons third law
• Tension
• Normal force

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Newtons Third Law
SECTION4.3
Interaction Pairs

• When you exert a force on your friend to push him
  forward, he exerts an equal and opposite force on
  you, which causes you to move backward.

• The forces FA on B and FB on A are an interaction
  pair.
• An interaction pair is two forces that are in
  opposite directions and have equal magnitude.

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Newtons Third Law
SECTION4.3
Interaction Pairs (cont.)

• An interaction pair is also called an
  action-reaction pair of forces.
• This might suggest that one causes the other
  however, this is not true.
• For example, the force of you pushing your friend
  doesnt cause your friend to exert a force on
  you.
• The two forces either exist together or not at
  all.
• They both result from the contact between the two
  of you.

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Newtons Third Law
SECTION4.3
Interaction Pairs (cont.)

• The force of you on your friend is equal in
  magnitude and opposite in direction to the force
  of your friend on you.
• This is summarized in Newtons third law, which
  states that all forces come in pairs.

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Newtons Third Law
SECTION4.3
Interaction Pairs (cont.)

• Newtons Third Law states that the force of A on
  B is equal in magnitude and opposite in direction
  of the force of B on A.
• The two forces in a pair act on different objects
  and are equal and opposite.
• Numerically, FA on B FB on A

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Newtons Third Law
SECTION4.3
Interaction Pairs (cont.)

• When identifying an interaction pair, remember
  that they always occur in two different free-body
  diagrams and they always have the symmetry in
  subscripts noted on the previous slide.

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Newtons Third Law
SECTION4.3
Earths Acceleration
A softball has a mass of 0.18 kg. What is the
gravitational force on Earth due to the ball, and
what is Earths resulting acceleration? Earths
mass is 6.01024 kg.
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Newtons Third Law
SECTION4.3
Earths Acceleration (cont.)
Step 1 Analyze and Sketch the Problem

• Draw free-body diagrams for the two systems the
  ball and Earth.
• Connect the interaction pair by a dashed line.

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Newtons Third Law
SECTION4.3
Earths Acceleration (cont.)
Identify known and unknown variables.
Known mball 0.18 kg mEarth 6.01024 kg g
-9.80 m/s2
Unknown FEarth on ball ? aEarth ?
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Newtons Third Law
SECTION4.3
Earths Acceleration (cont.)
Step 2 Solve for the Unknown
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Newtons Third Law
SECTION4.3
Earths Acceleration (cont.)
Use Newtons second law to find the weight of the
ball.
FEarth on ball mballg
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Newtons Third Law
SECTION4.3
Earths Acceleration (cont.)
Substitute mball 0.18 kg, g -9.80 m/s2
FEarth on ball (0.18 kg)(-9.80 m/s2)
-1.8 N
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Newtons Third Law
SECTION4.3
Earths Acceleration (cont.)
Use Newtons third law to solve for Fball on
Earth.
Fball on Earth FEarth on ball
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Newtons Third Law
SECTION4.3
Earths Acceleration (cont.)
Substitute FEarth on ball 1.8 N
Fball on Earth ( 1.8 N) 1.8N
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Newtons Third Law
SECTION4.3
Earths Acceleration (cont.)
Use Newtons second and third laws to find aEarth.
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Newtons Third Law
SECTION4.3
Earths Acceleration (cont.)
Substitute Fnet 1.8 N, mEarth 6.01024 kg
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Newtons Third Law
SECTION4.3
Earths Acceleration (cont.)
Step 3 Evaluate the Answer
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Newtons Third Law
SECTION4.3
Earths Acceleration (cont.)

• Are the units correct?
• Dimensional analysis verifies force in N and
  acceleration in m/s2.
• Does the sign make sense?
• Force and acceleration should be positive.

88
Newtons Third Law
SECTION4.3
Earths Acceleration (cont.)

• Is the magnitude realistic?
• Because of Earths large mass, the acceleration
  should be small.

89
Newtons Third Law
SECTION4.3
Earths Acceleration (cont.)
The steps covered were

• Step 1 Analyze and Sketch the Problem
• Draw free-body diagrams for the two systems the
  ball and Earth.
• Connect the interaction pair by a dashed line.
• Step 2 Solve for the Unknown
• Step 3 Evaluate the Answer

90
Newtons Third Law
SECTION4.3
Tension

• The force exerted by a string or rope is called
  tension.
• At any point in a rope, the tension forces are
  pulling equally in both directions.

91
Newtons Third Law
SECTION4.3
Tension (cont.)
92
Newtons Third Law
SECTION4.3
The Normal Force

• The normal force is the perpendicular contact
  force exerted by a surface on another object.
• The normal force is important when calculating
  resistance.

93
Section Check
SECTION4.3

• Explain Newtons third law.

94
Section Check
SECTION4.3
Answer

• Answer Suppose you push your friend. The force
  of you on your friend is equal in magnitude and
  opposite in direction to the force of your friend
  on you. This is summarized in Newtons third law,
  which states that forces come in pairs. The two
  forces in a pair act on different objects and are
  equal in strength and opposite in direction.
• Newtons third law FA on B FB on A
• The force of A on B is equal in magnitude and
  opposite in direction of the force of B on A.

95
Section Check
SECTION4.3

• If a stone is hung from a rope with no mass, at
  which place on the rope will there be the most
  tension?

A. The top of the rope, near the hook. B. The
bottom of the rope, near the stone. C. The
middle of the rope. D. The tension will be the
same throughout the rope.
96
Section Check
SECTION4.3
Answer
Reason Because the rope is assumed to be without
mass, the tension everywhere in the rope is equal
to the stones weight.
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98
Forces in One Dimension
CHAPTER4
Resources
Physics Online Study Guide Chapter Assessment
Questions Standardized Test Practice
99
Force and Motion
SECTION4.1
Study Guide

• A force is a push or a pull. Forces have both
  direction and magnitude. A force might be either
  a contact force or a field force.
• Newtons second law states that the acceleration
  of a system equals the net force acting on it
  divided by its mass.

100
Force and Motion
SECTION4.1
Study Guide

• Newtons first law states that an object that is
  at rest will remains at rest and an object that
  is moving will continue to move in a straight
  line with constant speed, if and only if the net
  force acting on that object is zero. An object
  with zero net force acting on it is in
  equilibrium.

101
Weight and Drag Force
SECTION4.2
Study Guide

• The objects weight (Fg) depends on the objects
  mass and the gravitational field at the objects
  location.
• An objects apparent weight is the magnitude of
  the support force exerted on it. An object with
  no apparent weight experiences weightlessness.

102
Weight and Drag Force
SECTION4.2
Study Guide

• A falling object reaches a constant velocity when
  the drag force is equal to the objects weight.
  The constant velocity is called the terminal
  velocity. The drag force on an object is
  determined by the objects weight, size and shape
  as well as the fluid through which it moves.

103
Newtons Third Law
SECTION4.3
Study Guide

• Newtons third law states that the two forces
  that make up an interaction pair of forces are
  equal in magnitude, but opposite in direction and
  act on different objects. In an interaction
  pair, FA on B does not cause FB on A. The two
  forces either exist together or not at all.

104
Newtons Third Law
SECTION4.3
Study Guide

• The normal force is a support force resulting
  from the contact between two objects. It is
  always perpendicular to the plane of contact
  between the two objects.

105
Forces in One Dimension
CHAPTER4
Chapter Assessment
Combining Forces

• If you and your friend exert a force of 100 N
  each on a table, first in the same direction and
  then in opposite directions, what is the net
  force?

106
Forces in One Dimension
CHAPTER4
Chapter Assessment
Combining Forces

• In the first case, your friend is pushing with a
  negative force of 100 N. Adding them together
  gives a total force of 0 N.

107
Forces in One Dimension
CHAPTER4
Chapter Assessment
Combining Forces

• In the second case, your friends force is 100 N,
  so the total force is 200 N in the positive
  direction and the table accelerates in the
  positive direction.

108
Forces in One Dimension
CHAPTER4
Chapter Assessment
Newtons Second Law

• Newtons second law can be rearranged to the form
  F ma, which you
  learned about previously.
• Assume that the table that you and your friend
  were pushing was 15.0 kg and the two of you each
  pushed with a force of 50.0 N in the same
  direction.
• To find out what the acceleration of the table
  would be, calculate the net force, 50.0 N 50.0
  N 100.0 N, and apply Newtons second law by
  dividing the net force of 100.0 N by the mass of
  the table, 15.0 kg, to get an acceleration of
  6.67 m/s2.

109
Forces in One Dimension
CHAPTER4
Chapter Assessment
Forces of Ropes and Strings

• Tension forces are at work in a tug-of-war.
• If team A, on the left, is exerting a force of
  500 N and the rope does not move, then team B,
  must also be pulling with 500 N.

Tim Fuller
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Fighting Over a Toy
Anudja is holding a stuffed dog, with a mass of
0.30 kg, when Sarah decides that she wants it and
tries to pull it away from Anudja. If Sarah pulls
horizontally on the dog with a force of 10.0 N
and Anudja pulls with a horizontal force of 11.0
N, what is the horizontal acceleration of the dog?
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Earths Acceleration
When a softball with a mass of 0.18 kg is
dropped, its acceleration toward Earth is equal
to g, the acceleration due to gravity. What is
the force on Earth due to the ball, and what is
Earths resulting acceleration? Earths mass is
6.01024 kg.
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• If a golf ball, baseball and bowling ball are
  thrown with the same force, which ball will move
  with a greater acceleration?

A. Golf ball B. Baseball C. Bowling ball D.
The three balls will have equal acceleration.
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• Jack is boating in a river applying a contact
  force of 30 N, in a direction opposite to the
  flow of water. At the same time, the water is
  exerting a force of 30 N on the boat. In which
  direction will the boat move?

A. The boat will move in the direction of the
flow of water. B. The boat will not move at
all. C. The boat will move back and forth within
a particular distance. D. The boat will move in
the direction opposite to the flow of water.
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Reason Since two equal and opposite forces are
acting together, the net force is zero. Hence,
the boat will not move at all.
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Chapter Assessment

• What is inertia?

A. Force. B. The tendency of a body to stay
only at rest C. The tendency of a body to move
with constant acceleration D. The tendency of a
body to move with constant velocity
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Chapter Assessment

• Reason Inertia of a body is the tendency of a
  body to stay at rest and/or to move with a
  constant velocity. Remember being at rest is
  simply a special case of constant velocity, v 0
  m/s.

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• If the weight of a person on Earth is 120 N, what
  will his weight be on the Moon? (Gravity on the
  Moon is six times less than the gravity on Earth.)

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Reason Gravity on the Moon is .
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Chapter Assessment
Reason
Weight of person on the Moon
Gravity on the Moon
mass of person
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Chapter Assessment

• What happens when the drag force is equal to the
  force of gravity?

A. The object comes to rest. B. The object
moves with constant acceleration. C. The object
moves with constant velocity. D. The velocity of
the object increases.
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Reason When drag force equals the force due to
gravity, the net force acting on the object is
zero. As a result of this, the object moves with
constant velocity, which is called terminal
velocity.
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Standardized Test Practice

• What is the acceleration of the car described by
  the graph on the right?

A. 0.20 m/s2 B. 0.40 m/s2
C. 1.0 m/s2 D. 2.5 m/s2
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Standardized Test Practice

• What distance will the car described by the above
  graph have traveled after 4.0 s?

A. 13 m B. 40 m
C. 80 m D. 90 m
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Standardized Test Practice

• If the car in the graph on the right maintains a
  constant acceleration, what will its velocity be
  after 10 s.

A. 10 km/h B. 25 km/h
C. 90 km/h D. 120 km/h
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Standardized Test Practice

• In a tug-of-war, 13 children, with an average
  mass of 30 kg each, pull westward on a rope with
  an average force of 150 N per child. Five
  parents, with an average mass of 60 kg each, pull
  eastward on the other end of the rope with an
  average force of 475 N per adult. Assuming that
  the whole mass accelerates together as a single
  entity, what is the acceleration of the system?

A. 0.62 m/s2 E B. 2.8 m/s2 W
C. 3.4 m/s2 E D. 6.3 m/s2 W
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Standardized Test Practice

• What is the weight of a 225-kg space probe on the
  Moon? The acceleration of gravity on the Moon is
  1.62 m/s2.

A. 139 N B. 364 N C. 1.35103 N D. 2.21103 N
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Standardized Test Practice
Test-Taking Tip

• Maximize Your Score

If possible, find out how your standardized test
will be scored. In order to do your best, you
need to know if there is a penalty for guessing,
and if so, what the penalty is. If there is no
random-guessing penalty at all, you should always
fill in an answer, even if you have not read the
question.
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Chapter Resources
Forces Exerted on the Book
130
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Chapter Resources
Ball Tied to a String
131
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Ball Held in Your Hand
132
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The Carts Motion Shown in a Linear Relationship
133
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Acceleration of Cart
134
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Force-Acceleration Graph
135
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Combining Forces
136
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Chapter Resources
Fighting Over a Toy
137
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Chapter Resources
An Elevator Accelerating Upward
138
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Chapter Resources
A Soccer Ball on a Table on Earth
139
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Chapter Resources
Earths Acceleration
140
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Chapter Resources
The Normal Force on an Object
141
End of Custom Shows