This document provides an overview of Chapter 5 from a physics textbook. It covers Newton's three laws of motion: 1) inertia and an object's resistance to changes in motion, 2) the relationship between force, mass and acceleration, and 3) that for every action there is an equal and opposite reaction. Key topics discussed include force, inertia, equilibrium, calculating acceleration and force using Newton's second law, and identifying action-reaction force pairs per Newton's third law. Locomotion and biomechanics are also mentioned in relation to applying Newtonian mechanics to human and animal movement.

2. Chapter5: Newton’s Laws:
Force and Motion
 5.1 The First Law: Force and Inertia
 5.2 The Second Law: Force, Mass and
Acceleration
 5.3 The Third Law: Action and Reaction

3. Chapter5 Objectives
 Describe how the law of inertia affects the motion of an object.
 Give an example of a system or invention designed to overcome
inertia.
 Measure and describe force in newtons (N) and pounds (lb).
 Calculate the net force for two or more forces acting along the same
line.
 Calculate the acceleration of an object from the net force acting on it.
 Determine whether an object is in equilibrium by analyzing the forces
acting on it.
 Draw a diagram showing an action-reaction pair of forces.
 Determine the reaction force when given an action force.

4. Chapter5 Vocabulary
 action
 dynamics
 equilibrium
 force
 law of inertia
 locomotion
 net force
 newton (N)
 Newton’s first law
 Newton’s second law
 Newton’s third law
 reaction
 statics

5. 5.1 The First Law: Force and Inertia
Investigation Key Question:
How does the first law apply to objects
at rest and in motion?

6. 5.1 Force
 Force is an action that can change motion.
 A force is what we call a push ora pull, orany
action that has the ability to change an object’s
motion.
 Forces can be used to increase the speed of an
object, decrease the speed of an object, orchange
the direction in which an object is moving.

8. 5.1 Inertia
 Inertia is a termused to measure the ability of an
object to resist a change in its state of motion.
 An object with a lot of inertia takes a lot of force to
start orstop; an object with a small amount of inertia
requires a small amount of force to start orstop.
 The word “inertia” comes fromthe Latin word inertus,
which can be translated to mean “lazy.”

9. 5.1 Newton's First Law
 Can you explain why the long table would make
the trickhard to do?

10.  The engine
 supplies force that allows you to change motion by pressing the
gas pedal.
 The brake system
 is designed to help you change yourmotion by slowing down.
 The steering wheel and steering system
 is designed to help you change yourmotion by changing your
direction.
How do these systems in a carovercome
the law of inertia?

11. 5.2 The Second Law:
Force, Mass, and Acceleration
Investigation Key Question:
 What is the relationship between
force, mass, and acceleration?

12. 5.2 Newton's Second Law
 If you apply
more force to
an object, it
accelerates at
a higherrate.

13. 5.2 Newton's Second Law
 If the same force is
applied to an object
with greatermass,
the object
accelerates at a
slowerrate because
mass adds inertia.

15. 5.2 The definition of force
 The simplest concept of force is a push ora
pull.
 On a deeperlevel, force is the actionthat has
the ability to create orchange motion.

16. 5.2 The definition of force
 In the English system,
the unit of force, the
pound, was originally
defined by gravity.
 The metric definition
of force depends on
the acceleration per
unit of mass.

17. 5.2 Newton's Second Law
 A force of one newton is exactly the amount
of force needed to cause a mass of one
kilogramto accelerate at one m/s2.
 We call the unit of force the newton (N).

18. 5.2 Newton's Second Law
a = F
m
Force (newtons, N)
Mass (kg)
Acceleration (m/sec2
)

19. 5.2 Using the second law of motion
 The force Fthat appears in the second law is the net
force.
 There are often many forces acting on the same
object.
 Acceleration results fromthe combined action of
all the forces that act on an object.
 When used this way, the word net means “total.”

20. 5.2 Converting newtons and pounds
 A force of one pound is equal to about 4.448
newtons.

21. 5.2 Using the second law of motion
 To solve problems with multiple forces, you
have to add up all the forces to get a single
net force before you can calculate any
resulting acceleration.

22. 1. You are asked for the acceleration (a).
2. You are given mass (m ) and force (F).
3. Newton’s second law applies: a = F ÷ m
4. Plug in numbers. (Remember: 1 N = 1 kg·m/s2
)
Calculating acceleration
A cart rolls down a ramp. Using a
spring scale, you measure a net
force of 2 newtons pulling the car
down. The cart has a mass of 500
grams (0.5 kg). Calculate the
acceleration of the cart.

23. 5.2 Newton's Second Law
Three forms of the second law:

24. 5.2 Finding the acceleration
of moving objects
 The word dynamics refers to problems
involving motion.
 In dynamics problems, the second law is
often used to calculate the acceleration of an
object when you know the force and mass.

25. 5.2 Direction of acceleration
 Speed increases when
the net force is in the
same direction as the
motion.
 Speed decreases when
the net force is in the
opposite direction as
the motion.

26. 5.2 Positive and negative acceleration
 We often use positive and negative numbers to
show the direction of force and acceleration.
 A common choice is to make velocity, force, and
acceleration positive when they point to the right.

27. 1. You are asked for the acceleration (a) and direction
2. You are given the forces (F) and mass (m ).
3. The second law relates acceleration to force and mass: a = F ÷ m
4. Assign positive and negative directions. Calculate the net force then
use the second law to determine the acceleration from the net force
and the mass.
Acceleration frommultiple forces
Three people are pulling on a wagon
applying forces of 100 N, 150 N, and
200 N. Determine the acceleration
and the direction the wagon moves.
The wagon has a mass of 25
kilograms.

28. 5.2 Finding force from acceleration
 Whereverthere is acceleration there must
also be force.
 Any change in the motion of an object
results fromacceleration.
 Therefore, any change in motion must be
caused by force.

29. 1. You asked for the force (F).
2. You are given the mass (m ) and acceleration (a).
3. The second law applies: a = F ÷ m
4. Plug in the numbers. Remember: 1 N = 1 kg·m/s2
.
Calculating force
An airplane needs to accelerate at 5
m/sec2
to reach take-off speed before
reaching the end of the runway. The mass
of the airplane is 5,000 kilograms. How
much force is needed fromthe engine?

30. Calculating force
A tennis ball contacts the racquet formuch less
than one second. High-speed photographs
show that the speed of the ball changes from
-30 to +30 m/sec in 0.006 seconds. If the mass
of the ball is 0.2 kg, how much force is applied
by the racquet?

31. 5.2 Equilibrium
 The condition of zero acceleration is called
equilibrium.
 In equilibrium, all forces cancel out leaving
zero net force.
 Objects that are standing still are in
equilibriumbecause theiracceleration is
zero.

32. 5.2 Equilibrium
 Objects that are moving at
constant speed and direction
are also in equilibrium.
 A static problemusually
means there is no motion.

33. 1. You are asked for force (F).
2. You are given two 80 N forces and the fact that the dogs
are not moving (a = 0).
3. Newton’s second law says the net force must be zero if
the acceleration is zero.
4. The woman must exert a force equal and opposite to the
sum of the forces from the two dogs.
Calculating force
A woman is holding two dogs on a leash. If
each dog pulls with a force of 80 newtons,
how much force does the woman have to
exert to keep the dogs frommoving?

34. 5.3 The Third Law: Action and
Reaction
Investigation Key Question:
Can you identify action-reaction forces?

35. 5.3 The Third Law: Action and Reaction
 “Forevery action there is an
equal and opposite reaction.”
 This statement is known as
Newton’s third law of motion.
 Newton’s third law discusses
pairs of objects and the
interactions between them.

36. 5.3 Forces occurin pairs
 The astronauts working on the space station have a serious
problemwhen they need to move around in space: There is
nothing to push on.
 One solution is to throw something opposite the direction
you want to move.

37. 5.3 Forces occurin pairs
 The two forces in a pairare
called actionand reaction.
 Anytime you have one, you
also have the other.
 If you know the strength of
one you also know the
strength of the othersince
both forces are always equal.

38. 5.3 Newton's Third Law
 Newton’s thirdlaw states that
forevery action force there
has to be a reaction force
that is equal in strength and
opposite in direction.
 Action and reaction forces
act on different objects, not
on the same object.

39. 5.3 Newton's Third Law
 Newton’s thirdlaw states that forevery action force
there has to be a reaction force that is equal in
strength and opposite in direction.
 Action and reaction forces act on different objects,
not on the same object.
 The forces cannot cancel because they act on
different objects.

40. Calculating force
Three people are each applying 250 newtons of force to
try to move a heavy cart. The people are standing on a
rug. Someone nearby notices that the rug is slipping. How
much force must be applied to the rug to keep it from
slipping? Sketch the action and reaction forces acting
between the people and the cart and between the people
and the rug.

41. 5.3 Locomotion
 The act of moving orthe ability to move fromone
place to anotheris called locomotion.
 Any animal ormachine that moves depends on
Newton’s third law to get around.
 When we walk, we push off the ground and move
forward because of the ground pushing backon us
in the opposite direction.

42. 5.3 Locomotion
 Jets, planes, and
helicopters push air.
 In a helicopter, the
blades of the propeller
are angled such that
when they spin, they
push the airmolecules
down.

44.  Biomechanics is the science of how physics is applied to
muscles and motion.
 Many athletes use principles of biomechanics to improve
their performance.
 People who design sports equipment use biomechanics to
achieve the best performance by matching the equipment
design to the athlete’s body.
 Physicians, carpenters, people who build furniture, and
many others also use biomechanics in their work.
 Any machine that relies on forces from the human body also
relies on biomechanics.
BIOMECHANICS