Download Section 2 What Is a Force?

Chapter 12
Matter in Motion
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Section 1 Measuring Motion
Section 2 What Is a Force?
Section 3 Friction: A Force That Opposes Motion
Concept Map
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Chapter 12
Section 2 What Is a Force?
Quick Write
A force is a push or a pull on an object. Imagine that
you are trying to push a box up a ramp. Describe as
many forces (pushes and pulls) as you can in that
situation. Be sure to include the direction of each
force (push or pull) in your description.
Write your answers in your Notebook.
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Chapter 12
Section 2 What Is a Force?
What You Will Learn
CA Standard
What It Means
8.2.a Students know a A force acts in a
force has both direction particular direction and
and magnitude.
has a certain size.
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Why It Matters
Knowing the size and
direction of a force
helps one predict the
effect of the force on an
object.
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Chapter 12
Section 2 What Is a Force?
Key Concept
Key Concept
Forces acting on an object can be
combined and may cause changes
in motion.
Why It Matters
You exert forces to move objects
around you.
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Chapter 12
Section 2 What Is a Force?
Forces Acting on Objects
• A force is a push or a pull exerted on an object in
order to change the motion of the object.
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Chapter 12
Section 2 What Is a Force?
Forces Acting on Objects
• All forces have two properties: direction and
magnitude (size).
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Chapter 12
Section 2 What Is a Force?
Forces Acting on Objects
• Forces can cause acceleration.
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Chapter 12
Section 2 What Is a Force?
Forces Acting On Objects
• newton (N) = SI unit used to describe the magnitude
(size) of a force.
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Chapter 12
Section 2 What Is a Force?
Forces Acting on Objects
• A force can act on
an object without
causing the object to
move.
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Chapter 12
Section 2 What Is a Force?
Demonstration: Changing Weight
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Chapter 12
Section 2 What Is a Force?
Combined Effect of Forces
• net force = all the forces acting on an object
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Chapter 12
Section 2 What Is a Force?
Activity: Finding Net Force
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Chapter 12
Section 2 What Is a Force?
Combined Effect of Forces
• forces in the same direction:
 net force = force + force
ex:
36 N
15 N
36 + 15 = 41N to the right
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Chapter 12
Section 2 What Is a Force?
Combined Effect of Forces
1.
=
21 N
105 N
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Chapter 12
Section 2 What Is a Force?
Combined Effect of Forces
1.
=
21 N
105 N
105 + 21 = 126 N to the right
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Chapter 12
Section 2 What Is a Force?
Combined Effect of Forces
2.
49 N
=
78 N
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Chapter 12
Section 2 What Is a Force?
Combined Effect of Forces
2.
49 N
=
78 N
49 + 78 = 127 N to the left
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Chapter 12
Section 2 What Is a Force?
Combined Effect of Forces
• forces act in opposite directions:
 net force = force – force
ex:
16 N
45 N
45 – 16 = 29 N to the right
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Chapter 12
Section 2 What Is a Force?
Combined Effect of Forces
1.
10 N
=
37 N
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Main
Chapter 12
Section 2 What Is a Force?
Combined Effect of Forces
1.
10 N
=
37 N
37 – 10 = 27 N to the right
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Chapter 12
Section 2 What Is a Force?
Combined Effect of Forces
2.
96 N
=
25 N
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Chapter 12
Section 2 What Is a Force?
Combined Effect of Forces
2.
96 N
=
25 N
96 – 25 = 71 N to the left
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Chapter 12
Matter in Motion
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Chapter 12
Section 2 What Is a Force?
Balanced Forces: No Change in Motion
• net force = 0 N → balanced forces
• no change in the motion of an object
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Chapter 12
Section 2 What Is a Force?
Balanced Forces: No Change in Motion
• not moving +
balanced forces =
static
• ex:
– compression =
pushed or
squeezed
– tension = pulled
or stretched
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Chapter 12
Section 2 What Is a Force?
Unbalanced Forces: Velocity Changes
• net force ≠ 0 N → unbalanced forces
• cause a change in the velocity of an object
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Chapter 12
Section 2 What Is a Force?
Unbalanced Forces: Velocity Changes
• needed to cause static
objects to start moving
• Objects do not always move
in the direction of the
unbalanced force.
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Chapter 12
Section 2 What Is a Force?
Project: Identifying Forces
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