Forces and Newton’s
Laws of Motion
1. “What is a force?”
2. “Do objects need to touch to
experience a force?”
Forces and Newton’s Laws of Motion
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Forces and Diagrams
What We Want to Know
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What is force, and what types of forces are
there?
What is the difference between mass and
weight?
What are the advantages of drawing freebody diagrams when analyzing forces?
A Little History…
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Aristotle a famous Greek philosopher around
400 BC
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Natural Motion…
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Violent Motion…
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objects seek their natural resting places
Not caused by force
Result of forces that push or pull an object
External cause… moving against nature
No force… No motion
Do you agree?
A Little History…
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Galileo the foremost scientist of the lateRenaissance
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Asked how things moved rather than why
Demolished the notion that force is necessary to
keep an object moving
Only when friction is present is force required to
keep objects moving
Without frictional force, an object’s motion will
continue
Open the door for Isaac Newton and his Laws of
Motion
Describe the ball

The ball’s motion will not change on its own.
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Something must cause an objects motion to
change.
Force

Force: a push or pull on an object which may
change an objects state of rest or motion.
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Forces cause a change in an object’s speed
and/or direction.
Forces cause acceleration.
Forces are measured in Newtons (N).
Forces only exist as a result of objects interacting.
If their interaction stops, then there is no force.
Force

The forces that result from the interactions
can be generalized as either contact forces or
field forces.
Contact Forces

Contact Forces: forces resulting from actual
physical contact between objects.
Field Forces

Field Forces: forces that are exerted from an
interaction between objects, despite not
being in physical contact with one another.
Examples
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Contact Forces
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Applied Forces
Tension Forces
Spring Forces
Frictional Forces
Normal Force
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Field Forces
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Gravitational Forces
Magnetic Forces
Electrical Forces
Weight vs. Mass

Weight is the force of gravity acting on an
object.
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The value of weight varies depending on where
you are. ie. Earth, the Moon, another planet, etc.
Weight = mass x gravity (W = mg)
Mass is the amount of matter in an object.
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The value of an objects mass is the same
everywhere and does not change on location.
Normal Force

Normal Force: Results from contact with a
surface.
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The force that acts perpendicular to the
surface.
Vectors
Force (F)
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Forces are vectors
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Have a magnitude and
direction.
Can be added or
subtracted to form a
resultant.
Can be resolved into
components.
Force and free-body
diagrams can help
analyze forces at work.
Vertical
Component
q
Horizontal
Component
Fx  F cos q
Fy  F sin q
Force and Free-body Diagrams
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Force diagrams: shows all interacting objects and forces.
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Free-body diagrams: help analyze situations by isolating a single
object and the forces that are acting on that object.
Example Diagram
Practice
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Draw a free-body diagram for:
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A book sitting on a table.
A person starts a cart rolling down a ramp.
The cart rolling down a ramp.
A box at rest on a ramp.
A person pulling a sled across a frozen lake.
A bus being pushed over rocky terrain.
Objectives
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What is force, and what types of forces are
there?
What is the difference between mass and
weight?
What are the advantages of drawing freebody diagrams when analyzing forces?
Exit Ticket

Reflect on your answers to “What is a force?”
and “Do objects need to touch to experience
a force?”
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Are your answers different now than they were
before?
Why did you think that way?