Forces
Types of Forces
Effects of Forces
Gravity, Mass and Weight
Newton’s Laws
Freefall
What is force?
Common symbol: F
Unit: Newton, N
Equivalent base units: kg-m-s-2
Types of Forces
 Contact Force
 Push
 Pull
 Friction
 Tension
 Normal Force
 Upthrust
 Bouyancy
 Lift
 Drag
 Resistance
 Thrust
 Engine
 Non-contact Force
 Gravitational Force
 Weight
 Electrical Force
 Magnetic Force
Types of Forces: Contact Force
Tension
pull
Friction
Normal Force
Types of Forces: Contact Force
Upthrust
Drag
Types of Forces: Contact Force
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Thrust
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Thrust
Types of Forces: Contact Forces
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Thrust
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Lift
Types of Forces: Non-Contact Forces
Weight
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Thrust
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Weight
Types of Forces: Non-Contact Forces
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Electrical Force
Magnetic Force
Mass versus Weight
 Mass
Amount of matter in an
object
unit: kilogram, kg
Does not change with
location
 Weight
Gravitational force on
the object
Unit: Newton, N
Equal to
 Mass x acceleration
due to gravity
m x g
 Where g = 10 ms-2
Changes with location
On earth, always acting
downward
Weight
Normal force
Weight
Air resistance
Weight
Drag
Friction
Thrust
Normal Force
Weight
Drag
Thrust
Upthrust
Effects of Forces
Change shape
Rigid bodies
Change the state of motion
Move from rest
Speed up
Slow down
Stop
Change its direction
Newton’s Laws
Change of Shape
extension
Who is Isaac Newton?
“Nature and Nature's laws lay hid in night:
God said, Let Newton be! and all was
light.”
Newton’s Third Law
For every action
there is an equal
and opposite
reaction
Law of Action and Reaction
Action and Reaction Forces
Action and Reaction Forces
Newton’s First Law
If no unbalanced
force acts on a
body then the
body is in
equilibrium.
Law of Inertia
What is Inertia?
The tendency of a body to resist changes in
its state of motion.
It is measured in terms of mass of a body.
When the forces are balanced
The body does not move,or
The body moves
At a constant speed
In the same direction
Balanced forces
Balanced Forces
The book stays still!
Balanced Forces
The airplane moves forwards at constant speed!
Balanced Forces
Drag
Thrust
Friction
The car moves at constant speed!
Your Turn!
Question #1, page 104
Newton’s Second Law
 An unbalanced force changes the motion
of an object.
It speeds up
Or slows down
Or changes direction
Or changes speed and direction
 Acceleration
change in motion
 Equation
a =
force
mass
Unbalanced Forces
The car moves from rest.
The car speeds up.
Unbalanced Forces
The car slows down to stop.
The car slows down.
The Physics of Falling
The Physics of Falling
 Freefall
Motion where only gravity is acting on the body
Air resistance is negligible
As the body falls, its
Speed increases
Acceleration is constant
Acceleration = g
The Physics of Skydiving
The Physics of Falling with Air Resistance
Air resistance increases with speed
Terminal Velocity
The maximum speed of a falling object
When upward forces balance downward forces
on the object
The End