Forces

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Forces

• Types of Forces
• Effects of Forces
• Gravity, Mass and Weight
• Newtons Laws
• Freefall

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What is force?
Common symbol F Unit Newton, N Equivalent base
units kg-m-s-2
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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

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Types of Forces Contact Force
Tension
Friction
pull
Normal Force
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Types of Forces Contact Force
Upthrust
Drag
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Types of Forces Contact Force
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Thrust
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Thrust
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Types of Forces Contact Forces
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Thrust
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Lift
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Types of Forces Non-Contact Forces
Weight
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Thrust
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Weight
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Types of Forces Non-Contact Forces
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Electrical Force
Magnetic Force
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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

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Weight
Weight
Normal force
Air resistance
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Weight
Thrust
Drag
Friction
Normal Force
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Weight
Thrust
Drag
Upthrust
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Effects of Forces

• Change shape
• Rigid bodies
• Change the state of motion
• Move from rest
• Speed up
• Slow down
• Stop
• Change its direction
• Newtons Laws

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Change of Shape
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extension
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Who is Isaac Newton?
Nature and Nature's laws lay hid in nightGod
said, Let Newton be! and all was light.
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Newtons Third Law
For every action there is an equal and opposite
reaction
Law of Action and Reaction
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Action and Reaction Forces
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Action and Reaction Forces
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Newtons First Law
If no unbalanced force acts on a body then the
body is in equilibrium.
Law of Inertia
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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.

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When the forces are balanced

• The body does not move,or
• The body moves
• At a constant speed
• In the same direction

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Balanced forces
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Balanced Forces
The book stays still!
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Balanced Forces
The airplane moves forwards at constant speed!
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Balanced Forces
Thrust
Drag
Friction
The car moves at constant speed!
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Your Turn!

• Question 1, page 104

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Newtons 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
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Unbalanced Forces
The car moves from rest.
The car speeds up.
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Unbalanced Forces
The car slows down to stop.
The car slows down.
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The Physics of Falling
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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

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The Physics of Skydiving
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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

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The End