Motion & Forces
Speed & Velocity
• Speed - the rate of change in
position over time (distance/time)
• Instantaneous speed
• Average speed
...
Change in Velocity

What makes an object
change velocity?
Force
• Push or Pull
• Forces can cause a change
in velocity
• Examples:
Gravity
Magnetism
Friction
Balanced Forces
Forces that
– act on the same object
– are opposite in direction
– are equal in size
Balanced Forces
Book on table
1. Weight of the book
is downward force
caused by gravity
2. Table pushes back
with an equal...
Unbalanced Forces
Forces that are NOT opposite
and equal
What do they cause?

CHANGE IN VELOCITY
ACCELERATION
Friction
Force that opposes
motion between 2
surfaces
Depends on the:
• types of surfaces
• force between the
surfaces
Types of Friction
• Static Friction:

(Couch Potato)

– Force between objects at rest

• Sliding Friction:

(Ice skating)
...
Friction
Friction is greater...
–between rough
surfaces
–when there’s greater
force between surfaces
(such as more weight)
Lubricant
Changes sliding friction
into fluid friction
Friction
Is friction always bad?
Gravity
The attractive force
between all objects
in the universe
Acceleration of
Gravity
Near the surface of the earth the
acceleration due to gravity is 9.8
m/s/s
Newton’s 1 Law
st

An object at rest remains at
rest and an object in motion
will continue moving at a
constant velocity u...
Newton’s Laws of
Motion
Newton’s 1 Law
st

INERTIA
• tendency of an object to resist
any change in its motion
• increases as mass increases
Newton‘s 2

nd

Law

If more force is applied, an
object will be accelerated _____
more
Newton’s 2

nd

Law

• More force means more
acceleration
• More mass means less
acceleration
Force = mass X acceleration
...
Newton’s 3

rd

Law

For every action, there is an equal
and opposite reaction.
Forces occur only in pairs
– Act on differ...
Newton’s 3

rd

Law

The hammer
exerts a force on
the nail to the
right.
The nail exerts an
equal but opposite
force on th...
Momentum
Terminal Velocity

The final speed of a
falling object.
Terminal Velocity
Air resistance is
offsetting the the
weight of the
object
Forces
End
Force
Aristotle's idea:
For an object to move at a
constant speed, a constant
force must be applied.
Force
Newton’s idea:
An object moving at a constant speed
will continue at that speed without
additional force being appli...
Balanced Forces
Force and motion
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Force and motion

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Force and motion

  1. 1. Motion & Forces
  2. 2. Speed & Velocity • Speed - the rate of change in position over time (distance/time) • Instantaneous speed • Average speed • How is velocity different from speed? Velocity describes both speed and direction
  3. 3. Change in Velocity What makes an object change velocity?
  4. 4. Force • Push or Pull • Forces can cause a change in velocity • Examples: Gravity Magnetism Friction
  5. 5. Balanced Forces Forces that – act on the same object – are opposite in direction – are equal in size
  6. 6. Balanced Forces Book on table 1. Weight of the book is downward force caused by gravity 2. Table pushes back with an equal and opposite force Net force is zero
  7. 7. Unbalanced Forces Forces that are NOT opposite and equal What do they cause? CHANGE IN VELOCITY ACCELERATION
  8. 8. Friction Force that opposes motion between 2 surfaces Depends on the: • types of surfaces • force between the surfaces
  9. 9. Types of Friction • Static Friction: (Couch Potato) – Force between objects at rest • Sliding Friction: (Ice skating) – Solid surfaces slide over each other • Rolling Friction: (Rollerblading) – An object rolls over a surface. • Fluid friction: (Submarine) – An object moves through a fluid
  10. 10. Friction Friction is greater... –between rough surfaces –when there’s greater force between surfaces (such as more weight)
  11. 11. Lubricant Changes sliding friction into fluid friction
  12. 12. Friction Is friction always bad?
  13. 13. Gravity The attractive force between all objects in the universe
  14. 14. Acceleration of Gravity Near the surface of the earth the acceleration due to gravity is 9.8 m/s/s
  15. 15. Newton’s 1 Law st An object at rest remains at rest and an object in motion will continue moving at a constant velocity unless acted on by unbalanced forces.
  16. 16. Newton’s Laws of Motion
  17. 17. Newton’s 1 Law st INERTIA • tendency of an object to resist any change in its motion • increases as mass increases
  18. 18. Newton‘s 2 nd Law If more force is applied, an object will be accelerated _____ more
  19. 19. Newton’s 2 nd Law • More force means more acceleration • More mass means less acceleration Force = mass X acceleration F = ma
  20. 20. Newton’s 3 rd Law For every action, there is an equal and opposite reaction. Forces occur only in pairs – Act on different objects – Equal and opposite
  21. 21. Newton’s 3 rd Law The hammer exerts a force on the nail to the right. The nail exerts an equal but opposite force on the hammer to the left.
  22. 22. Momentum
  23. 23. Terminal Velocity The final speed of a falling object.
  24. 24. Terminal Velocity Air resistance is offsetting the the weight of the object
  25. 25. Forces End
  26. 26. Force Aristotle's idea: For an object to move at a constant speed, a constant force must be applied.
  27. 27. Force Newton’s idea: An object moving at a constant speed will continue at that speed without additional force being applied.
  28. 28. Balanced Forces

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