Forces and Motion

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Forces and Motion
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Why do objects move?

• A force acts on them
• A FORCE is a push or a pull, in any
  direction,that may cause a change in an objects
  motion

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Will a force always cause an object to move?

• NO

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Every object has several forces always acting on
them.
Gravity
Air Pressure
Air Pressure
Friction
Friction
Normal
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The sum of all the forces acting on an object is
called NET FORCE

• If an object is motionless, the Net Force 0 ,
  The forces are said to be Balanced. With Balanced
  Forces, the forces are equal but in opposite
  directions

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Since the applied force is not stronger than the
force of friction the object does not move
The forces are said to be Balanced
Gravity
Air Pressure
Air Pressure
Applied Force
Friction
Normal
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• If a force is exerted on an object causing it to
  move, this is called an UNBALANCED FORCE, the net
  force is greater than zero and the object moves.

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If the applied force is strong enough to over
come the existing forces, the object will move
The applied force is stronger than friction this
is an example of an Unbalanced force
Gravity
Air Pressure
Air Pressure
Friction
Applied Force
Normal
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Some Common Forces
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Friction

• The force exerted when two objects rub up against
  each other.
• Friction opposes motion, it causes objects to
  slow down

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What affects the Friction between objects?

• Mass of the Object
• Type of Surface
• Amount of surface area touching

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Sliding Friction
Motion
Friction
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Rolling Friction
The amount of friction between the two objects is
less than sliding friction
The object is easier to move
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Liquid Friction
A lubricant, such as oil, makes a thin layer
between the two objects.
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Which one will move farther if an equal force is
applied
200 kg
1000 kg
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Which one will move farther if an equal force is
applied
On ICE
200 kg
On Carpet
200 kg
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Which one will move farther if an equal force is
applied
200 kg
200 kg
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Gravity

• The force that pulls objects towards each other
• Every object has gravity, meaning that all
  objects are being pulled toward each other.
• So why are we not being pulled together right now?

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The larger the object is, the more we are
effected by its gravitational pull.
We are more attracted to the Earths gravity than
we are to gravity of the things in the room
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Where will the red ball move
Since the green ball is bigger, its gravity
effects the red ball more than the white ball
does, so the red ball moves towards the green ball
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Why do the two objects not hit the ground at the
same time?

• Gravity is acting more on the elephant than on
  the feather. And a heavier object overcomes the
  upward force of wind resistance (friction) more
  easily thus falling faster than the light object

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• What happens if we can eliminate the wind
  resistance?

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The two objects hit the ground at the same time
Gravity is still acting more on the elephant than
the feather, but the inertia of the elephant
keeps it from accelerating faster
All objects will accelerate the same when the
force of gravity is the only force action on it.
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Sir Isaac Newton and the 3 Laws of Motion
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Inertia

• The resistance of an object to changes in motion
• Basically Stated its harder to alter the motion
  of a heavier object than a lighter object

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Newtons First Law

• An object in motion will stay in motion and an
  object at rest will stay at rest until acted on
  by a force.
• Basically stated objects keep moving until
  something slows them down (friction) and objects
  will stay still until something causes them to
  move (force)

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Newtons First Law AppliedAs the wall stops the
car the guy keeps going, there is nothing to
stop his forward motion
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Newtons First Law Appliedas the truck stops,
there is nothing keeping the ladder from
stopping it continues to move forward until
gravity and wind resistance stops it
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Newtons Second Law

• Shows the relationship between an objects mass
  its acceleration and the applied force.
• Basically stated it takes a stronger force to
  move a heavier object that a lighter object and a
  stronger force to get an object to move faster

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Newtons Second Law AppliedIf an equal force is
applied, the less massive object moves farther
200 kg
1000 kg
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Newtons 2nd Law Applied In order to move the
more massive object the same distance at, it will
take a much larger force
200 kg
1000 kg
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Newtons Third Law

• For every action, there is an opposite and equal
  reaction
• Basically stated apply a force in one direction,
  there is the same force being applied right back
  at you

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Action Thrust
Reaction Jet moves forward
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As the swimmer pushes against the water, the
water pushes back and the swimmer moves forward
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Which Law Applies
If you step off a boat, the boat is moved backward
THIRD LAW
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Which Law Applies
Second Law its harder to throw a heavy object
than a light one
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Which Law Applies?
Third Law the downward force causes the space
ship to go up
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Which Law Applies?
2nd law it takes a big force to mover the heavy
object
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First Law The object will not move until
something causes it to move
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Would this cart be able to make the loop on this
roller coaster?
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Newtons 3rd law says every action has an equal
reaction
Here is the action force
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Remember.. Equal not greater
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So the reaction force can only be this high
Here is the action force
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The cart would only go this high then fall back