Force

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Force Newtons Laws

• .

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Newtons First Law

• Force- a push or a pull

Ex. Throwing a ball
force
gravity
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Forces

• Net Force-

The combination of forces acting on an
object -determines the motion of the object
Frictional Force, Gravitational Force, Tensional
Force, Electrical Force, Normal Force, Magnetic
Force, Air Resistance Force, Applied Force,
Spring Force
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Forces

• Net Force-

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Balanced Unbalanced Forces

• Balanced Forces 2 or more equal forces whose
  effects cancel each other out and DO NOT change
  the objects motion

No movement
Ex. Tug of war Holding a book
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Balanced Unbalanced Forces

• Unbalanced Forces 2 or more unequal forces
  acting on an object causing the object to
  accelerate.

Yes movement
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Newtons First Law of Motion

• States that objects at rest will remain at rest
  or move with a constant velocity unless a force
  is applied (inertia)

1st understood by Galileo Galileii 1564-1642
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Older Ideas About Motion

• Natural State of Rest

Galileo-
Naturally at Rest or Naturally in Motion

• No force needed to keep
• an object moving!!

So WHY does an object stop?!
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Friction-

• Force that acts to resist sliding between 2
  touching surfaces.

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Types of Friction

1. Static
2. Sliding
3. Rolling

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Types of Friction

• Static Friction friction that prevents an
  object from moving when a force is applied
• -caused by the attraction between atoms

roughness- mass- static friction
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Types of Friction

• 2. Sliding Friction slows down a sliding object
• -due to microscopic roughness of the surfaces

Ex. Brake pads on a car Bicycle brakes
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Types of Friction

• 3. Rolling Friction occurs between a wheel and
  the ground
• -needed to make a wheel or tire turn- keeps
  tire from slipping on the ground

(less than sliding friction)
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Newtons 2nd Law !

• States that an object acted upon by a net force
  will accelerate in the direction of the force

Net force mass
Acceleration
F m
a
Fma
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Newtons 2nd Law !

• Units of force Newtons (N)

Fma Fkg m/s/s
1 kg m/s/s 1 N
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Fma
500 kg

• F 500kg x 3 m/s/s

F 1500 N
3 m/s/s
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Fma

• F 5kg x 9.8 m/s/s

5 kg
F 49 N
9.8 m/s/s
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Fma
200 kg

• F 200kg x 2 m/s/s

F 400 N
2 m/s/s
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GRAVITY

• Gravity The force that tends to pull all
  objects toward the center of the Earth.

- measured as weight
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LAW of GRAVITATION

• -The gravitational force between two objects is
  directly proportional to the product of their
  masses and inversely proportional to the square
  of the distance between them.

3 PARTS
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1.

• -Any 2 pieces of matter will pull on each other
  with a certain gravitational force

d
Planet Bob
Planet Gary
F
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2.

• -The amount of matter in the objects determines
  the size of the force

Mass gravity
Earth
Moon
F
F
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3.

• -The distance between the objects affects the
  size of the force.

Distance gravity
Distance gravity
.5d
Planet Bob
Planet Gary
4xF
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Gravitational force Between 2 objects

• mass of object1 x mass of object 2
• (Distance between objects) 2

m1 x m2 (d)2
g
100m
500kg
100kg
Planet Gary
Planet Bob
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g

• m1 x m2
• (d)2

100kg x 500kg (100m)2

50,000kg 10,000m2
5N
100m
500kg
100kg
Planet Gary
Planet Bob
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Using Newtons 2nd LAW

• Turning net force is at an angle

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Circular Motion

• -direction constantly changing
• Constantly accelerating
• - Force is constantly applied

Centripetal Force- always perpendicular to the
direction of motion
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Satellite Motion

• -direction of motion

8 km/s Or 28,800 km/h
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Air Resistance- Air pushing against you

• -Friction

Gravity Terminal Air resistance
Velocity

Speed air resistance
200km/h 300km/h
20km/h
Amount depends on shape
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Newtons 3rd LAW of Motion !

• -States that forces always act in equal but
  opposite pairs.

-For every action (force) there is an equal and
opposite reaction (force)
Gravity
table
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Action Reaction forces dont cancel

• Ex. A rocket launch

Reaction
Movement
Action
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Weightlessness
Bob

• Measuring weight - scale

Weightlessness- The condition that occurs in free
fall when the weight of an object SEEMS to be
zero.
scale
Bob
scale
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Weightlessness

• Weightlessness in Orbit
• freefall around the Earth