Forces and Motion PS9.21 PS9.22 PS9.23 PS9.24 ps9.25

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Forces and MotionPS9.21PS9.22PS9.23PS9.24ps9.
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• Forces can create changes in motion 3 types of
  acceleration (change in speed or direction
• (acceleration) speeding up
• Deceleration is negative acceleration or slowing
  down
• Centripetal acceleration changing direction

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Motion can be described as

• a change in an objects position
• Average velocity (speed) is the change of
  position of an object over time

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Velocity Graphs V distance time

• Velocity (v) is the slope (rise over run) of a
  position (d) vs. time (t) graph

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40 The diagram represents the total travel of a
teacher on a Saturday. Which part of the trip is
made at the greatest average speed? F Q G R H S J
T
How do we work this one? Calculate v d/t for
each segment.
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Acceleration Graphs

• Acceleration (a) is the slope of a velocity (v)
  vs. time (t) graph
• Plotted on a distance vs. time graph,
  acceleration is an exponential curve

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Acceleration is a change in an objects velocity
(speed or direction)

• When an objects speed changes over time it is
  accelerating (or decelerating)
• A vfinal vinitial
• time
• Units for acceleration m/s/s or m/s2

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Definition of a Force

• A Force is a push or a pull

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Balanced Force

• A force that produces no change in an objects
  motion because it is balanced by an equal,
  opposite force.

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Unbalanced Forces

• Are forces that results in an objects motion
  being changed.

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Friction

• A force that acts in a direction opposite to the
  motion of two surfaces in contact with each other.

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Friction

• Friction causes an object to slow down and stop.
• Since the amount of energy stays constant, the
  energy becomes heat.

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Newtons 1st Law of Motion

• Object in motion stays in motion

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Newtons 1st Law of Motion

• And Objects at rest stay at rest

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Newtons 1st Law of Motion

• Until they are acted upon by unbalanced forces.

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Inertia or Newtons 1st Law

• Tendency for an object to stay at rest or moving
  in a straight line at a constant speed.
• The mass (m measured in kg) of an object
  determines its inertia

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Newtons 2nd Law of Motion

• Force Mass X Acceleration
• Fma
• Weight (pull of gravity) is a
• commonly measured force, calculated by Fmg, g
  is the acceleration due to gravity 9.8 m/s2

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Newtons 2nd Law of Motion

• The greater the mass of an object, the greater
  the force required to change its motion.

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Newtons 2nd Law of Motion

• The greater the acceleration of an object, the
  greater the force required to change its motion.

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11 The frog leaps from its resting position at
the lakes bank onto a lily pad. If the frog has
a mass of 0.5 kg and the acceleration of the leap
is 3 m/s2, what is the force the frog exerts on
the lakes bank when leaping?

• A 0.2 N
• B 0.8 N
• C 1.5 N
• D 6.0 N

Formula chart says Fma, m is mass in kg, a is
acceleration in m/s2. So, .5 kg x 3 m/s2 1.5 N
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Newtons 3rd Law of Motion

• For every action force there is an equal and
  opposite reaction force.

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Newtons 3rd Law of Motion

• All forces come in action-reaction pairs
• Ex feet push backward on floor, the floor pushes
  forward on feet

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Universal Law of Gravitation

• Between any two objects in space there is gravity

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Universal Law of Gravitation

• Gravity varies depending on two factors

1) the mass of the object doing the pulling, and
2) the distance from the center of that object
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On Earth gravity 9.8 m/s/s

• For every second that an object falls its speed
  increases by 9.8 m/s