Dynamics

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Dynamics
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Momentum

• Momentum - Newton called it Quantity of motion.
• Ex. Find the momentum of a 40 kg ball traveling
  with velocity

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Newtons 1st Law

• Newtons 1st Law - A body maintains constant
  velocity unless acted on by an outside force.

• Inertia - A bodys resistance to change in motion.

• This law defines an inertial frame of reference.

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Newtons 2nd Law

• Newtons 2nd Law - The rate of change in momentum
  is equal to the net force acting on the body.

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Additional Info

• Will use summation notation for net force.
• Units for force
• From dimensional analysis
• In metric will use a newton (N)

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Fundamental Forces

• Gravitational - Masses attract
• Electrical - Unlike charges attract
• Magnetic - Unlike poles attract
• Weak - Responsible for radioactive decay
• Strong - Holds the nucleus of the atom together.

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Rounding the Curve

• Ex. A car travels around a curve of radius 120 m
  at 24.5 m/s. If the car has a mass of 750 kg,
  what is the force of the road on the tires of the
  car?

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Weight

• Weight - The force due to gravity.
• Ex. You and your bike weigh 882 N. If your
  brakes can exert a force of 200 N, what stopping
  distance do you need if you are traveling at 11
  m/s?

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Elevator Ride

• You stand on a scales while in an elevator. You
  know you weigh 150 lbs, but the scales say you
  weigh 180 lbs. What is happening in the elevator?

• It is stationary.
• It is moving upward at constant v.
• It is moving downward at constant v.
• It is moving upward at increasing v.
• It is moving downward at increasing v.
• It is accelerating upward.
• It is accelerating downward.

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Elevator (Cont.)

• Ex. You stand on a scales while in an elevator.
  You know you weigh 150 lbs., but te scales say
  you weigh 180 lbs. What is your acceleration?

Fs
W
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Hot Air Balloon

• Ex. Fred and Jane are in a hot air balloon,
  which is acceleration upward at 0.05 m/s². How
  much lift is the balloon supplying given the
  following masses?

mfred 150 kg
mjame 50 kg
mballoon 85 kg
mcarriage 150 kg
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Newtons 3rd Law

• Newtons 3rd Law - The force exerted on A by B is
  equal and opposite to the force exerted on B by A.

• Ex. A 110 kg skydiver accelerates towards the
  earth at 9.8 m/s². How does the earth respond to
  him?

mearth 5.97 1024 kg
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Hookes Law

• Hookes Law - The force exerted by a spring is
  proportional to the distance the spring is
  compressed or stretched from its rest state.

k - spring constant (N/m)

• This is a restoring force. It opposes the
  displacement from its rest state.

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Shock Absorbers

• Ex. What is the spring constant of your shock
  absorbers if they compress 15 cm when supporting
  110 kg of your cars mass?