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Newton's Laws & Gravitation
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  • Remember that Force is also a vector - it has to include direction in the answer.
  • If I send a ball rolling across the floor, it will continue at the same speed and direction unless it encounters another force. What forces might it encounter
  • If I send a ball rolling across the floor, it will continue at the same speed and direction unless it encounters another force. What forces might it encounter
  • If I send a ball rolling across the floor, it will continue at the same speed and direction unless it encounters another force. What forces might it encounter

Transcript

  • 1. Newton's Laws & Gravitation
  • 2. Newton's Second Law
    • Newton's Second Law: When an object is acted on by an unbalanced force, it will accelerate (speed up, slow down or change direction) in the direction of that force.
      • In other words, if you push on an object, the amount that it accelerates depends on two things:
        • the mass of the object (bigger mass = more inertia)
        • the magnitude of the force with which you push
    • Force = Mass x Acceleration (F=ma)
  • 3. F=ma
    • Force = Mass x Acceleration
    • Force = 10 kg x 10 m/s 2
    • 100 kg • m/s 2 = 100 Newtons
    • Force = 100 N to the right
    100 N 10 kg 10 m/s 2
  • 4.
    • Force = Mass x Acceleration
    • 100 N = 100 kg x ? m/s 2
    • ? N = 100 kg x 10 m/s 2
    1 m/s 2 1000 N 100 kg ? m/s 2 100 N 100 kg 10 m/s 2 ? N
  • 5.
    • Force = Mass x Acceleration (F=ma)
    • Force = 1,000 kg x .05 m/s 2
    • Force = 50 kg • m/s 2
    • (kg • m/s 2 = Newtons)
    • Force = 50 N East
    Calculating Force East
  • 6. Practice Problem
    • Force = Mass x Acceleration (F=ma)
    • Find the net force.
    • Plug in the #'s for force and acceleration.
    • Solve for acceleration.
    Answer: A 3 kg • m/s 2  100kg = 0.03 m/s 2 to the left
  • 7. Newton's Third Law
    • Newton's Third Law : for every action there is an equal and opposite reaction.
      • "action" & "reaction" are the result of forces
      • the forces don't act on same object
        • the "action" is on one object (i.e. woman pushes cart)
        • the "reaction" is on another (i.e. cart exerts force on woman)
  • 8. GRAVITY
    • Gravity is a pull (force) between any two objects that have mass, such as the earth and an object on its surface.
    • The gravitational force between two masses is directly proportional to the mass of each object.
      • The more "stuff" you've got (mass), the more gravitational attraction there is.
    • The gravitational force between two masses is inversely proportional to the distance between those two objects.
          • The more space between your "stuff" and mine, the less gravitational attraction there is.
  • 9. LAW OF UNIVERSAL GRAVITATION
    • Two things affect gravity:
      • Mass of objects
      • Distance between objects
    • G = 6.672x10 -11
    • (Universal Gravitational Constant)
    • F g measured in Newtons (N)
  • 10. Projectile Motion
    • What do Newton's Laws of Motion say about this cannon?
      • The cannon & ball will not move unless acted on by an unbalance force (explosion within the cannon)
      • The ball will accelerate proportionately to the amount of force (the bigger the "bang" inside the cannon, the faster the ball accelerates.
    Newton's Cannon
      • The cannon will "kick" back in response to an equal and opposite force exerted from the ball exploding forward.
      • The pull of gravity results in centripetal acceleration, where the ball continually "falls" around the earth in orbit.
  • 11. Free Fall
    • When the only force acting on a falling object is gravity, it is said to be in free fall .
    • As an object falls, it picks up speed.
      • Gravity causes the rate at which it falls to increase (accelerates, speeds up).
    • All objects fall at the same rate.
      • Earth produces the same acceleration on an object, no matter what it's mass is: 9.8 m/s 2 toward the ground .
      • In reality, some objects fall slower due to air resistance
      • Without air resistance (in a vacuum), all objects fall at an identical speed
  • 12. Acceleration Due to Gravity
    • Both objects accelerate at the same rate.
    • Both objects will reach the ground at the same time.
  • 13. Terminal Velocity
    • When the forces of gravity and air resistance equal out, an object reaches terminal velocity .
      • This means the falling object will no longer accelerate (it won't get any faster)
    skydiver illustration
    • When the skydiver opens a parachute, it dramatically increases air resistance.
      • This counters the force of gravity and slows the skydiver down.
  • 14. Weight vs. Mass
    • Mass = how much "stuff" a thing has
      • ...the amount of matter in an object
      • Measured with a balance
      • Stays the same regardless of gravity
    • Weight = gravity's pull on that "stuff"
      • Weight = mass x acceleration due to gravity
      • Measured with a spring or digital scale
      • Weight is a force, measured in Newtons
    • W = m • g
  • 15. Calculating the Force of Weight
    • Weight = m x g
    • m (mass) has to be in kg
    • g (acceleration due to gravity) = 9.8 m/s 2
    For a 150 lb person: W = 68 kg x 9.8 m/s 2 W = 666 Newtons