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Newton's Laws & Gravitation
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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.
      • 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