Newton's Laws
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Newton's Laws

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A summary of Newton's 1st, and 2nd laws.

A summary of Newton's 1st, and 2nd laws.

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Newton's Laws Newton's Laws Presentation Transcript

  • Chapter 4 section 1 The first law of motion
    • If the net force acting on an object is zero, the object remains at rest
    • Or, if the object is moving, it continues in a straight line with constant speed
    • What’s another way to say “net force equals zero”?
  • Unbalanced Forces Change Velocity
    • Skateboard at rest stays at rest until you push it.
    • The velocity increases while you are pushing it-unbalanced forces
    • Why does it slow down and stop?
    • The unbalanced frictional force acts to slow it down- change the velocity
  • Inertia and Mass
    • All objects have a property called inertia
    • It is the tendency of an object to resist an change in its motion
    • A dirt bike rider trying to take a corner as fast as he can
    • The inertia of an object depends on the mass
    • The greater the mass the greater the inertia
  • Inertia and the First Law of Motion
    • The first law of motion is sometimes called the law of inertia
    • What happens in a head on car crash?
    • The car stops, but the passenger not wearing a seat belt continues to move forward at the same speed the car was going. In about 0.02 s the person hits the dashboard
    • Force and acceleration are related
    • Throwing a ball with greater force has greater acceleration than a gently thrown ball
    • And
    • Mass and acceleration are related
      • The greater the mass the smaller the acceleration
      • Softball vs baseball
        • Assume you throw with same force, the softball has less velocity and acceleration
      • Acceleration depends on mass as well as net force
  • The Second Law Motion
    • States that acceleration of an object is in the same direction as the net force on the object
    • Calculated a = f /m
    • Change this equation to calculate force:
    • f= m/a
  • Quiz
    • Gravity depends on the ___________ of the objects and the _____________ between them.
    • Newton’s first law states that in order for an object’s velocity to change, forces must be _____________.
    • What is inertia?
    • What is inertia directly related to?
    • 2 nd law: Acceleration depends on _________ and _____________.
    • Acceleration is in the same____________ of the net force.
    • What is centripetal force?
  • Projectile Motion
    • Projectile is something that is shot through the air, ie a softball
    • Forward force gives it horizontal movement
      • After you let go, the velocity is constant
      • But there is also vertical motion caused by gravity
    • Important point: horizontal and vertical motion are independent, but together make the movement look curved
  • What if you…
    • Pitched a baseball forward and at shoulder height and dropped one straight to the ground from the same height? Which one would get to the ground first?
    • They would get there at the same time- horizontal and vertical motion are independent of each other
  • Centripetal Force
    • The net force toward the center of a curved path
    • Any force which keeps an object moving in the curved path instead of shooting off straight.
    • Examples?
    • The force of gravity
    • Friction
  • This week
    • Thursday: review for test
    • Friday: test
    • If you miss the test, the make-up will most definitely be more DIFFICULT
    • If you plan on being gone tomorrow, get the review from me today b/c you will still have to take the test
  • Review
    • A projectile is what?
    • Vertical motion and horizontal motion of a projectile are ____________ of each other
    • What is the net force toward the center of a curved path?
    • What is another way to say that?
    • Example?
  • 4.3 Newton’s 3 rd Law
    • When one object asserts a force on another, the second object exerts a force that is equal in strength and opposite in direction
    • What is another way to say that?
    • For every action there is an equal and opposite reaction
  • Action and Reaction Forces do not cancel
    • Just b/c an action produces an equal and opposite reaction, that doesn’t mean the forces balance
    • The forces are acting on different objects
  • Momentum
    • Momentum is related to how much force is needed to change an objects motion
    • Momentum= mass multiplied by velocity
    • M = mv
    • Another way to say this would be?
    • The greater the mass and/or velocity, the greater the momentum
  • Law of Conservation of Momentum
    • The momentum of an object doesn’t change unless its mass and/or velocity change
    • Momentum can be transferred from one object to another
    • Pool ball example