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Periodic  Motion   P2
 

Periodic Motion P2

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nice ppt of physics

nice ppt of physics

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    Periodic  Motion   P2 Periodic Motion P2 Presentation Transcript

    • Introduction to Periodic Motion CP Physics - Sly
    • Periodic Motion: a comparison Projectile motion was an object going up and coming down, ONCE! -vs.- Periodic motion is a repeating motion, that can be described with Newtonian physics and our kinematics equations.
    • So we will be looking at the following examples:
      • Circular Motion
      • Torque
      • Simple Harmonic Motion
      • (Springs and Pendulums)
      The only thing is that these situations require us to describe things differently.
    • The human body cannot sense constant velocity… But it has a great ability to sense small shifts in acceleration .
    • I. Circular Motion Remember that acceleration is a change in speed or direction.. So an object spinning in a circle can have constant speed, but since its direction is changing, the velocity is changing and therefore acceleration. In circular motion its called Centripetal Acceleration . * Centripeta l: meaning center seeking or towards the center.
    • Centripetal acceleration It it a difficult derivation, that I do not want to spend time on, but based on taking two points very close together on a circle (that can be connected by a tangent), we get… a c =  v = v 2  t r
    • What is Uniform Circular Motion?
      • Based on the car looping around the track, what do you gather?
    • Understanding a circle to understand velocity
      • Remember that circumference = 2  r
      • Trig tells us one complete cycle is the period (T)
      • So velocity is distance around circle divided by time
      • V = 2  r
      • T
    • Why use this for velocity? This makes it easier to determine the velocity of the object, since distance and time can be measured without interfering in the motion.
    • Put these two equations together. (derive as a class)
    • We also have a force
      • Since there is acceleration toward the center, there is also a force towards the center …
      Centripetal Force F c = ma c = mv 2 = m(4  2 r) r T 2
    • Circular Motion cont. Lets look at this in action…
    • One last item, fictional forces
      • To compensate, objects in an accelerating reference frame invent fictional forces to explain motions in Newtonian terms.
      • In circular motion, this fictional force is called centrifugal force, or in outward direction opposite of centripetal.
      • WHY? (based on momentum)
    • So think about riding in a car
      • Consider riding along in a car with your crazy friend, the one who likes to take turns 50 mph. What forces do you feel in a turn to the left in this scary song?
      If you say a force to the right then you have identified centrifugal force due to your body wanting to move in a straight line.  NOT A REAL FORCE When you press against the door, the door applies a centripetal force (along with friction on the seat) to make you turn.