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Direction of displacement,velocity and acceleration in an oscillation

  1. Apr 9, 2012 #1
    Hi,good morning. I encountered a problem regarding simple harmonic motion. I have seen the graphs of displacement, velocity and acceleration in an oscillation. How to determine the Direction of displacement,velocity and acceleration in an oscillation? I really have no idea

  2. jcsd
  3. Apr 10, 2012 #2


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    hi hikarigenzo! :wink:
    i don't understand what you're asking about :confused:

    can you give an example? :smile:
  4. Apr 10, 2012 #3
    Simple harmonic motion is defined (in one way) as the motion resulting when a force is proportional to a displacement and directed back towards the equilibrium point.
    Displacement is a vector... distance from equilibrium point.
    Acceleration is proportional to force (a=F/m) and is therefore directed towards the equilibrium point
    Velocity.... depends on position
  5. Apr 10, 2012 #4
    Thanks for the replies, I should rephrase my question. The positive or negative sign in displacement in the oscillation depends on what? For example, a pendulum that oscillates vertically, how do we give the positive or negative? Is it based on the direction like upwards positive and downwards negative or positive is given to the position above the equilibrium? Thanks. I reply quite slow because I am now preparing for exam.
  6. Apr 11, 2012 #5


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    hi hikarigenzo! :smile:
    for a pendulum, it's arbitrary …

    you can make left positive, or you can make right positive, it makes no difference

    for a bungee jumper, you'd make up positive, simply because making down positive would be annoying (but you could make down positive if you really wanted to)

    for a spring, you'd usually make extension positive, but you don't have to, and if two springs are joined together, you often make extension positive for one and extension negative for the other

    to sum up …

    it's arbitrary, don't worry about it! :biggrin:
  7. Apr 11, 2012 #6

    Thanks. I got it
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