# Direction of displacement,velocity and acceleration in an oscillation

1. Apr 9, 2012

### hikarigenzo

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

Thanks

2. Apr 10, 2012

### tiny-tim

hi hikarigenzo!

can you give an example?

3. Apr 10, 2012

### truesearch

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

4. Apr 10, 2012

### hikarigenzo

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.

5. Apr 11, 2012

### tiny-tim

hi hikarigenzo!
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!

6. Apr 11, 2012

### hikarigenzo

Thanks. I got it