# Waves-displacement vs movement

How can a particle move downwards and be displaced upwards? Sounds paradoxical. I understand the part about movement but not displacement. What's the difference? Isnt displacement like the amplitude so when a particle in a transverse wave move down doesnt it mean its displaced downward?

Simon Bridge
Homework Helper
How can a particle move downwards and be displaced upwards?
The same way a skiier can be displaced a long way up a mountain but be moving (skiing) down it.
You have already met this sort of thing in your work on Newton's laws of motion.

I understand the part about movement but not displacement. What's the difference? Isn't displacement like the amplitude so when a particle in a transverse wave move down doesn't it mean its displaced downward?
When you displace a string in the +y direction, and let go, which direction does it move in? What physical quantity describes "movement"?

I'm sorry i still dont get the skiing part too :( hmm movement the physical qty is distance??

Simon Bridge
Homework Helper
for movement, the physical quantity is "momentum" but I'd accept "velocity".
for position, the physical quantity is "distance", I'd accept "displacement".

something can have a positive displacement and a negative velocity if it is headed back to the origin.
have you not covered Newton's laws yet? kinematics? v-t graphs?

I have covered newton's law and i understand that part. I think i got you now :) so a particle will be displaced downwards irregardless of movement when it is below the eqm position?( in a graph of sinusoidal waves diagram)

Simon Bridge