A pointlike object moves with constant speed
along the circumference of a circle of radius
R.
At each instant t
its position vector r=r(t)
is indicated in the video.
We let the video start to move at the instant
t=0
when the position vector of the object
makes an angle of zero degrees
with the horizontal.
We stop the video when the particle has made five complete revolutions.
However, in the back of our mind the particle neither starts to move,
nor stops to move, but has always been rotating in the past
and will continue to rotate forever (like the Earth around the Sun
or the electron-proton system).
We only set our measurement of time equal to
t=0
at one of the many times that its position vector
makes an angle of zero degrees with the horizontal.
|
|
