Is there a negative velocity? if so how is it achieved?
Velocity has two components, speed and direction. Speed can be
measured in whatever units you like, say miles per hour. Direction is defined
by the person doing the measurement. So, if I define one direction to
be positive I will have a positive velocity when travelling in that
direction. I will have a negative velocity when travelling in the
The point is: you cannot have a negative _speed_
many physical quantities, BY DEFINITION, cannot be negative
some examples: speed, mass, measurements of size, the direction
of time, temperature (in the Kelvin scale),...
extra credit: think of some more things that cannot be negative
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Update: June 2012