Transcript Frames of Reference

•Frames of Reference
•1
•We look at events from a particular frame of
reference.
•Events look different from a different frame.
•All motion is relative – motion must be
compared to some reference point.
•Earth is the most common frame of reference.
•2
•Three axes are necessary to locate an object’s
position in three dimensional space (x,y,z).
•3
•At a constant velocity:
–From fixed frame of reference the path of the ball
is a parabola.
•4
–From the point of view of the cart the marble falls
straight down.
•The results are the same as when the cart was
not moving.
•There is no experiment that can tell you if you
are moving at a constant velocity!
•All frames are equivalent.
•5
•Sometimes we choose a moving frame.
•We choose the frame of reference that is most
convenient for us.
•6
•Velocity can be different depending on the frame of
reference.
•Law of Inertia – an object moves at a constant
velocity unless an unbalanced force acts on it.
•Some frames require several velocities to be added
or subtracted. u±v
•Relativistic physics is required near light speed.
•7
•In an accelerated frame of reference:
–Fixed frame- path of marble is parabola.
–Moving frame – ball moves backward.
•Non-inertial frame – frame of reference where
law of inertia does not seem to apply.
•Fictitious forces – explains motion in
accelerated frame of reference.
•(Coriolis and centrifugal forces are fictitious.)
•8
• A rotating frame is non-inertial.
•Fictitious forces explains motion in a rotating
(non-inertial) frame of reference.
•From fixed frame no unbalanced force is seen.
•Objects moving in a circle have an acceleration
toward the center called centripetal force.
•Centrifugal force is the fictitious force that
balances this by being exerted away from the
center.
•Centrifugal force exists in an accelerated frame
of reference.
•9
•The smaller the acceleration, the smaller the
fictitious force.
•Earth is a non-inertial (accelerating) frame of
reference, but it is barely noticeable.
•10
•Foucault's Pendulum demonstrates earth’s
rotation.