► Whatis the closest thing to uniform motion that
you have ever observed?
► What factors might prevent objects from moving
uniformly on Earth or in space?
► Whatother phenomena besides uniform motion
cannot be observed directly, even in the best lab,
and must be inferred from imperfect observations?
► Predicting the behaviour of moving objects
can be very complex..
► uniform motion: motion at constant
velocity, with no change in speed or
How can you tell if an object is
► Youneed to check whether it has constant
velocity: neither its speed nor its direction is
► Direction: must be moving in a straight
line, forward or back, up or down.
► Speed: can be measured in many ways,
including speedometers, radar guns etc.
Remember: Graph shapes of uniform
Position-time graph of tightrope walker:
Average or Instantaneous?
► Instantaneous velocity : the velocity of a moving
object at one specific moment.
► Average velocity: velocity measured over a certain
► In many situations like getting a speeding ticket,
average velocity is less important than
instantaneous velocity. Explain why in your own
Calculating average velocity from a
► Each section of the graph
has a different slope
velocities at that stage of
► Calculate them by finding
individual slopes of that
section of the graph.
► The average velocity of the
total graph or trip is found
by using the beginning and
Pause & reflect:
► Sketch a position-time graph of each object listed
below. Describe its slope as positive or negative,
and as constant, increasing, or decreasing.
► A) a stone at rest
► B) a jogger moving steadily to the right
► C) a bicycle moving to the left and slowing down
► D) a rocket moving up at an increasing speed
► E) a stone falling freely with increasing speed
► F) a parachutist drifting down at a steady speed
► Pg 329 #1-4