# Opening Ideas

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```					     Uniform and
Instantaneous Velocity
Opening Ideas:
► 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?
Uniform Motion
► Predicting  the behaviour of moving objects
can be very complex..
►   uniform motion: motion at constant
velocity, with no change in speed or
direction.
How can you tell if an object is
moving uniformly?
► Youneed to check whether it has constant
velocity: neither its speed nor its direction is
changing.

► Direction:  must be moving in a straight
line, forward or back, up or down.

► Speed:  can be measured in many ways,
Remember: Graph shapes of uniform
motion:
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
time interval.

► In many situations like getting a speeding ticket,
average velocity is less important than
instantaneous velocity. Explain why in your own
words.
Calculating average velocity from a
position-time graph:
►   Each section of the graph
has a different slope
representing individual
velocities at that stage of
the journey.
►   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
end points.
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
Homework:
► Pg   329 #1-4

```
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