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As discussed, velocity and speed are two
different things in Science.
◦ Why? How are they different?
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Velocity can also, like speed, be constant or
changing.
◦ With changing velocity, an object has changed
speed, changed direction, or changed both speed
and direction.
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Velocity can be measured using a positiontime graph.
Turn to page 213 and analyze position-time
graphs considering:
◦ Positive slope
◦ Negative slope
◦ Zero slope
◦ Answer Part 1- #1, 2 and Part 2- #7
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We know the slope of a distance-time graph is
used to calculate the average speed of an
object.
Similarly, the slope of a position-time graph can
be used to find the average velocity of an
object.
slope = rise/run = Vav = d/ t = df – di / tf - ti
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Changes in velocity are referred to as acceleration, a.
◦ Acceleration can mean the speeding up or slowing down of an
object.
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Since acceleration measures changes in velocity, and
velocity is a vector quantity, acceleration is also a
vector quantity.
Position-time graphs can help us differentiate
between acceleration and uniform motion.
◦ Why are they not the same thing?
◦ In a position-time graph, a straight line indicates uniform
velocity and constant acceleration.
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A velocity-time graph shows us information on
the acceleration of an object.
◦ A straight-line velocity-time graph shows us that the
acceleration is constant. How?
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What will a graph with positive acceleration look
like?
◦ In a position-time graph? A velocity-time graph?
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What will a graph with negative acceleration look
like?
◦ In a position-time graph? A velocity- time graph?
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What does a distance-time graph tell us?
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What does a position-time graph tell us?
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What does a velocity-time graph tell us?
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How are the formulas for speed and velocity
different?
Examine the map on page 248.
◦ Calculate the average speed of the trip from
Annapolis Royal to Amherst.
◦ Calculate the average velocity of the same trip.
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Acceleration is directly related to velocity, so
the equation used to calculate it naturally
requires a velocity.
Unlike velocity, acceleration is calculated in
m/s^2
◦ This is because we are calculating how much the velocity
has changed; therefore 1.2 m/s^2 tells us the velocity is
changing by 1.2 m/s every second.
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aav = V/ t