Transcript Section 3.1 - CPO Science

Motion and Force
Chapter Three: Motion
• 3.1 Position and Velocity
• 3.2 Graphs of Motion
• 3.3 Acceleration
Investigation 3A
Positive and Negative Position
• How do we measure position in two
dimensions?
3.1 The position variable
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Motion is about knowing where things
are and how they move.
To understand where things are, we
need to understand position.
3.1 The position variable
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Position is a variable and it is always
relative to an origin, or the place where
the object’s starting point was zero.
3.1 Forward and backward
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Position and distance
are similar but not the
same.
Both use units of length.
Distance can have only
positive values.
3.1 Forward and backward
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Position uses positive and negative numbers.
Positive numbers are for positions to the right
(in front) of the origin.
Negative numbers are for positions to the left
(or behind) the origin.
3.1 Forward and backward
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Many variables can be positive or negative.
These include position, speed, and force.
These variables are called vectors because
they can have a value and a direction.
We use the term
velocity to mean
speed with direction.
3.1 Keeping track of where you are
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Pathfinder is a small robot sent to
explore Mars.
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It landed on Mars
in 1997.
Where is
Pathfinder now?
3.1 Keeping track of where you are
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Pathfinder keeps track of its velocity
vector and uses a clock.
Suppose Pathfinder moves forward at
0.2 m/s for 10 seconds.
What is Pathfinder’s velocity?
3.1 Keeping track of where you are
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Suppose Pathfinder goes backward at
0.2 m/s for 4 seconds.
What is Pathfinder’s velocity?
What is Pathfinder’s change in position?
3.1 Keeping track of where you are
• The change in position is the velocity
multiplied by the time.
3.1 Keeping track of where you are
• Each change in position is added up using
positive and negative numbers.
• Pathfinder has a computer to do this.
3.1 Maps and coordinates
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If Pathfinder was crawling on a straight board,
it would have only two choices for direction.
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Out on the surface of
Mars, Pathfinder has
more choices. The
possible directions
include north, east,
south, and west, and
anything in between.
3.1 Maps and coordinates
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Pathfinder’s exact position can be
described with two numbers.
These numbers are called coordinates.
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This graph shows
Pathfinder at
coordinates (4, 2) m.
3.1 Maps and coordinates
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The graph can also show any path
Pathfinder takes, curved or straight.
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This kind of graph
is called a map.
Street maps often
use letters and
numbers for
coordinates.
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3.1 Vectors on a map
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Suppose you run east for 10 seconds at a
speed of 2 m/s.
Then you turn and run south at the same
speed for 10 more seconds.
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Where are you
compared to where
you started?