Transcript Chapter 11

Motion
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Motion: The change in position of an object
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Reference point: System of objects that are
as compared with a reference point
not moving (stationary) in respect to one
another
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Length of path
between 2 points
May not be
straight line
(shortest path)
Units: meters (m),
km, miles, cm,
etc.
Ex: Roads/streets
we drive
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The direction and
length in a straight
line from start to
end
ALWAYS includes
direction from start
point
Ex: walk 5 blocks
north from
McDonald’s
Ex: roller coaster
ride displacement
=0
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1.
2.
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How fast in a given amount of time
Distance traveled by object
Time to travel that distance
Units:
◦
◦
◦
m/s
mi/hr or mph
km/hr
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Average Speed - Calculated speed for trip
Ex) Ran marathon at 6 mi/hr
Instantaneous Speed - speed at exact moment
Ex) speedometer reading = 55 mi/hr
Object going an equal distance in equal amounts of
time = Constant speed (not speeding up or
slowing down)
 Doesn't
 45
mph
 4 m/s
tell the direction
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Expressed in m/s
Speed = Distance/Time
Or S = d/t
Ex: A car traveling at a constant speed and it
goes and distance of 645 m in 25 s. What is
the car’s speed?
S = d/t
S = 645m/25s
S = 25.8 m/s
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Graphs show speed/velocity
Time (independent variable) -> x-axis
Distance (dependent variable) -> y-axis
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Slope of line = speed
or velocity
Straight line =
constant speed
(cruise control)
Steeper slope =
faster speed
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Horizontal (flat)
line = object not
moving
Exs: stopped at
red light, parked,
at store
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Negative slope =
went backwards (neg.
displacement)
Ex: went to store,
shopped, and back
home
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Measurements:
Speed: m/s,
km/h, or m/h
Direction:
N (NE, NW), S
(SE, SW), East,
and West
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Describes both
speed and direction
of motion
Must give how
“fast” and direction
the object is going
Ex: 45 km going
South
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Can be described as changes in speed,
direction, or changes in both
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Small value = increasing gradually
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Larger value = speeding up more rapidly
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The slope of a speed-time graph is
acceleration
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Positive Acceleration – velocity increases or
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Negative Acceleration – velocity decreases or
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Horizontal line – on a velocity-time graph;
speeds up (gives a positive slope )
slows down (gives a negative slope )
stays constant, velocity does not change (----)
Any change in how fast or change in
direction
 Speed up
 Slow down
 Turn a corner
 Go around a curve
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Acceleration = change in velocity/time
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a = (final velocity – initial velocity)/time
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Measured in meters/second/second
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a = vf - vi/t
Calculating positive acceleration =
pos. # (speeding up)
 Ex: a = (80m/s – 0m/s)/20s = 4m/s
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Calculating negative acceleration =
neg. # (slowing down)
 Ex: a = (0m/s – 3m/s)/2s = 1.5 m/s
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Causes velocity change
 Unit = Newton (N)
 Net Force - combo of all forces acting
on object
 Net force = 0
Either stopped or constant speed
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2.
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2 Types of forces:
Balanced Forces - net force = 0
Forces cancel out
Ex) Fair tug of war
Unbalanced Forces - net force not = 0
One force is stronger
Car vs Train
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Physicist who described relationship between
force & motion
3 Laws: Newton’s Laws of Motion
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AKA – Law of Inertia
“An object at rest stays at rest, and an object
in motion stays in motion, unless acted upon
by an unbalanced force.”
Inertia = tendency of object to stay at rest
Exs: car crashes, magician table cloth trick
1st Law