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ACCELERATIONACCELERATION
Science 10 – Physics UnitScience 10 – Physics Unit
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Comparing Types of MotionComparing Types of Motion
• Uniform motion– Moves in a straight line with constant velocity
•Speed and direction are constant•Feels smooth or like no motion is occurring
• Non-uniform motion -- acceleration– Speed and/or direction is changing
•Feels like being pushed or pulled
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ACCELERATIONACCELERATION
•Acceleration is a rate (over time) of change in velocity
•Occurs whenever–Speed changes–Direction changes
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ACCELERATIONACCELERATION• Acceleration (a) is calculated as
• a = ∆ v = v2 – v1 change in velocity
∆t = t2 – t1 change in time
• Acceleration units are derived from velocity units (m/s) over time units (s)
• Acceleration units are m/s/s = m/s2
a = Δv = m/s Δt s
a = Δv Δt
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Equation ManipulationEquation Manipulation
Δt = tf – ti
Δt + ti
tf – Δt
Δv = vf – vi
Δv + vi
vf – Δv
a = Δv Δt
a Δt
Δv a
tf =
ti =vi =
vf = Δv =
Δt =
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a = vf – vi
tf – ti
vf – vi = a (tf – ti)
ti = tf = vf – vi
a
a = Δv Δt
Δv = a Δt
Δt = Δv a
Equation ManipulationEquation Manipulation
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Practice Practice unit unit recognitionrecognition
Measurement
• 25m
• 25s
• 25m/s
• 25m/s2
Property
Time
Velocity
Acceleration
Position
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AccelerationAcceleration
• BIG Acceleration means velocity is
CHANGING QUICKLY
– Means speed changes in short time
interval
– Means direction changes in short time
interval
– DOES NOT MEAN big velocity
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AccelerationAcceleration
• Small Acceleration means velocity is
CHANGING SLOWLY
– Means speed changes in long time
interval
– Means direction changes in long time
interval
– DOES NOT MEAN small velocity
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Comparing AccelerationsComparing Accelerations
• Instantaneous acceleration – acceleration at a specific moment in time (*snaps)
• Average acceleration – acceleration which occurs over a time interval
• When acceleration is constant, – average equals instantaneous
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Comparing AccelerationsComparing Accelerations
• Positive Acceleration means
velocity is INCREASING
–more speed over time
–away from origin over time
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Comparing AccelerationsComparing Accelerations
• Negative Acceleration means
velocity is DECREASING
–less speed over time
–toward origin over time
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Check Your Understanding:Check Your Understanding:
Which measurement is an acceleration?
(a) 25s(b) 25m/s(c) 25m/s/s(d) 25m
Which measurement shows greatest acceleration?
(a) 25m/s 5s
(b) 25m/s 2s
(c) 25m/s 10s
(d) 25m/s 25s
UNITS!Smallest
time interval
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Comparing ConstantsComparing Constants
Constant “velocity” vs Constant “acceleration”
• Constant velocity = no change in velocity – acceleration = ZERO
• Constant acceleration = no change in rate of velocity– Velocity is changing at a constant rate
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Visualizing AccelerationVisualizing Acceleration• metronome and marker (ticker timer)
Positive acceleration
•• • • • • – more distance in same time, increasing velocityNegative acceleration
• • • • • •– Less distance in same time, decreasing velocity
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Visualizing AccelerationVisualizing Acceleration
• Velocity-Time Graphs – effect of time on velocity – Velocity labeled on y-axis– Time labeled on x-axis
• Slope (line) represents acceleration• The steeper the slope, the greater
acceleration – the greater the CHANGE IN velocity
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Time(s)
Velocity
(m/s)
0 10
1 10
2 10
3 10
4 10
5 10
Flat line represents ZERO acceleration Flat line represents ZERO acceleration – zero change in velocity --- constant – zero change in velocity --- constant
velocityvelocity
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Time(s)
Velocity
(m/s)
0 0
1 10
2 20
3 30
4 40
5 50
Smooth sloping line upward Smooth sloping line upward represents increasing velocityrepresents increasing velocity
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Smooth sloping line downward Smooth sloping line downward represents decreasing velocityrepresents decreasing velocity
Time(s)
Velocity(m/s)
0 50
1 40
2 30
3 20
4 10
5 0
a = - 10m/s2 = slope
Ve
loci
ty (
m/s
)
time (s)
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Curved slope means changing Curved slope means changing accelerationacceleration
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A. At which time interval is acceleration greatest?
B. At which time interval is acceleration zero?
C.How long does it take the object to slow to a stop?
D.What is the Δv of the blue line between 1s & 2s?
0-2s
4-7s
3s
Practice Analysis
5m/s
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A. Which line shows negative acceleration?
B. Which line shows zero acceleration?
C.Which line shows greatest constant acceleration?
D.Which line shows changing acceleration?
Blue (A)
Blue (A)
Purple (C)
Practice Analysis
E
(E)
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Calculating accelerationCalculating acceleration
a = vf – vi
tf – ti
Suppose a car going in a straight Suppose a car going in a straight line is moving at 35km/hr at 3 line is moving at 35km/hr at 3 seconds and 50km/h at 8 seconds. seconds and 50km/h at 8 seconds. What is the accelerationWhat is the acceleration of the car? of the car?
Given Unknown Equation Solution Sentence
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Calculating accelerationCalculating acceleration
a = vf – vi
Δt
What is the accelerationWhat is the acceleration of a of a vehicle that changes its velocity vehicle that changes its velocity from 100 km/h to a dead stop in from 100 km/h to a dead stop in 10s?10s?
G U E S S
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Calculating time intervalCalculating time interval
a = vf – vi
Δt
When the shuttle bus comes to a sudden When the shuttle bus comes to a sudden stop to avoid hitting a dog, it accelerates stop to avoid hitting a dog, it accelerates uniformly at 4.1m/suniformly at 4.1m/s22 as it slows from 9.0m/s to as it slows from 9.0m/s to 0m/s. 0m/s. FindFind the the time intervaltime interval of acceleration for of acceleration for the bus.the bus.
G U E S S
Δt = vf – vi
avf – vi = aΔt