constant & changing motion
DESCRIPTION
Constant & Changing Motion. Reference Point. A fixed point from which direction is defined. The reference point can be anything. Distance. The length traveled measured from start to finish. Use meters!!!. Example #1. - PowerPoint PPT PresentationTRANSCRIPT
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Constant & Changing Motion
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Reference Point
A fixed point from which direction is defined.
The reference point can be anything.
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Distance
The length traveled measured from start to finish.
Use meters!!!
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Example #1
A car drives 4 meters north, 3 meters south, then 5 meters north. What’s its total distance driven?
D = 4m + 3m + 5m
D = 12m
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Direction
Represented by using :
(+) or (-) signs
Up or Down
Right or Left
Forward or Backward
North, South , East or West
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Position
Where something is, relative to the reference point.
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Displacement
The net difference between the starting point and the ending point.
d = dfinal – dinitial
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Example #2
A car drives 4 meters north, 3 meters south then 5 meters north. What’s its displacement?
Δd = 9m north – 3m south
Δd = 6m north These are the vectors that we’ve been practicing!
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Time Interval
The difference between two clock readings
t = tfinal – tinitial
Use seconds!!!
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Speed
Total distance traveled divided by the total time elapsed.
speed = distance/time
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Average Velocity ( Vavg)
Total distance traveled divided by the total time elapsed.
Vavg = d/t Units: m/s
Magnitude (size) and direction
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Average Velocity
1 mile 2 miles 2 miles3 seconds1 second 2 minutes
home Dairy
Queen
4 hr.
EXXON
3 hr.
5 miles
Δt includes ALL time, whether you were moving or not!
Δt = 1 sec + 14400 sec + 120 sec + 10800 sec + 3 sec
Δt = 25324 sec (x 1 hr / 3600 sec = 7.03 hr)
Vavg = 5 mi / 7.03 hr
Vavg = 0.71 mi/hr
LHS
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What is the difference between speed and velocity?
•Velocity is a vector quantity (magnitude & direction)
•Speed represents the magnitude of velocity (scalar quantity)
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Instantaneous Velocity (V)
•Velocity at one point
•Δd and Δt are very, very, very, very……small!
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Constant Velocity
•If a body is moving at a constant velocity, the velocity never changes between intervals.•Doesn’t happen often in real life!•Ex:
V = 10 m/s V = 10 m/s V = 10 m/s
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Changing Velocity
•Here, the velocity changes between intervals.
•Ex:
V = 10 m/s V = 15 m/s V = 20 m/s
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Acceleration
•Acceleration is the change in velocity over time.
•Average acceleration (aavg ) = change in velocity
time spent
•aavg = ΔV / Δt
•Units: (m/s) m
s s2
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Acceleration Example #1•Find aavg.
Vi = 10 m/s Vf = 40 m/s
aavg = 40 – 10 m/s
2 s
*This means that the object’s velocity increases 15m/s every
second!
aavg = 15 m/s2
Δt = 2 sec
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Acceleration Example #2•Find aavg.
Vi = 40 m/s Vf = 10 m/s
aavg = 10 – 40 m/s
2 s
*This means that the object’s velocity decreases 15m/s every
second!
aavg = -15 m/s2
Δt = 2 sec
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Acceleration Example #3•Find aavg.
Vi = 40 m/s Vf = 40 m/s
aavg = 40 – 40 m/s
2 s
*This means that the object’s velocity is constant!
aavg = 0 m/s2
Δt = 2 sec
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Four Basic Equations of Physics
• Conditions:– One-dimensional motion– Constant acceleration
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Four Basic Equations of Physics•Vf = Vi + at
•d = Vi t + ½ at2
•2ad = Vf2 – Vi
2
• Vf + Vi
2d =
t