PowerPoint Version - Adams Science News
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Lab Report Due Friday
Any questions on the report?
A Graphs of Motion
Update Your TOC
Video
https://www.youtube.com/watch
?v=x2ve5yucNPQ
https://www.youtube.com/watch
?v=ohYQMEhl5Cc
Parts of a Graph
X-axis
Y-axis
All axes must be labeled with appropriate units, and values.
Position vs. Time
The x-axis is always “ time ”
The y-axis is always
“ position/distance”
The slope of the line indicates the velocity of the object.
Slope = (y
2
-y
1
)/(x
2
-x
1
)
d
1
-d
0
/t
Δd/Δt
1
-t
0
Velocity = distance time
Position vs. Time
14
12
10
8
6
4
2
0
20
18
16
1 2 3 4 5 6 7 8 9 10
Time (s)
Uniform Motion
Uniform motion: equal displacements occurring during continuous equal time periods (constant velocity)
Straight lines on position-time graphs mean uniform motion.
Acceleration / Velocity
Acceleration: rate of which an object changes its speed
(changing how fast an object is moving)
An object is accelerating if its speed or direction is changing
A= change in velocity change in time
Δ v
Δ t
Velocity is the how fast it’s moving. It is measured in m/s .
Acceleration
If an object is not changing its velocity (how fast it’s moving), then the object is not accelerating.
Acceleration
The data at the right are representative of a northward-moving accelerating object.
The velocity is changing over the course of time.
In fact, the velocity is changing by a constant amount - 10 m/s - in each second of time.
Anytime an object's velocity is changing, the object is said to be accelerating; it has an acceleration .
http://www.physicsclassroom.com/mmedia/kinema/acceln.cfm
Which car or cars ( red , green , and/or blue ) are undergoing an acceleration ? Study each car individually in order to determine the answer. (write it in your NB)
If you inspect each car individually, you will more likely notice that only the green and the blue cars accelerate. The red car moves with a constant speed, covering the same distance in each second of the animation.
The green and the blue cars are speeding up, thus covering an increasing distance in each second of the animation.
http://www.physicsclassroom.com/mmedia/kinema/acceln.cfm
Watch the changing of each car(s) velocities. Which is slower change? Which is a faster change? Which has no change?
The red car is moving with a constant velocity
The green car has a more gradually changing velocity
The blue car has a faster changing velocity http://www.physicsclassroom.com/mmedia/kinema/acceln.cfm
Check with your partner
Talk to your neighbor
Explain to them what speed, velocity, and acceleration are
Write down in your notebook the similarities and the differences
Speed
Velocity
Acceleration
Consider the position-time graph at the right. Each one of the three lines on the position-time graph corresponds to the motion of one of the three cars. Match the appropriate line to the particular color of car.
http://www.physicsclassroom.com/mmedia/kinema/acceln.cfm
The red car is moving with a constant velocity and must correspond to object B which has a constant slope.
The green and blue car s have a changing velocity and must correspond to lines with a changing slopes - objects A and C. The green car is object C which has a more gradually changing slope than object A (blue car).
http://www.physicsclassroom.com/mmedia/kinema/acceln.cfm
Steepness of slope on Position-Time graph
Slope is related to velocity
Steep slope = higher velocity
Shallow slope = less velocity
Positive and Negative Acceleration
increase in speed: positive acceleration
decrease in speed: negative acceleration .
Velocity vs. Time
Velocity vs. Time
X-axis is the “time”
Y-axis is the “velocity”
Slope of the line = the acceleration
20
18
16
14
12
10
8
6
4
2
0
1 2 3 4 5 6 7 8 9 10
Time (s)
Velocity vs. Time
Horizontal lines = constant velocity
Sloped line = changing velocity
Steeper = greater change in velocity per second
Negative slope = deceleration
Different Velocity-time graphs
Constant velocity?
Acceleration?
Deceleration?
Different Velocity-time graphs
Constant velocity?
Acceleration?
Deceleration?
Different Velocity-time graphs
Velocity vs. Time
20
15
10
5
0
1 2 3 4 5 6 7 8 9 10
Time (s)
Velocity vs. Time
25
20
15
10
5
0
1 2 3 4 5 6 7 8 9 10
Time (s)
Acceleration vs. Time
Time is on the x-axis
Acceleration is on the y-axis
Shows how acceleration changes over a period of time.
Often a horizontal line.
Acceleration vs. Time
12
10
8
6
4
2
0
1 2 3 4 5 6 7 8 9 10
Time (s)
Constant Rightward Velocity
Constant Leftward Velocity
Constant Rightward Acceleration
Constant Leftward Acceleration
Leftward Velocity with Rightward
Acceleration
Practical Application Velocity/Position/Time equations
Calculation of arrival times/schedules of aircraft/trains
(including vectors)
GPS technology (arrival time of signal/distance to satellite)
Military targeting/delivery
Calculation of Mass movement (glaciers/faults)
Ultrasound (speed of sound) (babies/concrete/metals) Sonar
(Sound Navigation and Ranging)
Auto accident reconstruction
Explosives (rate of burn/expansion rates/timing with det. cord)
Free Fall
Recognize the meaning of the acceleration due to gravity
Define the magnitude of the acceleration due to gravity as a positive quantity and determine the sign of the acceleration relative to the chosen coordinate system
Use the motion equations to solve problems involving freely falling objects
Freefall
Defined as the motion of an object if the only force acting on it is gravity .
No friction, no air resistance, no drag
Acceleration Due to Gravity
Galileo Galilei recognized about 400 years ago that, to understand the motion of falling objects, the effects of air or water would have to be ignored.
As a result, we will investigate falling, but only as a result of one force, gravity.
Weknowmemes.com
Galileo Galilei 1564-1642
Galileo’s Ramps
Because gravity causes objects to move very fast, and because the time-keepers available to
Galileo were limited, Galileo used ramps with moveable bells to “slow down” falling objects for accurate timing.
