Ch 11 velocity and acceleration
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Transcript Ch 11 velocity and acceleration
Ch 11
Motion
A change in position
Motion
How
do you know
something has moved?
Frame of reference (reference point) =
system of objects that are not moving with
respect to one another
Relative Motion = movement in relation
(or relative) to a frame of reference
http://www.sciencebook.dkonline.com/161.html
Distance versus Displacement
Distance is the length of a path
between two points
SI Unit is meter (m)
Displacement is the length
from the starting point to the
ending point
Examples:
What is the total distance traveled?
4m + 2m + 4m + 2m = 12m
What is the total displacement?
ZERO
How is the speed limit measured?
Miles per hour
What 2 things are
considered?
–Distance (miles)
–Time (hour)
Speed
the ratio of the distance (d)
an object moves to the
amount of time (t) the object
moves
SI Unit is meter per second
(m/s)
V=d/t, d=Vt, t=d/V
Distance
Velocity
time
Speed
Average speed = computed for
the entire duration of the trip
Instantaneous speed = measured
at a particular instant
Velocity (V) = the speed &
direction an object is
moving
Vector = a quantity that
has magnitude & direction
Same speed &
direction =
velocity
Graphing speed
distance-time graph
200
180
Distance (m)
160
140
120
100
80
60
40
20
0
0
2
4
Time (s)
6
8
10
Distance-Time graph
Slope tells me SPEED!
Horizontal part tells me the object
stopped moving=no motion=no velocity
Straight portions tell me constant
speed
Greater the slope the higher the speed,
vice versa
Distance-Time Graphs
Constant low speed
500
400
300
200
100
0
distance(m)
distance (m)
Constant High Speed
0
5
10
time (s)
15
20
500
400
300
200
100
0
0
5
10
time(s)
15
20
Distance-Time Graphs
Varying Speed
500
distance(m)
400
No motion=stopped
300
200
100
0
0
5
10
time(s)
15
20
Florence Griffith Joyner set a world
record by running 200m in 21.34s.
What was her average speed?
Sound travels at a speed of 330m/s. If
a lightning bolt strikes the ground
1000m away from you, how long will it
take for the sound to reach you?
STAR cards
What is a reference point?
An objects that is not moving
What are the units for speed?
Meters per second
What does the horizontal line
on a Distance-Time graph
mean?
That the object is not in motion, it’s still
Acceleration
Is the rate at which velocity
changes
changes in speed
changes in direction
changes in speed & direction
SI unit is meter per second per
second (m/s2)
Acceleration
The triangle is the
Greek symbol
delta, means
“change in”
Vf = final velocity
Vi = initial velocity
Vf-Vi
(final minus initial)
V
a
t
Why are the seconds squared?
Vf – Vi
ΔV
a
t
SI unit is meter per second per second (m/s2)
Distance-Time graph for the cars,
Which car goes with which line?
Red=B
Blue=A
Green=C
Distance-Time Graph
Changing Velocity over time
140
120
Distance (m)
100
80
Curved parts tells me object is
increasing & decreasing speed =
changing velocity over a time period
= acceleration
60
40
20
0
0
1
2
3
Time (s)
4
5
Speed-Time graph
Slope tells me acceleration!
Horizontal part tells me object is
at constant speed (velocity) = no
acceleration
Slope downward tells me object
is slowing down (decelerating or
negative accleration)
Graphing constant acceleration
Speed-Time Graph
30
Speed (m/s)
25
20
15
10
5
0
0
1
2
Time (s)
3
4
Speed-Time Graph
Positive Acceleration
Negative Acceleration
20
7
18
6
16
5
speed (m/s)
14
Speed (m/s)
Constant
speed/velocity
12
10
8
6
4
3
2
4
1
2
STOPPED!
0
0
0
1
2
time (s)
3
4
0
5
10
time (s)
15
20
The speed limit changes from 55m/s
to 0m/s. To make the change in
10s, what acceleration will it
require?
2
3m/s .
A car’s acceleration is
if the
car started at rest and it only took
10s for the car to reach this
acceleration, what is the car’s final
velocity?
2
A=9.8m/s
Vf=0.5m/s
Vi=?
t=3s
STAR cards
What is a vector?
a quantity that has magnitude & direction
What is acceleration?
Is the rate at which velocity changes
What does horizontal part on a speed-time graph tell
me?
object is at constant speed (velocity) = no acceleration
What does horizontal part of a distance-time graph tell
me?
No speed, no motion, object is stopped
What does curved part on a distance-time graph tell
me?
Acceleration