Transcript Velocity and Acceleration

Ch 11
Motion
Motion
 A change in position
 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
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
 Florence Griffith Joyner set a world
record by running 200m in 21.34s.
What was her average speed?
 9.37 m/s
 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?
 3.03 s
 Velocity (V) = the speed &
direction an object is
moving
 Vector = a quantity that
has magnitude & direction
Same speed &
direction =
velocity
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
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 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
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