sect. 8.1 speed
TRANSCRIPT
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Motion is when an
object changes
position.
Speed (s) is how fast /
slow it changes position.
To calculate speed, we need
1. Distance (how far it went)
2. Time (how long it took)
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Calculating Speed
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HOW
FASTAM I?
Walking person
1.4 m/s
(3.1 mph)
Cruising jet
257 m/s
(575 mph)
Speeding race car
96 m/s
(215 mph)
Flying eagle51 m/s
(114 mph)
Galloping horse
19 m/s
(42 mph)
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To Solve Problems,
use the blocks !!!
INFO ANSWER
with
units!
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Speed Calculation ExamplesFlorence Griffith Joyner set a world record by
running 220 m in 21.34 s. What was heraverage speed?
INFO
d = 220m
t = 21.34s
s = ?
ANSWER
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Speed Calculation ExamplesThe worlds fastest passenger elevator operates
at an average speed of 10 m/s. If the 60th floor is219 m above the first floor, how long does it takethe elevator to go from the 1st to the 60th floor?
INFOd = 219m
t = ?
s = 10m/s
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Distance-Time GraphsAllows us to see the motion of an object.
x-axis:
time (s)
y-axis:
distance
(m)
A straight line =
constant speed.
Slope = change in distance = avg. speed
change in time
Flat slope (horizontal) = at rest.
Steeper slope = faster speed.
s = +
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Graphing Speed Example
TIME DISTANCE
0 min 0 m
10 min 800 m
20 min 1600 m
30 min 2400 m
TIME DISTANCE
0 min 0 m
10 min 400 m
20 min 400 m
30 min 1200 m
Swimmer 1 Swimmer 2
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Speed of Two Swimmers
0 5 10 15 20 25 30
Time (minutes)
2400
22002000
1800
1600
1400
1200
1000
800
600
400
200
0
D
i
s
ta
n
c
e
(m)
What is the total distance
the 1st swimmer swam?
The second swimmer?2400 m
1200 m
What is the avg. speed of
the 1st swimmer?
The second swimmer?
s = d = 2400 m = 80 m/min
t 30 min
s = d = 1200 m = 40 m/min
t 30 min
Compare the avg. speedof the 2ndswimmers 1st
10 min to her last 10 min.1st = 400/10 = 40 m/min
Last = 800/10 = 80 m/min
Her s eed doubled!
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Speed or Velocity?
Velocity is simplyspeed with a direction!
An escaped ostrich heading
toward our campus at 16.2 m/s.
A kitten running up
a tree at 6.5 m/s.
A car heading west on I-10 at 50 mph.
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Momentum
The product of an objectsmass and its velocity.
momentum = mass x velocity
p = mv
UNITS:
m = kg
v = m/s
p = kg m/s
small mass
small velocity
small momentum
large mass
large velocitylarge momentum
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Calculate the momentum of a
6.00 kg bowling ball moving at10.0 m/s down the alley.
INFO
m = 6.00 kg
v = 10.0 m/sdown the alley
p = ?
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ACCELERATION
How fast the velocity is changing!
+ acceleration = speeding up
- acceleration = slowing down
UNITS: a = m/s = m/s2
s
acceleration = final velocityinitial velocity
time
a = VFVI = Vt t
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Velocity-Time GraphAllows us to see the change in the
velocity of an object.
x-axis:
time (s)
y-axis:
velocity
(m/s)
A straight line =
constant
acceleration.
Slope =
acceleration
flat slope (horizontal) = constant velocity
+ slope = speeding up (+ acceleration)
- slope = slowing down (- acceleration)
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As a roller coaster starts down a
hill, its speed is 10m/s. Threeseconds later, its speed is 32 m/s
at the bottom of the hill. What is
the roller coasters acceleration?
INFO
VI = 10 m/s
VF = 32 m/st = 3 s
a = VFVI / t
a = (32 m/s - 10 m/s) / 3 s7.3 m/s2downward
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CH 8 SEC 1 & 2 REVIEW Know the units for distance, time, mass,
speed, velocity, momentum, acceleration.
Be able to calculate
- speed/velocity
- momentum
- acceleration
from a word problem.
Be able to interpret
- speed
- acceleration
graphs.
(**KEEP IN MIND: You will be given all formulas in the
format they will appear on the
TAKS formula sheet.**)
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OBJECT TRIAL
1
TRIAL
2
TRIAL
3
AVERAGE
TIME (s)
SPEED
(cm/s)
v=d/t
MASS
(g)
MOMENTUM
(gm/s)
p=mv
Bouncy
Ball
Racquet /
Sponge
Ball
Golf/Ping
PongBall
Car
DATA TABLE
P L b Q ti
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Pre-Lab Questions1. Rank the following objects from 1-4. Your number
1 should be the object that you think will have the
fastest speed/velocity down the ramp.
Bouncy Ball, Racquet / Sponge Ball,
Golf / Ping-Pong Ball, Car
2. Explain why you have ranked the objects in the
order.
3. What are units we usually use to measure speed?
4. Since this is a science class, and we measure in
metric units, what are units that we can measure
speed in?
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Conclusions
1. Why is finding an average of three trialsmore accurate than just one trial?
2. Which object had the fastest speed, whichhad the slowest?
3. Did your results surprise you? Explain whyor why not.