Speed, velocity and acceleration

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Speed, velocity and acceleration

• Physics 100 Chapter 2

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speed
distance traveled elapsed time
speed v
Hawaii Kai? Haleiwa In one hour
50km 1 hr
v
50km/hr
50km
This is the average speed over 1 hour. For
shorter time intervals it can be higher or
lower.
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Earths motion around the Sun
r1.5x1011m
distance elapsed time
2 p r
2 x 3.14 x 1.5 x 1011m 365 days x 24 hrs/day

V

1year
9.4 x 1011 m 8.76 x103 hrs
9.4 x 1011 m 8760 hrs
1.1x108 m/hr


1.1x105 km/hr
? 70,000 mi/hr
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Velocity speed direction
6 months later speed same different direction
v
r1.5x1011m
velocity is a vector a quantity that has both
magnitude and direction
Length of the arrow speed Direction of arrow
same as direction of the motion
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Scalars and Vectors
Simple numbers Speed v Temperature T
Number direction Velocity v relative
positions r Force F Acceleration a
Campus Center
r
PSB
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Acceleration (? changes in v)
change in velocity elapsed time
acceleration
change in v elapsed time
a
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Change in V 100km/hr Elapsed time 3 sec
change in v elapsed time
a
103 m
100km/hr 3 s
33 km/hr s

3600 s 3.6x103s
33x103m 3.6x103 sxs
9.1 m/s2

This baby goes from 0 to 100km/hr in only 3
seconds
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Different ways to change V
v
v
Car speeds up
a
v
v
screech!
Car slows up
a
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Accelerations (continued)
v
v
Car turns
a
In all three cases, v changes. Therefore these
are all examples of accelerations
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Free Fall
11
t0 v00
dist time
5m 1 s
vavg

5m/s
0 v1 2
v0 v1 2
v1 2
vavg


5m
v1 2vavg
10 m/s
t1s v1?
V1 10 m/s
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Free-fall acceleration
10m/s
change in velocity elapsed time
acceleration
1s
10m/s 1s
a
g
10 m/s2
This is called the acceleration due to gravity
and given the special symbol g10m/s2
Actually g9.8m/s2. But 10 m/s2 is close enough
for us.
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Free fall from greater heights
t 0s
Total distance
V0 0
5m
5m
t 1s
V1 10m/s
15m
20m
t 2s
1 2
gt2
V2 20m/s
25m
t 3s
45m
V3 30m/s
35m
t 4s
80m
V4 40m/s
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Upward toss
Total height
t 4s
V4 0
80m
5m
V3 10m/s
t 3s
75m
15m
60m
V2 20m/s
t 2s
1 2
gt2
v0t-
25m
V1 30m/s
35m
t 1s
35m
V0 40m/s
t 0
0m
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Simple rule for free fallaka projectile motion

• When Earths gravity is the only force involved
• actual height height for no gravity ½gt2

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Horizontal toss
t 0s
t 1s
t 3s
t 4s
t 2s
5m
20m
45m
80m
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upward toss
t 4s
t 3s
t 2s
45m
80m
20m
t 1s
5m
t 0s
18
Shoot the monkey
dead white European male
communist
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Shoot the DWEM Slower bullet
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Very fast horizontal toss
t 0s
t 1s x 8km
t 2s x16km
t 3s x24km
V8km/s
5m
20m
45m
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Orbital motion is free fall
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Artificial satellite
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Turning car
An object free to slide on the
dashboard, tries to follow a straight line path