Transcript Speed, velocity and acceleration

Speed, velocity and
acceleration
Physics 100 Chapter 2
speed
distance traveled
speed = v =
elapsed time
Hawaii Kai Haleiwa
In one hour
50km
v = 1 hr = 50km/hr
50km
This is the average
speed over 1 hour.
For shorter time
intervals it can be
higher or lower.
Earth’s motion around the Sun
r=1.5x1011m
V =
2pr
1year
distance
elapsed time =
1011
9.4 x
m
=
8760 hrs
=
11m
2
x
3.14
x
1.5
x
10
=
365 days x 24 hrs/day
9.4 x 1011 m
8.76 x103 hrs
= 1.1x105 km/hr
= 1.1x108 m/hr
 70,000 mi/hr
Velocity = speed + direction
v
r=1.5x1011m
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
Scalars and Vectors
Simple numbers:
Number + direction
Speed v
Temperature T
Velocity v
relative positions r
Force F
Acceleration a
r
PSB
Campus
Center
Acceleration ( changes in v)
change in velocity
acceleration =
elapsed time
a =
change in v
elapsed time
Change in V = 100km/hr
Elapsed time = 3 sec
a=
change in v
elapsed time
103 m
=
100km/hr
= 33 km/hr s
3s
3600 s
=3.6x103s
=
33x103m
2
=
9.1
m/s
3
3.6x10 sxs
“This baby goes from 0 to
100km/hr in only 3 seconds”
Different ways to change V
v
v
Car speeds up
v
Car slows up
a
v
a
Accelerations (continued)
v
a
In all three cases, v changes.
Therefore these are all examples of accelerations
Free Fall
t=0
5m
v0=0
dist
5m
vavg =
=
= 5m/s
time
1s
0
+
v
v
+
v
1 = v1
1 =
vavg = 0
2
2
2
v1 = 2vavg
t=1s
= 10 m/s
v1=?
V1 = 10 m/s
Free-fall acceleration
10m/s
change in velocity
acceleration =
elapsed time
1s
10m/s
ga =
1s
= 10 m/s2
This is called the “acceleration due to gravity”
and given the special symbol:
g=10m/s2
Actually g=9.8m/s2. But 10 m/s2 is close enough for us.
Free fall from greater heights
t = 0s
V0 = 0
5m
5m
t = 1s
V1 = 10m/s
Total
distance
15m
20m
t = 2s
V2 = 20m/s
1 gt2
2
25m
t = 3s
45m
V3 = 30m/s
35m
t = 4s
V4 = 40m/s
80m
Upward toss
t = 4s
t = 3s
80m
V4 = 0
V3 = 10m/s
5m
75m
15m
t = 2s
Total
height
V2 = 20m/s
60m
v0t- 1 gt2
25m
V1 = 30m/s
2
35m
t = 1s
35m
t=0
V0 = 40m/s
0m
Simple rule for free fall
aka: projectile motion
When Earth’s gravity is the only force
involved:
actual height = height for no gravity – ½gt2
Horizontal toss
t = 0s
t = 1s
t = 2s
t = 3s
t = 4s
5m
20m
45m
80m
upward toss
t = 3s
t = 2s
20m
t = 0s
t = 1s
5m
45m
t = 4s
80m
Shoot
dead white
communist
the European
monkey
male
Shoot the DWEM: Slower bullet
Very fast horizontal toss
t = 0s
V=8km/s
t = 1s
x= 8km
5m
t = 2s
x=16km
20m
t = 3s
x=24km
45m
Orbital motion is free fall
Artificial satellite
Turning car
An object
free to slide on the dashboard,
tries to follow a straight line path