• Do Now: In 1911, the fastest aircraft could travel
approximately 90 mph and the fastest cars could do a little more
than 100 mph. One hundred years later, these numbers seem
small compared to space shuttles that travel over 17,000 mph
and rocket-powered cars that can break the sound barrier.
Currently, one of the fastest legal stock street cars is the
Hennessey Venom GT, which can reach top speeds of 260 mph.
Suppose you take a trip in this vehicle for one hour.
1. Is your speed of 260 mph relative to the car? (yes/no)
2. Will you travel exactly 260 miles?
3. More than 260 miles?
4. Less than 260 miles?
Explain #1-4!
(And copy down your HW!)
•
http://www.top10fastest.com/fastest_cars_2013/
2.2 Speed
Instantaneous Speed
A car does not always move at the same speed.
You can tell the speed of the car at any instant by
looking at the car’s speedometer.
The speed at any instant is called the
instantaneous speed.
2.2 Speed
The speedometer gives readings of
instantaneous speed in both mi/h and km/h.
2.2 Speed
Any combination of units for distance and time that are
useful and convenient are legitimate for describing speed:
• miles per hour (mi/h)
• kilometers per hour (km/h)
• centimeters per day
• light-years per century
2.2 Speed
Average Speed
In a trip by car, the car will certainly not travel at
the same speed all during the trip. (You speed up,
slow down, stop, go etc…)
The driver cares about the average speed for the
trip as a whole
The average speed is the total distance covered
divided by the time.
2.2 Speed
Average speed can be calculated easily ( we will
practice this later in class):
For example, a distance of 240 kilometers during a time
of 4 hours is an average speed of 60 km/h:
2.2 Speed
If we know average speed and travel time, the distance
traveled is easy to find.
•So, how can we solve for TOTAL DISTANCE
COVERED? Using basic algebra….
•Does anything CANCEL?
2.2 Speed
If we know average speed and travel time, the distance
traveled is easy to find.
x
So, if your average speed is 80 kilometers per
hour on a 4-hour trip, then you cover a total
distance of _________________?
TRY IT! (on looseleaf, or in the margin of Ch. 2 Guided
Notes…work with the people around you, 1 minute!)
2.2 Speed
So, if your average speed is 80 kilometers per hour on a
4-hour trip, then you cover a total distance of _________?
x
x
4h
4
1
x
80 km
h
80 km
=
= 320 km
•Does anything CANCEL?
•So we are left with…
•Let’s check…does km make sense if we are solving for
DISTANCE?
Your First Set of Equations!!!
The Δ (DELTA )
means “change in”
Add the Delta
to your notes!
USE ALGEBRA…
Write the “distance”
formula using symbols…
USE ALGEBRA…
Write the “time” formula
using words…
AND symbols!
Δt . s =
d
Δt . s =
Change in time =
Total distance covered
Divided by average
speed
Δt =
d___
s
d
Known
s= 7 m/s
Δt = 150 s
Show All Work
Unknown
Formula
Known
s= 7 m/s
Δt = 150 s
Show All Work
Unknown
d=?
Formula
Known
s= 7 m/s
Δt = 150 s
Show All Work
Unknown
d=?
Formula
d= s
.
Δt
Known
Unknown
s= 7 m/s
Δt = 150 s
d=?
Show All Work
d= s
.
Δt
Formula
d= s
.
Δt
Known
s= 7 m/s
Δt = 150 s
Show All Work
d = s . Δt
d= 7m
s
Unknown
d=?
Formula
d= s
.
Δt
Known
s= 7 m/s
Δt = 150 s
Unknown
d=?
Show All Work
d = s . Δt
d = 7 m . 150 s
s
Formula
d= s
.
Δt
Known
s= 7 m/s
Δt = 150 s
Unknown
d=?
Show All Work
d = s . Δt
d = 7 m . 150 s
s
1
Formula
d= s
.
Δt
Known
s= 7 m/s
Δt = 150 s
Unknown
d=?
Show All Work
d = s . Δt
d = 7 m . 150 s
s
1
Does anything cancel?
Formula
d= s
.
Δt
Known
s= 7 m/s
Δt = 150 s
Unknown
d=?
Formula
d= s
.
Show All Work
d = s . Δt
d = 7 m . 150 s
s
1
d = 7 m . 150 = 1050 m
CHECK - Does meters make sense for distance?
Δt
Known
Unknown
s= 7 m/s
Δt = 150 s
d=?
Formula
d= s
Show All Work
d = s . Δt
d = 1050 m
1
.
3.2808 ft = 3444.84 ft
1m
.
Δt
Known
s= 7 m/s
Δt = 150 s
Unknown
d=?
Formula
d= s
.
Show All Work
d = s . Δt
d = 7 m . 150 s
s
1
.
3.2808 ft = 3444.84 ft
1m
Δt
Closing
• Take BACK your do now Pre Assessment
• Now that you have LEARNED how to correctly do
this…
– Review
– FIX any errors in
a different color (see me if you
need a red pen) so I can see your thought process
– Questions/ comments/ concerns? Write them in the
margin!
– Turn back in as your exit slip
– Have a great day 