VELOCITY
Science Starter - Calculating Time Answers…
1.
How long would it take a cat walking north at
0.80 m/s to travel 12 m north?
(15s)
2.
A car is driving forward at 15 m/s. How long
would it take this car to pass through an
intersection that is 11 m long?
(0.73s)
Objective
•SWBAT calculate velocity
given distance and time
information
Agenda
•Science Starter
•Review Last Class
•Intro to New Material
What is speed?
Speed: how fast something is moving or
how much distance is covered in a certain
amount of time.
We will discuss two types of speed: (write)
•Instantaneous speed: An object’s speed
at any given instant.
•Average speed: An average of all
instantaneous speeds.
Velocity
•Velocity is the same as speed,
but it has a direction
associated.
•Speed has no specific
direction.
Average Velocity (write)=
To calculate average speed
•average speed = total distance/time
s = d/t
If you cover 75 m in 3 sec, how fast are
you going?
Answer: 25 m/s
If you travel 20 m/s for 10 m, how long
did it take you?
Answer: .5 s
Video
•https://www.khanacademy.or
g/science/physics/onedimensionalmotion/displacementvelocity-time/v/calculatingaverage-velocity-or-speed
Question
•Can something have a constant
speed but a changing velocity?
•Yes. All it has to do is turn.
•Remember: Velocity includes
direction; speed does not.
Practice
•A man walks 7 km East in 2
hours and then 2.5 km West in 1
hour.
a) What is the man's average
speed for the whole journey?
b) What is the man's average
velocity for the whole journey?
average
speed =
average
velocity =
distance
time
displacement
time
=
7 km + 2.5 km
2 hours + 1
hour
=
9.5 km
3 hours
= 3.2 km/h
(approximate
d to the
nearest tenth)
=
7 km - 2.5 km
2 hours + 1
hour
=
4.5 km
3 hours
= 1.5 km/h
Practice
•You start walking from a point on a
circular field of radius 0.5 km and 1
hour later you are at the same point.
a) What is your average speed for
the whole journey?
b) What is your average velocity for
the whole journey?
A.
average
speed =
distance = circumference
time
time
=
2 * 0.5 * Pi
1 hour
= Pi km/h =
3.14 km/h
(approxima
ted)
B. If you walk around a circular field
and come back to the same point
where you started the displacement,
which a change in position, is equal
to zero. Since the displacement is
equal to zero, the average velocity is
also equal to zero.
Converting between m/s and km/h
•
To convert from km/h to m/s:
•
•
Change km to m: 1 km = 1000 m
Change h to s: 1 h = 3600 s
Multiply by 1000 and divide by
3600
or
• Divide the speed in km/h by 3.6 to
obtain the speed in m/s.
For example, convert 75 km/h to m/s.
•
75 km
1h
1000 m   1h 
 
 
  21 m/s
 1km  3600 s 
Converting between m/s and km/h
Try the following unit conversion problems.
1. Convert 95 km/h to m/s.
2.
A truck’s displacement is 45 km north
after driving for 1.3 h. What was the
truck’s average velocity in km/h and m/s?
3.
What is the displacement of an airplane
flying
480 km/h [E] during a 5.0 min time
interval?
Answers are on the next slide.
Converting between m/s and km/h Answers
Convert 95 km/h to m/s.
(26m/s)
2. A truck’s displacement is 45 km north
after driving for 1.3 h. What was the
truck’s average velocity in km/h and m/s?
(35 km/h [N], 9.6 m/s [N])
1.
3. What is the displacement of an airplane
flying
480 km/h [E] during a 5.0 min time
interval?
(40 km [E] or 40, 000 m [E])