Unit 12: Force and Motion / Lesson 1: Speed, Velocity, and Acceleration
MSF8.2c Distinguish the motion of an object by
its position, direction of motion, speed, and
acceleration and represent resulting data in
graphic form in order to make a prediction.
(DOK 2)
Motion: when an object’s position
changes from one place to another
Reference point: place or object
used to determine if something is
in motion.
• BEST type of reference point is an immovable
object
Speed: the distance an object travels in
one unit of time
•This is an example of a UNIT RATE
Formula to find speed:
*miles/1 hour (mph)
*meters/1 second (m/s)
*steps/1 minute
Constant speed: speed is the same at all times
during the motion or movement
Because objects do not usually travel a constant
speed over long distances, we find:
Average speed: total distance divided by total time
PRACTICE PROBLEM #1
Bethany walked 3 miles in 3 hours on Monday.
She then walked 6 miles in 5 hours on Tuesday.
On Wednesday, Bethany completed her journey
back home which consisted of 9 miles in 8 hours.
What was her average speed?
Total distance = 3 + 6 + 9 = 18 miles
Total time = 3 + 5 + 8 = 16 hours
Average speed = 18 miles = 1.1 mph
16 hours
PRACTICE PROBLEM #2
Mr. Hannigan types very quickly. For a
presentation, he typed 120 words in 2 minutes.
He went on to type 70 words in 1 minute.
Before finishing, he typed another 230 words in
3 minutes. How many words per minute did Mr.
Hannigan type?
Average speed = 420 words = 70 words per minute
6 minutes
Distance –Time Graphs
X-axis = time
Y-axis = distance
Slope: slant of line on graph = Speed
If it’s a: Straight line on the graph, then it =
constant speed
Comparing Speeds on a Distance Time Graph
•When comparing 2 lines on this type graph,
the steeper line = faster speed.
Which line
would mean
faster?
d
i
s
t
a
n
c
e
time
Distance Time Graph and Changing Speed.
Slope is decreasing = slowing down.
Horizontal line = no motion.
Slope is increasing = speeding up.
Velocity: speed in a given direction (north,
south, east, west, etc.)
*Hurricane Omar is moving at 25 kph in an easterly
direction toward the Cayman Islands.
*Maranda was driving at a speed of 65 mph west on
Highway 98 towards Columbia.
Basic unit
of length
in SI is
meter.
Smallest to
largest
mm, cm, m, km
Graphing motion
Scale: tells us how much or how many
•INTERVALS MUST BE EQUALLY
SPACED!
Points: show us the data that has been
collected
A line graph is useful for displaying data that
changes over time.
Which line would
mean faster?
distance
time
Distance-Time Graph Practice Problem #1
Which of
the graphs
show that
one of the
runners
started 10
yards
further
ahead of
the other?
Graph A
Distance-Time Graph Practice Problem #2
In Graph
D, which of
the runners
is fastest?
Runner #1
Distance-Time Graph Practice Problem #3
Calculate
the speed
of Runner
#1 for
Graph D.
S=d
t
S = 20 yd
4s
S = 5 yd/s
Distance-Time Graph Practice Problem #4
Calculate
the speed
of Runner
#2 for
Graph D.
S=d
t
S = 10 yd
4s
S = 2.5 yd/s
Acceleration.
• Acceleration is a measure of the change in
velocity during a period of time.
• An object’s velocity changes when it
speeds up, decreases speed, or changes
direction.
• Like velocity, acceleration has a direction
and can be represented with an arrow.
Average Acceleration
• Average acceleration is a change in velocity
during a time interval divided by the time
interval which the velocity changed.
•
Formula : a = Final speed – Initial speed
total time
Unit = m/s2
Velocity-Time Graph Practice Problem #1
Average acceleration =
Final speed - initial speed
total time
What is the average acceleration from 1.0-4.0
seconds?
At 1.0 seconds the initial velocity (or speed) is 40 m/s.
At 4.0 seconds the final velocity (or speed) is 100 m/s.
Average acceleration = 100 m/s - 40 m/s
3s
= 60 m/s
3s
=
20 m/s2
Velocity-Time Graph Practice Problem #2
Average acceleration =
Final speed - initial speed
total time
What is the average acceleration from 4.0-6.0
seconds?
At 4.0 seconds the initial velocity (or speed) is 100 m/s.
At 6.0 seconds the final velocity (or speed) is 60 m/s.
Average acceleration = 60 m/s - 100 m/s
2s
= - 40 m/s
2s
=
- 20 m/s2