Motion and Forces
Lesson 1: Position and Motion
Position
Position describes the location of an
object. A reference point is a location
to which you compare other locations.
When you describe a position by
comparing it to the location of another
object or place, you are using a
reference point.
Location
Describe Waldo's position?
Location
Describe Waldo's position
in reference to the sailboat.
Motion
Motion is a change in position relative to a
reference point.
Position, Motion, Reference
Imagine you
are flying in
an airplane....
Position, Motion, Reference
Describe the position of the pilot relative to where you are
sitting?
Position, Motion, Reference
Describe the position of the pilot relative to where you are
sitting?



In front of me
15 rows ahead of me
In the front of the aircraft

Others.....
Position, Motion, Reference
Is the pilot in motion relative to where you are
sitting?
Position, Motion, Reference
Is the pilot in motion relative to where you are sitting?
No, the pilot's position is not changing
relative to where I am sitting (always in
the same spot).
Position, Motion, Reference
If I throw a ball to the pilot, is the ball in motion relative to
where you are sitting?
Position, Motion, Reference
If I throw a ball to the pilot, is the ball in motion relative to
where you are sitting?
Yes, the ball is moving from my position
to the pilots position.
Position, Motion, Reference
Is the pilot, the ball, or yourself in motion relative to someone
on the ground?
Position, Motion, Reference
Is the pilot, the ball, or yourself in motion relative to someone
on the ground?
All three are in motion relative to
someone on the ground.
Speed
The speed of an object is a measure of how far something
moves in a given amount of time (how quickly something
changes position).
EXAMPLE:
Two cars traveling at different speeds.....
- Would travel the same distance when both go from Dunlap to Chicago,
but the faster car would arrive sooner.
- Would travel different distances if they both drove for one hour.
Average Speed
Average speed is a way to calculate the speed of an object
that may not always be moving at a constant speed.
When traveling to Chicago, the speed limit may change,
therefore the cars speed will change.....
Cars Speed
Average Speed
Time
Distance Time Graphs
• How
is average speed calculated?
– Speed can be calculated by dividing the
distance an object travels by the time it takes
to cover that distance
– Speed = Distance / Time
• Standard unit for speed is meters per
second (m/s)
Distance Time Graphs
• Used to plot the distance an object travels over time
• The distance of an object away from a reference point is plotted
on the y axis. Time is plotted on the x-axis.
Distance
Time
Distance Time Graphs
• Imagine two friends racing their bikes against each other. Each
start from a stop and race 100 meters down the track. Friend 1 wins
the race in a time of 8 seconds while Friend 2 had a time of 11
seconds.
• Create a distance time graph for each Friend in the race (on the
same plot)
Distance Time Graphs
Starting Line
Finish Line
Friend 1
Distance = 0 meters
Time = 0 seconds
Distance = 100 meters
Time = 8 seconds
Friend 2
Distance = 0 meters
Time = 0 seconds
Distance = 100 meters
Time = 11 seconds
100
Distance
(m)
50
0
0
1
2
3
4
5
6
7
8
Time (s)
9
10
11
12
13
Distance Time Graphs
Starting Line
Friend 1
Distance = 0 meters
Time = 0 seconds
Distance = 100 meters
Time = 8 seconds
Friend 2
Distance = 0 meters
Time = 0 seconds
Distance = 100 meters
Time = 11 seconds
100
Distance
(m)
Finish Line
50
0
0
1
2
3
4
5
6
7
8
Time (s)
9
10
11
12
13
Distance Time Graphs
100
Distance
(m)
Friend 1
Friend 2
50
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Time (s)
• Just from looking at the graph alone, who won the race? How can
you tell?
Distance Time Graphs
100
Distance
(m)
Friend 1
Friend 2
50
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Time (s)
• Just from looking at the graph alone, who won the race? How can
you tell?
– Friend 1 won the race. The line for Friend 1 is steeper (slope is
bigger).
Distance Time Graphs
• The slope, or steepness, of the line is equal to the average speed of
the object
- The faster the object the steeper the line (Friend 1 steeper than Friend 2)
• Average speed can be calculated from the graph by dividing the
change in distance by the change in time for that interval
• Average Speed (Slope) = change in y / change in x
Distance Time Graphs
100
Distance
(m)
Friend 1
Friend 2
50
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Time (s)
Length of y
Length of y
Friend 1
Length of x
100 meters / 8 seconds = 12.5 m/s
Friend 2
Length of x
100 meters / 11 seconds = 9.09
m/s
Velocity
Question: Is there a difference between velocity and speed?
Yes! Velocity is a vector.
• A vector is a quantity that has both size and direction.
• Velocity is a speed in a specific direction.
Examples: 7 m/s south, 5 m/s forward, 2 m/s downward, etc.
Question: Is it possible for two objects to have the same speed but
different velocity's? Why?
Velocity
Question: Is it possible for two objects to have the
same speed but different velocity's? Why?
– Could both be traveling the same speed but in
opposite directions.
– Imagine two bicycles going towards each other
on the sidewalk. Both could be speeding along
at 7 m/s (speed) but they are traveling the
opposite direction (velocity).
Velocity
Imagine riding a elevator to the top floor of a building and back down. Assume the
ride took 5 seconds in each direction and top floor of the building was 10 meters
above the ground. Draw a distance time graph showing the average speed and
another graph showing the average velocity. Remember, velocity includes
direction!
Velocity
Imagine riding a elevator to the top floor of a building and back down. Assume the
ride took 5 seconds in each direction and top floor of the building was 10 meters
above the ground. Draw a distance time graph showing the speed and another
graph showing the average velocity. Remember, velocity includes direction!
Speed
20
20
Total distance
traveled, regardless
of direction
10
Velocity
0
10
Total distance
traveled, including
direction.
Traveling up is
positive, traveling
down is negative
0
0
5
Average speed:
10 meters / 5 s = 2 m/s
10
0
5
10