2. Motion Motion: when an object changes its position.
Dependent on the reference point.
Reference point: an indicator that orients you; the place from where you measure, record, or witness an event.
Ex. Consider the reference point when describing the motion of a car.
Example notes: From a reference point within the car, the car isn’t moving in relation to you. However, from the street reference point, or a reference point of a building, the car is moving as it passes by.

3. Measuring Motion Distance: (d) how far an object has moved.
Can be measured in m, in, ft, mi, etc.
Displacement: (Δx) distance and direction of an object’s change in position; difference from starting to ending point.
Ex. If a runner runs around a 400 m track and ends where they started, they have traveled a distance of 400 m, but have been displaced 0 m.

4. Example #1 d = 50 + 20 d = ? d = 70 m Δx = ? Δx = 50 – 20
If a soccer player runs after his opponent 50 m North, then turns around and chases him 20 m South, what is his distance and displacement? Use the picture to the right to help you.
d = ?
Δx = ?
d =
d = 70 m
Δx = 50 – 20
Δx = 30 m North
20 m
50 m

5. Sometimes finding displacement isn’t as easy.
Measuring Motion
Sometimes finding displacement isn’t as easy.
If an object travels at a right angle, the Pythagorean theorem is used to find the displacement.
a2 + b2 = c2 b Δx c a
c (the hypotenuse of the right triangle) would be the displacement (Δx)
Note: This will not need to be used every time you find displacement!!

6. Example #2
A delivery truck drives 4 miles West before turning right and driving 6 miles North to make a delivery. Find the delivery truck’s distance and displacement. b Δx c
6 miles a
4 miles
a2 + b2 = c2
= c2
= c2
52 = c2
7.21 = c
a = 4 miles
b = 6 miles
c = Δx = ?
d = 4 + 6
d = 10 mi
c = 7.21
Δx = 7.21 mi Northwest √ √
a2 + b2 = c2

8. Measuring Motion
Speed: (s) the distance an object travels per unit of time.
Can be measured in m/s, mi/hr, ft/min, km/hr, etc. d
s = t

9. Calculating Speed
Example #3: Suppose you ran 2 km in 10 min. With what speed did you run?
s = ?
d = 2 km
t = 10 min
s = 2 km
10 min
s = 0.2 km/min
s = d t

10. Calculating Speed
Example #4: Sound travels at 343 m/s through dry air. If a lightning bolt strikes the ground 2 km away from you, how long will it take for the sound to reach you?
t = ?
s = 343 m/s
d = 2 km
t = 2000 m
343 m/s
1000 m
2000 m =
t = 5.83 s
For a CP (non-honors) group you could skip this problem, but I like to show it to ALL of my students because this would be a great bonus question on a CP test, and a required question for sure on honors.
It makes them take note of LIKE units, refreshes their memory and brings in skills from unit 1 (like metric conversions!), and gets them practicing with rearranging equations. I do NOT let them use the equation triangles or plug in first then rearrange because I want them to get into good habits NOW while the equations are simpler so that they can apply those habits/strategies to harder equations we will get to.
Two things I repeat over and over (until students literally start quoting me):
To rearrange a fraction 1st ALWAYS get it out of a fraction.
Do this by multiplying by the denominator.
1 km
s = d t
(t)
(t)
t s = d s s
t = d s

11. Two Types of Speeds
Average speed: total distance traveled divided by total time traveled.
Ex. If I’m driving to Clemson to watch the National Championship football team play, it is a total distance of 300 miles from my house. If it takes me 5 hours to get there, my average speed is 60 mi/hr.
Instantaneous speed: the speed at any given point – what shows up on your speedometer.
Ex. On my trip to Clemson, at some points on the highway my instantaneous speed is 70 mi/hr. At stoplights, my instantaneous speed is 0 mi/hr.

12. Velocity
Velocity: (v) the speed of an object and the direction of its motion.
Speed can remain constant and velocity change if the object is changing direction.
Calculated the same as speed, just must include direction in your answer!! d
v = t

13. Practice Time
A girl is training to run a 5k (3.1 mile) race. If she runs a trial race in 0.5 hours, what is her average speed?
An elevator at a museum can travel 210 m upwards in 35 s. What is the elevator’s velocity?
How far does a car travel in .75 hrs if it is moving at a constant speed of 45 mi/hr?
If a motorcycle is moving at a constant speed down the highway of 40 km/hr, how long would it take the motorcycle to travel 10 km?
Answer: s = 6.2 mi/hr or 10 km/hr
Answer: v = 6 m/s upwards
I have students work these out in their notes and I walk around and help them as they work. Then we go over the answers all together. I especially encourage CP students that if they don’t know what to do, they at least need to set up the problem (labeling values that they know and writing the appropriate equation.). They should NEVER leave a problem blank!
Answer: d = mi
Answer: t = 0.25 hr

15. Graphs can visually help us to understand an object’s motion.
Graphing Motion
Graphs can visually help us to understand an object’s motion.
Slope: the steepness of a line.
Calculated as rise = Δy
run Δx
On a distance vs. time graph, this means…
Calculated as rise = Δy = distance
run Δx time
Therefore on a distance vs. time graph, the slope = speed.

16. Graphing Motion Describe the motion of each graph.
The object is moving at a constant speed, away from the reference point.
The object is moving at a constant speed, coming towards the reference point.
Honors: You can have them calculate the slope (and therefore the average speed) of the lines on the first two graphs, or at any given point to find instantaneous speed on the last two graphs. I would not do this with CP though!
The object is speeding up, due to the line becoming steeper.
The object is slowing down, due to the line leveling out.

17. Sketch a graph that would show an object not moving.
Graphing Motion
Sketch a graph that would show an object not moving.
Sketch a graph that would show an object moving at a constant speed, stopping, then speeding up.