1. Describing and Measuring Motion
Section 1

2. Reference Point
In order to observe an object in motion you must observe the object in relation to another object that appears to stay in the same place.
Common reference points:
Earth’s Surface
Buildings
Trees
Mountains

3. Speed Speed: the distance an object travels in one unit of time
Common units:
Time- seconds, minutes and hours.
Distance- meters, kilometers and centimeters.
Formula:
Speed = Distance
Time
SI unit for speed is meters per second (m/s)

4. Try it out…
If you walk for 1.5 hours and travel 7.5 km, what is your speed?
S= D T
S= 7.5 km
1.5 hrs
S= 5 km/h

5. Average Speed
Since objects do not travel at a constant speed the average speed is usually calculated.
Formula:
Average speed= Total Distance (m)
Total Time (s)

6. Try it out…
A car travels 30 km in the first 30 minutes of a trip and 20 km in the second 30 minutes, what is the average speed the car travels?
Average speed = total distance
total time
Average speed = 50km
60min
Average speed = .83 km/min

7. Instantaneous Speed
The rate at which an object is moving at a given instant in time.

8. Velocity Velocity is the speed of an object in a particular direction.
The only difference from speed is that velocity includes direction.
Which of the following is an example(s) of velocity?
a. 25 m/s forward c. 55 m/h south
b. 1,500 km/h d. all of the above.

9. Acceleration
Section 2

10. Acceleration Acceleration is the rate at which velocity changes.
Acceleration is not just how much velocity changes. It is also how fast velocity changes.

11. Acceleration
Since velocity involves both speed and direction acceleration refers to:
Increasing speed- running to catch a bus, throwing a baseball etc.
Decreasing speed- a car coming to a red light. Sometimes this is called deceleration.
Changing direction- a car changing lanes or going around a curve.
Can a car driving at constant speed be accelerating?

12. Calculating Acceleration
Acceleration= final velocity- initial velocity
Time
It is expressed in m/s/s or m/s2
Suppose you get on your bicycle and accelerate southward at a rate of 1 m/s/s.
This means that every second, your southward velocity increased by 1m/s.

13. Try it out…
A roller coaster rapidly picks up speed as it rolls down a slope. As it starts down the slope its speed is 4 m/s. But 3 seconds later, at the bottom of the slope, its speed is 22 m/s. What is its average acceleration?

14. Show your work! Acceleration = Final Velocity – Initial Velocity Time
Acceleration = 22m/s - 4 m/s
3 sec.
Acceleration = 18 m/s
Acceleration = 6 m/s2
Acceleration is measured in m/s2 or m/s/s