1. Chapter 2: Motion Section 1: Describing Motion

2. What is Motion? What is motion?
How can we tell if something has moved or is moving?

3. Motion
Motion occurs when an object changes position relative to a certain point
Whenever an object moves, we compare that object to something in the background that is assumed to be not moving. The background is your frame of reference.
Frame of Reference Animation
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4. Describing Motion Motion can be described using the following:
Distance
Displacement
Speed
Velocity

5. Distance vs. Displacement
Distance –how far an object has moved
Measured in base units of meters
Other Metric units: kilometers, centimeters, millimeters, etc.
Other English units: feet, miles, inches, etc.
Displacement – how far an object has moved from the starting point and the direction of the movement relative to the starting point
Values should have units of length and a direction
What is the runner’s distance travelled?
What is the runner’s displacement?

6. SPEED vs. Velocity
Speed–the distance an object travels in a given amount of time
Objects usually do not travel at a constant speed so we use average speed to describe the motion of the object.
Instantaneous speed is the speed of an object at a given point in time. (Speedometers measure instantaneous speed!)
Values should include a unit of length per unit of time
i.e. 20 meters/second
Velocity– the displacement of an object in a given amount of time
Values should include a unit of length per unit of time and a direction
i.e. 20 meters/second north

7. Calculating Average Speed
Speed is the rate of an object’s change in position
A rate is any change over time
To calculate average speed (s), you divide the total distance travelled (d) by the total time (t) it took to travel that distance
avg. speed = 𝐝𝐢𝐬𝐭𝐚𝐧𝐜𝐞 𝐭𝐢𝐦𝐞
Because speed is a rate, the units should always have two parts: units of length over units of time
i.e. meters per second (m/s), miles per hour (mi/hr)

8. Speed Problems
For each problem:
List the givens
List the formula you will use
Write the givens in your formula, including units
Show all math calculations
List appropriate units on your final answer
If a plane traveled 1760m in 8 seconds, what was its average speed?

9. Speed Problems
For each problem:
List the givens
List the formula you will use
Write the givens in your formula, including units
Show all math calculations
List appropriate units on your final answer
2. If a car takes 25 seconds to travel 750 meters, what was its average speed?

10. Speed Problems
For each problem:
List the givens
List the formula you will use
Write the givens in your formula, including units
Show all math calculations
List appropriate units on your final answer
3. It takes you 15 minutes to walk to the grocery store; If you walk at an average speed of 4 miles/hour, how far away is it?

11. Speed Problems
For each problem:
List the givens
List the formula you will use
Write the givens in your formula, including units
Show all math calculations
List appropriate units on your final answer
4. A cruise ship is traveling at an average rate of 50km/hr. How long does it take to go 700 km?

12. Distance- Time Graphs
Distance-time graphs show the motion of an object over a certain period of time
X-axis: Time
Y-axis: Distance
We can use the slope (rise over run) of the line to determine the speed of the object
A straight line indicates constant speed
A horizontal line indicates that the object is not moving
A curved line indicates changing speed

13. Distance- Time Graphs Practice
1. At which section(s) on the graph does the object have a constant speed? 2. At which section(s) on the graph does the object have a changing speed? 3. At which section(s) on the graph is the object stopped? 4. What is the average speed of the object for section “a”? 5. What is the total distance the object travelled?