1. Motion
Chapter 11

2. Measuring Motion
Motion: an objects change in position relative to a reference point.

3. Distance and Displacement
Distance: length of path an object took.
measures how far an object moves along a path.
Displacement: The change in position of an object.
Measures the how far it is between the starting and ending points of the path
Typically shorter than the distance traveled, unless motion is in a straight line.

4. Distance and Displacement
Yellow Line = Distance
Black Line = Displacement

5. Displacement and Direction
Displacement must always indicate the direction the object is moving.
Example:
12 blocks toward school.

6. Speed and Velocity Speed: Velocity:
Describes how fast an object moves.
The distance traveled /time in which motion occurred
Velocity:
Speed of an object in a particular direction.
Speed tells us how fast an object moves. Velocity tells us both speed and the direction that the object moves.
Describe a car moving at constant speed as it rounds a curve. The speed remains constant, but its velocity has changed because the direction in which the car is moving has changed.

7. Calculating Speed SI unit for speed: meters per second (m/s)
To calculate speed, you must measure two quantities: the distance traveled and the time it took to travel that distance.
Average Speed:
SI unit for speed: meters per second (m/s)
Introduce Triangle Method

8. Calculating Speed Equation Gives you… If you know…. v = d/t speed
distance and time
d = v x t
distance
speed and time
t = d/v
time
distance and speed

9. More on Calculating Speed
When an object covers equal distances in equal amounts of time, it is moving at a constant speed.
Instantaneous speed: speed at a given time
Car Speedometer
Ex for constant speed: if a train has a constant speed of 67 m/s, then the train moves a length of 67 m every second.

10. Let’s Practice!!!
Find the velocity in meters per second of a swimmer who swims 110 m toward the shore in 72 s.
Looking for:
Solution:
Given:
Relationship:

11. Let’s Practice!
A train travels 225 kilometers in 2.5 hours. What is the train’s average speed?
Looking for:
Solution:
Given:
Relationship:

12. You Try It!
A person in a kayak paddles down river at an average speed of 10 km/h. After hours, how far has she traveled?

13. Exit Slip
You ride your bike for a distance of 30 km. You travel at a speed of 0.75 km/ minute. How many minutes does this take?

14. Warm-Up
Calculate the distance a plane flies on an 8 hour flight from Chicago to London. Assume a constant speed of 800 km/h.
Looking for:
Solution:
Given:
Relationship:

15. Distance-Time Graphs
Time is always plotted on the X-axis (bottom of the graph).
Distance is always plotted on the Y-axis (side of the graph).

16. Distance-Time Graphs
If an object is not moving, a horizontal line is shown on the distance graph.
Time is increasing to the right, but its distance does not change. We say it is At Rest.

17. Distance-Time Graphs
If an object is moving at a constant speed, it means it has the same increase in distance in a given time.
Time is increasing to the right, and distance is increasing constantly with time. The object moves at a constant speed.
Constant speed is shown by straight lines on a graph.

18. Distance-Time Graphs
Let’s look at two moving objects: Both of the lines in the graph show that each object moved the same distance, but the steeper dashed line got there before the other one:
A steeper line indicates a larger distance moved in a given time. In other words, higher speed.
Both lines are straight, so both speeds are constant.

19. Distance-Time Graphs
Graphs that show acceleration look different from those that show constant speed.
The line on this graph is curving upwards. This shows an increase in speed, since the line is getting steeper:
In other words, in a given time, the distance the object moves is change (getting larger). It is accelerating.

20. Summary
A distance-time graph tells us how far an object has moved with time.
The slope of a distance vs. time graph tells you the speed of an object.
The steeper the graph, the faster the motion.
A horizontal line means the object is not changing its position - it is not moving, it is at rest.
A downward sloping line means the object is returning to the start.

21. Summary

22. Speed-Time Graphs
Speed-Time graphs look much like Distance- Time graphs.
Time is plotted on X-axis
Speed/Velocity is on Y-axis
The slope of a distance vs. time graph is speed.
Slope = Rise/Run

23. Speed-Time Graphs
A straight horizontal line on a speed-time graph means that speed is constant. It is not changing over time.
A straight line does not mean that the object is not moving!!!!

24. Speed-Time Graphs This graph shows increasing speed.
The moving object is accelerating.
This graph shows decreasing speed.
The moving object is decelerating.

25. Speed-Time Graphs
What about comparing two moving objects at the same time?
Both the dashed and solid line show increasing speed.
Both lines reach the same top speed, but the solid one takes longer.
The dashed line shows a greater
acceleration.

26. Summary
A speed - time graph shows us how the speed of a moving object changes with time.
The slope of a speed vs. time graph is acceleration.
The steeper the graph, the greater the acceleration.
A horizontal line means the object is moving at a constant speed.
A downward sloping line means the object is slowing down.

27. Summary

28. Exit Slip
Of the following speed-time graphs, tell me what is happening in each: