1. Chapter 2 Motion

2. 11.1 Distance and Displacement
What is needed to describe motion completely?
How are distance and displacement different?
How do you add displacements?

3. 11.1 Distance and Displacement I can determine an appropriate frame of reference and decide if an object is moving
How do we know an object is moving?
Frame of reference
Motion is always
relative (compared
to) something
That something is called the
Frame of Reference
for us usually the earth)

4. 11.1 Distance and Displacement I can determine an appropriate frame of reference and decide if an object is moving
How do we know an object is moving?
Frame of reference
We choose a frame that makes sense.
Using the ground as a
frame, the ball is moving
forward
Using the truck as a frame
of reference, the ball goes
up then back down

5. 11.1 Distance and Displacement I can explain the difference between distance and displacement
Distance – the length of a path between two points
Displacement – straight line distance (and direction) between the start and end
Example: Travel 3.5 miles south

6. 11.1 Distance and Displacement I can add one dimensional vectors for displacement, velocity, and acceleration
Adding Displacements (vector addition)
Vector – has number value and direction
If the vectors aren’t in a straight line, then we have to use trigonometry to add the vectors
PHET Vector Addition

7. 11.2 Speed and Velocity
How are instantaneous speed and average speed different?
How can you find the speed from a distance-time graph?
How are speed and velocity different?
How do velocities add?

8. 11.2 Speed and Velocity I can calculate the average speed for a moving object.
Speed – ratio of distance to time
Measured in meters per second (m/s)
Average Speed
Example: A car travels 25 km in 0.2 hours, then 45 km in 0.3 hours. What is the average speed?
Total distance and then total distance
SR-71 Blackbird
Speed: 2070 mph
or 920 m/s

9. 11.2 Speed and Velocity I can calculate the average speed for a moving object.
Practice: A person jog 400 meters in 192 seconds, then 200 meters in 132 seconds, and finally 100 meters in 96 seconds. What is the joggers speed?

10. 11.2 Speed and Velocity I can calculate the average speed for a moving object.
Practice: A train travels 190 kilometers in 3.0 hours, and then 120 kilometers in 2.0 hours. What is its average speed?

11. 11.2 Speed and Velocity I can calculate the average speed for a moving object.
A speedometer does not measure average speed, it measures instantaneous speed.

12. 11.2 Speed and Velocity I can calculate speed from a distance time graph.
A distance time graph can be used to determine speed.
The slope of the graph (distance divided by time) is average speed
Gizmo
Distance vs. Time

13. 11.2 Speed and Velocity I can list two ways velocity changes and show these changes by graphs or diagrams.
Velocity – speed in a direction (vector)
Velocity changes with either
A change in speed
A change in direction
Velocity is added by vector
addition (like
displacement)

14. 11.3 Acceleration How are changes in velocity described?
How can you calculate acceleration?
How does a speed-time graph indicate acceleration?
What is instantaneous acceleration?

15. 11.3 Acceleration I can define acceleration.
Acceleration is a change in velocity, so
Change in speed
Either getting faster
Or getting slower
Change in direction
Turning
Measured in meters per
second squared (m/s2)

16. 11.3 Acceleration I can calculate the acceleration for an object changing speed.
Calculating Acceleration – divide the change in velocity (speed) by the total time
Example: A ball rolls down a ramp, starting from rest. 4 seconds later, it’s velocity is 13 m/s. What is the acceleration of the ball?
First, what is the initial velocity?
0 m/s

17. 11.3 Acceleration I can calculate the acceleration for an object changing speed.
Practice Problem 1
A car traveling at 10 m/s
slows down to 3 m/s in
20 seconds. What is the
acceleration?

18. 11.3 Acceleration I can calculate the acceleration for an object changing speed.
Practice Problem 2
An airplane travels down a runway for 4.0 seconds with an
acceleration of
9.0 m/s2. What is its
change in velocity
during this time?

19. 11.3 Acceleration I can determine acceleration from a speed-time graph.
Reading a Speed-Time graph
The slope of the graph (rise over run) is the acceleration
Straight upward – positive constant acceleration
Straight downward – negative constant acceleration (slowing down)
Flat – constant speed, no acceleration
Curved – changing acceleration

20. How does gravity cause acceleration?
11.4 Free Fall
How does gravity cause acceleration?

21. 11.4 Free Fall I can calculate using the acceleration due to gravity.
Free Fall – when an object is falling under only the influence of gravity
The acceleration due to gravity on the surface of the earth is 9.80 m/s2
So our acceleration equation becomes
Everything else is the same

22. 11.4 Free Fall I can calculate using the acceleration due to gravity.
Problem 1
How fast will a rock dropped
from the top of the empire
state building be going
after 8.0 seconds?