3. Unit 5 Review, Day 2: Acceleration and Velocity-Time Graphs

4. Unit 5: Motion and Forces
LG1: SWBAT define average speed and calculate the average speed of an object.
LG2: SWBAT interpret distance-time graphs.
LG3: SWBAT define acceleration calculate the acceleration of an object.
LG4: SWBAT interpret velocity-time graphs.
LG5: SWBAT define Newton’s first law of motion and use it explain the motion of objects.
LG6: SWBAT define Newton’s second law of motion and use it to explain the motion of objects.
LG7: SWBAT define Newton’s third law of motion and use it to explain the motion of objects.

5. Learning Goal 3: SWBAT define acceleration and calculate the acceleration of an object.

6. Acceleration
Acceleration is a change in velocity divided by the time it takes for the change to happen.
Acceleration can be positive (speeding up) or negative (slowing down).

7. Practice Problems
Jahina is jogging. She speeds up from 2 m/s to 8 m/s in 6 seconds. What is her acceleration?
Quentavia is driving when she sees a stoplight ahead. She slows down from 30 m/s to 10 m/s in 4 seconds. What is her acceleration?
Roterra is running a race. Near the end, she speeds up, increasing her speed from 7 m/s to 13 m/s in 12 seconds. What is her acceleration?
Kris is riding a bike. He slows down from 18 m/s to 9 m/s in 3 seconds. What is his acceleration?

8. Learning Goal 4: SWBAT interpret velocity-time graphs.

9. Velocity-Time Graphs A B C D

10. Interpreting points from v-t graphs
Each point has y-coordinate and x-coordinate.
Y-coordinate tells you the velocity (speed) of the object at that point.
X-coordinate tells you the total time that has passed since object started moving.
Point B: (4, 8)
x = 4 s
y = 8 m/s

11. Practice
At point C, what is the object’s speed, and how much time has passed?
After 2 seconds, what was the object’s speed?
How many seconds did it take for the object to reach a speed of 6 m/s?
At point D, what is the object’s speed? A B C D

12. Calculating acceleration from v-t graphs
To find object’s acceleration during an interval:
Find the change in speed (y2 – y1)
Find the change in time (x2 – x1)
Divide change in speed by change in time

13. Example
Acceleration from point A to point B: A B C D

14. Practice What was the acceleration from O to A?
What was the acceleration from A to B?
What was the acceleration from B to C?
What was the acceleration from D to E?

15. Independent practice time!