Vocabulary
What does it mean when an object is "at rest"?
It is not moving.
It's speed is 0.
The equation velocity/time solves for _______.
acceleration
If the slope is negative on a speed-time graph, what does that tell us about the object's acceleration?
Acceleration is decreasing (object is slowing down)
If a skateboarder accelerates from 0m/s to 10m/s in 2s, what is the acceleration?
(10m/s) / 2s = +5m/s2
Time (s) Speed (m/s)
0 0
1 2
2 4
3 6
What is the average acceleration between 0 - 3 s?
(6m/s)/3s = 2 m/s2
What is acceleration?
The change in an object's speed or velocity over time.
How quickly something speeds up or slows down.
displacement/time is the equation for...
velocity
Use the graph on the whiteboard:
What is the acceleration between 3-5 seconds?
0m/s2
A car increases its speed from 30m/s to 50m/s in 2.5 seconds. What is its acceleration?
(50m/s - 30m/s) / 2.5s = (20m/s) / 2.5s = +8 m/s2
Time (s) Speed (m/s)
0 0
1 2
2 6
3 12
Is the acceleration increasing, decreasing, or constant?
Increasing - it goes up by +2m/s then +4m/s then +6m/s.
You are sitting down on a moving train. If the train is your reference point, are you in motion with regards to your reference point?
No.
What is the equation for calculating speed?
distance/time or (df-di) / (tf-ti)
If the line on a speed-time graph is at y=0, what does that tell us about the object's motion?
It is at rest (not moving).
Kirby is flying through outer space when they see a cool looking planet to visit. They slow down from a velocity of 1300m/s to 900m/s in 10 seconds. What is their acceleration?
(900m/s - 1300m/s) / 10s = (-400m/s) / 10s =
-40 m/s2
Time (s) Speed (m/s)
0 0
1 2
2 4
3 6
Is the acceleration increasing, decreasing, or constant?
Constant - the speed increases while the acceleration remains the same
If an object's acceleration is negative, what does that mean for the object's speed?
The object is slowing down. It's speed is decreasing.
What units do we use for acceleration?
m/s/s or m/s2
Use the graph on the whiteboard:
Calculate the acceleration between 0-3 seconds.
(15m/s)/3s = +5 m/s2
A jet ski travels 58 meters in 4 seconds. What is its average acceleration in m/s2?
(Find its velocity. Then, use that to find its acceleration.)
Velocity = 58m/4s = 14.5 m/s
Acceleration = (14.5m/s) / 4s = +3.63 m/s2
Time (s) Speed (m/s)
0 0
3 10
6 28
9 59
What is the acceleration from 6-9 seconds?
(59m/s - 28m/s) / (9s - 6s) = (31m/s) / 3s =
10.33 m/s2
What does it mean for acceleration to be constant?
(Consider the sentence starter: When acceleration is constant, an object's speed is _____.)
When acceleration is constant, an object's speed is increasing by the same amount for each interval of time.
(Example: Every 2 seconds, the speed increases by 3m/s.)
Write out the expanded version of the equation for calculating acceleration.
(vf - vi) / (tf - ti)
Use the graph on the whiteboard:
Calculate the acceleration between 6-8 seconds.
(0m/s - 30m/s) / (8s - 6s) = (-30m/s) / (2s) =
-15m/s2
Miss Adams runs 1600 meters in 12 minutes. What is her average acceleration in m/s2 (rounded to 3 decimal places)?
12 minutes = 720 seconds
speed = 1600m/720s = 2.22m/s
acceleration = (2.22m/s)/720s = 0.003 m/s2
Time (s) Speed (m/s)
0 14
5 18
10 16
15 6
What is the average acceleration from 5-15 seconds?
(6m/s - 18m/s) / (15s - 5s) = (-12m/s) / 10s =
-1.2 m/s2