1. Acceleration

2. Acceleration
The rate* at which an object’s velocity changes
*rate = a change over time

3. Three types of Acceleration
Positive acceleration
Increase in velocity
Speeding up
Negative acceleration
Decrease in velocity
Slowing down
AKA deceleration
Change in direction
with or without velocity change

4. Is there acceleration?
Discuss with a neighbor whether it is describing acceleration or not
You are riding your bike at 9 km/hr. Ten minutes later, your speed is 6 km/hr
You ride your bike around the block at a constant speed of 11 km/hr
You ride your bike in a straight line at a constant speed of 10 km/hr
You are stopped at a red light and then it turns green

5. Doing the math To find acceleration: A = ∆V t
∆ is the greek letter delta and means “the change in”
To find the change in velocity:
final velocity of the object (Vf) minus initial velocity of the object (Vi)
(also written as Vf – Vi)

6. What’s the unit?
Acceleration is a unit of speed divided by a unit of time
Ex: m/s/s
Can also be written as m/s2
Ex: km/hr/s
Ex: km/hr/hr
Can also be written as km/hr2
What does this unit mean?
It tells you how much velocity is changing per unit of time
Ex: 5 m/s2
Means that velocity is increasing (because it’s a positive #) by 5 m/s every second that the object travels

7. What does it mean?
Ex 2: if a car is accelerating at a rate of 10 m/s/s then its velocity is increasing by 10 m/s every second it is traveling
1s = 10 m/s
2s = 20 m/s
4s = 40 m/s
3s = 30 m/s

8. Some words to look out for
Zero words
Words that either mean the objects starts at rest (not in motion) or stops its motion
Stop
At rest
At a standstill

9. Let’s calculate
A jet starts at rest at the end of a runway and reaches a speed of 80 m/s in 20s. What is its acceleration?
Write what is given:
Vi = 0 m/s (it started at rest)
Vf = 80 m/s
∆t = 20 s
Solve for acceleration:

10. Let’s calculate…again
A skateboarder is moving in a straight line at a speed of 3 m/s and comes to a stop in 2 seconds. What is his acceleration?
Write what is given:
Vi = 3 m/s
Vf = 0 m/s (came to a stop)
∆t = 2 s
Solve for acceleration:

11. Warm up 9/3 (write the prompt then answer)
Write the following numbers/units and label as either: distance, time, mass, speed or velocity
34 mi/hr
29 g
125 m
89 hr
24.5 m/sec west