What is acceleration If youre traveling in a car at a constant speed of 50 mph are you accelerating No youre not Acceleration is the rate of change of velocity Acceleration In order for acceleration to occur velocity MUST be ID: 778694
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Slide1
Acceleration
Slide2Acceleration
What is acceleration?
If you’re traveling in a car at a constant speed of 50 mph, are you accelerating?
No, you’re not. Acceleration is the rate of change of velocity.
Slide3Acceleration
In order for acceleration to occur, velocity MUST be
changing
.
Remember, velocity is the speed
and
direction an object is traveling.
In order for acceleration to occur, something must be
speeding up
,
slowing down
or
changing direction
.
Slide4Types of Acceleration
If a car is speeding up, does it have positive or negative acceleration?
Positive
If a car is slowing down, does it have positive or negative acceleration?
Negative
If a car is traveling at a constant speed of 50 mph, does it have positive or negative acceleration?Neither! It’s acceleration is 0. (Technically, zero is a positive number, but we won’t get into that.)
Slide5Speed/Time Graphs
This graph shows speed increasing over time.
Would the acceleration be positive or negative?
This graph shows positive acceleration.
Time
Speed
Slide6Slopes of Speed/Time Graphs
When the line on a graph goes upward from left to right, it is said to have a
positive
slope. A
positive
slope on a speed/time graph shows positive acceleration. TimeSpeed
Slide7Speed/Time Graphs
What does this graph show?
As time is going by, how is the speed changing?
If the speed is decreasing over time, is the acceleration positive or negative?
This speed/time graph shows negative acceleration.
TimeSpeed
Slide8Slopes of Speed/Time Graphs
When the line on a graph goes downward from left to right, it is said to have a
negative
slope.A negative
slope on a speed/time graph shows a
negative acceleration.TimeSpeed
Slide9Speed/Time Graphs
What does this graph show?
As time is going by, the speed is staying the same.
Is the object accelerating if the speed stays the same?No! This graph shows no acceleration. It is possible for an object to have speed with no acceleration.
Time
Speed
Slide10Slopes of Speed/Time Graphs
When the line on a graph is perfectly horizontal, it’s slope is said to be
zero
.A zero slope on a speed/time graph shows
zero
acceleration.TimeSpeed
Slide11Calculating Acceleration
Acceleration is often given with the units m/s ²
With these units, acceleration is telling us how many m/s faster (or slower) an object is moving each second.
The equation for acceleration is…
Acceleration = (final velocity – initial velocity) / time
Slide12Calculating Acceleration
A car is sitting a red light when the light turns green. The car goes. After 10 seconds the car is traveling at a speed of 20 m/s. What is the car’s acceleration?
A = (20 – 0) / 10 = 2 m/s²
That means each second that passed the car was traveling 2 m/s faster than the previous second.
This is an example of calculating positive acceleration.
Slide13Calculating Acceleration
A car is traveling at a speed of 50 m/s. The driver notices a cop car and slows to a speed of 30 m/s over a period of 5 seconds. What is the car’s acceleration?
A = (30 – 50)/ 5 = -4 m/s²
Slide14Reading a Speed/Time Graph
Give an explanation for what might be occurring if a car’s speed/time graph looked like this…
Time
Speed
Slide15Reading a Speed/Time Graph
Here is another speed/time graph.
The car accelerates twice. Which portions of the graph show the car accelerating?
Time
Speed
When does the car have a greater acceleration? How do you know?
The steeper the slope the greater the acceleration.
Slide16Reading a Speed/Time Graph
‘Read’ the following speed/time graph. Be as descriptive as possible.
Time
Speed