Albert Teen YOU ARE LEARNING:  What Is Acceleration?  # What Is Acceleration? ### What Is Acceleration?

Acceleration is a change in velocity.

An example of acceleration

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This woman is moving at $3 \space m/s$, so this image tells us the woman's _____________.  2

One second later the woman is moving at $7 m/s$. What happened?  3

In other words, the woman has "accelerated"

Over the course of 1 second, she sped up from $3 \space m/s$ to $7 \space m/s$ Which one of these do you think has the fastest acceleration? Speed and velocity describe how quickly an object travels. What best describes acceleration? How to recognise acceleration

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What type of graph is this?  2

This is a distance - time graph.

It tells you the position of an object at any point in time. 3

What does the gradient of this D-T graph tell us?  4

So the gradient or slope of a D-T graph shows us the velocity the object has. Is this particular object travelling at a constant velocity?  5

So if the speed of this object is not constant, in 1 word what is it doing?  6

So, acceleration is the change in speed or velocity of an object.

This means that a D-T graph with a changing gradient, or a curved line, represents an accelerating object. Acceleration and deceleration

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What is this cyclist doing?  2

Is this cyclist accelerating?  3

The cyclist's acceleration is...  4

So this cyclist has a negative acceleration.

This is the same as saying that this cyclist is decelerating. True or false: Accelerating at $-3 \space m/s^2$ is the same as decelerating at $3 \space m/s^2$ So acceleration can be either positive (speeding up) or negative (slowing down). Do you think you can also talk about both positive and negative deceleration? 1

So an object getting slower and slower has a negative acceleration whereas an object getting faster and faster has a positive acceleration. What does that make acceleration? 2

So, what is the best description of acceleration? Summary!

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Acceleration is how fast the velocity of an object changes

Or its rate of change of velocity. 2

Acceleration can be shown by a curved line on a D-T graph

This image is a good example of an object that is accelerating 3

Acceleration can be both positive and negative

Positive values for acceleration means speeding up, for example $5 \space m/s^2$

Negative values for acceleration means slowing down, for example $-5 \space m/s^2$ 4

You can also use the word "deceleration" for negative acceleration

For example, accelerating at $-5 \space m/s^2$ is the same as decelerating at $5 \space m/s^2$ 5

You cannot have negative values for deceleration

Deceleration always means slowing down, so it doesn't make sense to have both negative and positive values for deceleration. 