Acceleration

Acceleration

Middle School

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Learning Objectives

Key Vocabulary

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Acceleration

The rate at which velocity changes, which can be a change in speed, direction, or both.

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Velocity

A measure of an object's speed and its specific direction of motion, making it a vector quantity.

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Vector

A measurement, like velocity or acceleration, that has both size (magnitude) and direction.

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Deceleration

This is negative acceleration, which means an object is slowing down or its speed is decreasing.

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What is Acceleration?

• Acceleration is the rate of change of an object's velocity.

• Velocity describes an object's speed and its direction of motion.

• This means acceleration can be speeding up, slowing down, or changing direction.

• Both acceleration and velocity are vectors, having size and direction.

Multiple Choice

According to the definition provided, which of the following is NOT a change in velocity?

• A car maintaining the same speed and same direction.

• A car speeding up on a straight road.

• A car slowing down for a stop sign.

• A car turning a corner at a constant speed.

Three Ways an Object Can Accelerate

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Increasing Speed

• This is often called positive acceleration by many scientists.

• It happens when an object's velocity increases over time.

• A rocket launching into space is a perfect example.

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Decreasing Speed

• This is also known as deceleration or negative acceleration.

• It occurs when an object's velocity decreases over time.

• A car using its brakes to stop is an example.

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Changing Direction

• An object accelerates even if its speed stays constant.

• This happens when the object’s direction of motion changes.

• A person on a moving carousel is always accelerating.

Multiple Choice

A Ferris wheel moves at a constant speed. Why is a person riding it considered to be accelerating?

• Because they are constantly changing direction.

• Because their speed is increasing.

• Because their speed is decreasing.

• Because they are not actually accelerating.

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Calculating Acceleration

• To calculate an object's acceleration, you measure the change in its velocity over time.

• The formula is: Acceleration = (Final Velocity - Starting Velocity) / Time.

• The standard unit for acceleration is meters per second squared, written as m/s².

• For example, a skater's acceleration is (4 m/s - 0 m/s) / 2.5 s = 1.6 m/s².

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Multiple Choice

A roller coaster accelerates from an initial speed of 6.0 m/s to a final speed of 70 m/s over 4 seconds. What is its acceleration?

• 16 m/s²

• 19 m/s²

• 76 m/s²

• 256 m/s²

Graphing Acceleration

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Positive Acceleration

• ​A straight line slanting upward shows positive acceleration.

• ​​The object's speed increases at a steady and consistent rate.

• ​This is commonly referred to as the object speeding up.

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Negative Acceleration

• ​A straight line slanting downward shows negative acceleration.

• ​​The object's speed decreases at a steady and consistent rate.

• ​This is also called deceleration or simply slowing down.

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Zero Acceleration

• ​A flat, horizontal line on the graph shows zero acceleration.

• ​​This means the speed of the object remains constant over time.

• ​The object moves at a steady speed without any acceleration.

Multiple Choice

On a speed-time graph, what does a flat, horizontal line away from the x-axis represent?

• Constant speed (zero acceleration)

• Constant positive acceleration

• Constant negative acceleration

• The object is at rest

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Common Misconceptions

Misconception	Correction
Acceleration only means speeding up.	Acceleration is any change in velocity: speeding up, slowing down, or changing direction.
An object at a constant speed cannot be accelerating.	An object at a constant speed accelerates if its direction is changing.

Multiple Choice

What is the primary difference between velocity and acceleration?

• Velocity is the rate of change of acceleration, while acceleration is speed in a direction.

• Velocity is the speed and direction of an object, while acceleration is the rate at which that velocity changes.

• Velocity and acceleration are the same thing and both measure how fast an object is going.

• Velocity is measured in m/s², while acceleration is measured in m/s.

Multiple Choice

A racecar drives around a circular track at a constant speed of 100 mph. Why is the car accelerating?

• Because its direction is constantly changing.

• Because 100 mph is very fast.

• Because the car's speed is increasing.

• The car is not accelerating because its speed is constant.

Multiple Choice

A dog running at 7.5 m/s slides to a complete stop on a slippery floor in 15 seconds. What is the dog's acceleration?

• -0.5 m/s²

• 0.5 m/s²

• -2.0 m/s²

• 7.5 m/s²

Multiple Choice

Imagine a speed-time graph with a line that starts at the origin, slants upward to a point, then becomes a horizontal line for a few seconds. What motion does this graph describe?

• The object speeds up and then maintains a constant speed.

• The object is at rest and then starts moving at a constant speed.

• The object speeds up and then slows down.

• The object maintains a constant speed and then stops.

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Summary

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

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• 3

• 4