Acceleration

Acceleration

Middle School

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Learning Objectives

Key Vocabulary

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Speed

Speed is the rate at which an object covers a certain distance in a period of time.

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Acceleration

Acceleration is the rate at which an object's velocity changes over time, including changes in speed or direction.

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Gravity

Gravity is the natural force of attraction that exists between any two objects with mass.

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Air Resistance

Air resistance is a type of frictional force that acts upon objects as they move through air.

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Terminal Velocity

Terminal velocity is the constant speed that a freely falling object eventually reaches through the air.

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Force

A force is simply a push or a pull that acts upon an object, causing it to move.

Key Vocabulary

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Mass

The amount of matter that makes up an object. It is a measure of inertia.

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Net Force

The overall force acting on an object when all individual forces are added together.

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Newton's Second Law

What is Speed?

• Speed is a measure of how fast an object is moving.

• Average speed is the distance covered divided by the time taken.

• An object’s speed rarely stays constant and changes over time.

Multiple Choice

What is the definition of speed?

• A measure of how fast an object is moving.

• The direction an object is traveling.

• The total distance an object has traveled.

• The amount of time that has passed.

Multiple Choice

How is the average speed of an object calculated?

• By multiplying the distance traveled by the time taken.

• By dividing the total distance traveled by the time taken.

• By adding the distance and the time together.

• By subtracting the time from the distance traveled.

Multiple Choice

A car travels 20 miles in the first 30 minutes of a trip and then 20 miles in the next 60 minutes. What can be concluded about the car's motion?

• The car's speed was not constant during the trip.

• The car traveled at a constant speed for the entire trip.

• The car's average speed was 40 miles per hour.

• The car must have stopped for 30 minutes.

Introduction to Acceleration

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

• An object speeding up is called positive acceleration.

• An object slowing down is called negative acceleration, or deceleration.

Multiple Choice

What is the definition of acceleration?

• The change of an object's velocity over time.

• The maximum speed an object can reach.

• The distance an object travels in one hour.

• The physical size or mass of an object.

Multiple Choice

What is the key difference between positive and negative acceleration?

• Positive acceleration is speeding up, while negative acceleration is slowing down.

• Positive acceleration only happens in a straight line, while negative acceleration happens on a curve.

• Positive acceleration is for cars, while negative acceleration is for airplanes.

• Positive acceleration is moving up, while negative acceleration is moving down.

Multiple Choice

If a soccer ball is rolling across a grassy field and gradually slows to a stop, which statement best describes its motion?

• The ball experiences negative acceleration.

• The ball experiences positive acceleration.

• The ball's speed remains constant.

• The ball stops accelerating completely.

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Gravity and Falling Objects

Aristotle's View

• ​Aristotle incorrectly thought that heavier objects fall to the ground faster than lighter ones.

• ​​He also believed that all falling objects move downwards at a steady, constant speed.

• ​He described gravity as a force that pulls all objects with mass toward each other.

Galileo's Discovery

• ​Galileo used ramps to slow down and carefully study the effects of gravity on objects.

• ​​His experiments showed that falling objects do not have a constant speed but instead accelerate.

• ​He proved that objects of different masses fall at the same rate, ignoring air resistance.

Multiple Choice

Which statement accurately describes gravity as defined by Aristotle?

• A force that pulls all objects with mass toward each other

• A force that makes heavy objects fall faster than light ones

• A force that causes objects to fall at a constant speed

• A force that only affects objects on ramps

Multiple Choice

How did Galileo's understanding of the motion of falling objects differ from Aristotle's?

• Galileo found that objects accelerate, while Aristotle believed they fall at a constant speed.

• Galileo believed that heavier objects fall faster, while Aristotle believed they fall at the same rate.

• Galileo used ramps to prove that objects have a steady speed, while Aristotle disagreed.

• Galileo showed that air resistance affects all objects equally, while Aristotle focused on mass.

Multiple Choice

Imagine a heavy rock and a light stone are dropped from the same height in a vacuum (a space with no air). Based on Galileo's discoveries, what would be the outcome?

• Both objects would hit the ground at the same time.

• The heavy rock would hit the ground first.

• The light stone would hit the ground first.

• The objects would float instead of falling.

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The Sum of Forces (Net Force)

Unbalanced Forces

• The net force is the sum of all forces, and it is not zero in this case.

• This causes a change in the object's motion, meaning the object will accelerate.

• A falling book speeds up because an unbalanced net force is acting on it.

Balanced Forces

• The net force on an object is zero, meaning all the forces cancel each other out.

• When forces are balanced, the motion of the object does not change at all.

• A book on a table has balanced forces, so it stays in place without moving.

Multiple Choice

What is the 'net force' on an object?

• The sum of all forces acting on an object.

• The force of gravity pulling on an object.

• The speed at which an object is moving.

• The direction an object is traveling.

Multiple Choice

What must be true for an object to accelerate, like a falling book speeding up?

• The net force on the object is zero.

• The net force on the object is not zero.

• The object has no forces acting on it.

• The object is very heavy.

Multiple Choice

A car is traveling on a straight road at a constant speed. Which statement correctly describes the forces acting on the car?

• The forces acting on the car are unbalanced.

• The forces acting on the car are balanced.

• There are no forces acting on the car at all.

• The force of gravity is the only force acting on the car.

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Force, Mass, and Acceleration

Multiple Choice

If the net force on an object is doubled, what happens to its acceleration?

• The acceleration of the object will be cut in half.

• The acceleration of the object will also double.

• The acceleration of the object will not change.

• The acceleration of the object will stop completely.

Multiple Choice

What is the relationship between an object's mass and its acceleration when the same amount of force is applied?

• An object with a larger mass will have a larger acceleration.

• An object with a larger mass will have a smaller acceleration.

• An object's mass has no effect on its acceleration.

• An object's acceleration depends only on the force applied.

Multiple Choice

If you push two carts that have different masses with the same amount of force, what would be the most likely outcome?

• The cart with more mass will accelerate more.

• The cart with less mass will accelerate more.

• Both carts will have the same acceleration.

• Neither cart will accelerate because the force is the same.

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Calculating Acceleration & Terminal Velocity

Acceleration

Terminal Velocity

• ​Air resistance is a type of friction that opposes an object’s downward motion.

• ​​This upward force increases as the object’s speed increases through the air.

• ​When air resistance equals gravity, the object falls at a constant terminal velocity.

Multiple Choice

What is the effect of Earth's gravity on an object in free fall?

• It causes the object's speed to increase every second.

• It causes the object to fall at a constant speed immediately.

• It pushes the object upwards, slowing it down.

• It has no effect on the object's speed.

Multiple Choice

What is the relationship between an object's speed and the force of air resistance acting on it?

• As the object's speed increases, the force of air resistance also increases.

• As the object's speed increases, the force of air resistance decreases.

• An object's speed has no effect on the force of air resistance.

• Air resistance only begins to act when the object stops accelerating.

Multiple Choice

What happens when the upward force of air resistance on a falling object becomes equal to the downward force of gravity?

• The object stops accelerating and falls at a constant speed.

• The object immediately stops moving and hovers in the air.

• The object begins to accelerate at a faster rate.

• The force of gravity becomes stronger than the air resistance.

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Common Misconceptions

Misconception	Correction
Heavier objects always fall faster than lighter objects.	All objects accelerate at the same rate (9.8 m/s2) without air resistance.
Acceleration only means speeding up.	Acceleration is any change in motion, including slowing down or changing direction.
If an object is moving, a net force must be acting on it.	An object at a constant velocity has zero net force.

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Summary

Poll

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

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