Speed, Velocity, and Acceleration

Speed, Velocity, and Acceleration

Middle School

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Learning Objectives

• Define speed, velocity, and acceleration to describe an object's motion.

• Interpret distance-versus-time graphs to analyze an object's movement.

• Explain how unbalanced forces and mass affect an object's resulting acceleration.

• Understand the importance of a frame of reference when describing motion.

Key Vocabulary

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Speed

Speed is the measure of how fast an object is moving along a path.

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Velocity

Velocity describes an object's speed combined with its specific direction of motion.

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Acceleration

Acceleration is the rate at which an object's velocity changes over a period of time.

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Force

A force is simply a push or a pull acting upon an object.

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Mass

Mass refers to the total amount of matter that is contained within an object.

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Balanced Forces

Balanced forces are when the total net force acting on an object equals zero.

Key Vocabulary

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Unbalanced Forces

When the net force on an object is not zero, the forces are considered unbalanced.

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Net Force

The net force is the sum of all the individual forces that are acting on an object.

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Frame of Reference

A frame of reference is a point of view from which motion is described and measured.

Calculating Speed

• Speed is the distance an object moves over a certain amount of time.

• Instantaneous speed is the speed at one specific moment.

• Average speed is the total distance divided by the total time.

Multiple Choice

What is the definition of speed?

• The distance an object travels over a certain amount of time.

• The speed of an object in a specific direction.

• The rate at which an object changes its speed.

• The total path an object has taken.

Multiple Choice

What is the primary difference between average speed and instantaneous speed?

• Average speed is always faster than instantaneous speed.

• Instantaneous speed is the total distance traveled, while average speed is the total time taken.

• Average speed is the speed over a total duration, while instantaneous speed is the speed at a single moment.

• Only average speed is calculated using distance, while instantaneous speed is calculated using time.

Multiple Choice

A car is driven 200 miles to a different city. The driver speeds up on the highway and slows down in towns. How would the average speed for the entire trip be calculated?

• By finding the speed on the car's speedometer at the exact halfway point of the trip.

• By dividing the total distance of the trip by the total time the trip took.

• By using the fastest speed the car traveled during the trip.

• By adding the fastest and slowest speeds together and dividing by two.

Graphing Speed

• A distance-versus-time graph is used to plot an object's motion.

• The slope of the line on the graph represents the object's speed.

• A steeper slope means a greater speed.

Multiple Choice

What is the primary use of a distance-versus-time graph?

• To measure an object's mass

• To plot an object's motion

• To calculate an object's acceleration

• To show the forces acting on an object

Multiple Choice

On a distance-versus-time graph, what does the slope of the line represent?

• The distance the object has traveled

• The acceleration of the object

• The speed of the object

• The time the object has been in motion

Multiple Choice

If a distance-versus-time graph shows two lines, how can you determine which object is moving faster?

• The object with the steeper slope has traveled a shorter distance.

• The object with the steeper slope is moving at a greater speed.

• The object with the steeper slope has been moving for a longer time.

• The object with the steeper slope is slowing down.

Velocity and Acceleration

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What is Velocity?

• ​Velocity describes an object's motion with both its speed and direction.

• ​A storm moving 25 km/h eastward is an example of velocity.

• ​If an object changes direction, its velocity will also change.

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What is Acceleration?

• ​Acceleration is the rate at which an object's velocity changes over time.

• ​This means an object is accelerating if its speed or direction changes.

• ​Even with constant speed, changing direction means the object is accelerating.

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Types of Acceleration

• ​An object can accelerate by increasing its speed, also called speeding up.

• ​It can also accelerate by decreasing its speed, also called slowing down.

• ​A simple change in the direction of motion is also acceleration.

Multiple Choice

What is acceleration?

• The rate of change of an object's velocity.

• The constant speed of an object in motion.

• The distance an object travels over time.

• The specific direction an object is moving.

Multiple Choice

According to the definitions of velocity and acceleration, how can an object accelerate if its speed remains constant?

• By changing its direction of motion.

• By maintaining a constant velocity.

• By moving in a perfectly straight line.

• By increasing its mass.

Multiple Choice

A race car is driving at a constant speed of 150 km/h around a circular track. Which statement best explains the car's motion?

• The car is accelerating because its direction is constantly changing.

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

• The car's velocity is constant because its speed is not changing.

• The car has a constant velocity and is also accelerating.

How Forces Affect Motion

• A force is a push or pull that can accelerate an object.

• Unbalanced forces cause a change in the object's motion.

• Forces have both a size, measured in Newtons (N), and a direction.

Multiple Choice

What is a force?

• The speed at which an object is moving

• The mass of an object at rest

• A push or pull that can accelerate an object

• The energy an object has due to its position

Multiple Choice

What is the effect of unbalanced forces on an object?

• They cause a change in the object's motion

• They always make an object stop moving

• They only change the direction of an object

• They have no effect on a moving object

Multiple Choice

Which of the following is true about forces?

• Forces have only size, measured in meters (m).

• Forces have only direction, but no size.

• Forces have both size, measured in Newtons (N), and direction.

• Forces can be measured in kilograms (kg) and have no direction.

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Balanced vs. Unbalanced Forces

• For balanced forces, the net force is zero, causing no change in motion.

• An object at rest stays at rest, or moves at a constant velocity.

• For unbalanced forces, the net force is not zero, which causes acceleration.

• The object will speed up, slow down, or change its direction of motion.

Multiple Choice

What is the key difference used to determine if the forces acting on an object are balanced or unbalanced?

• The total net force acting on the object.

• The object's overall mass and weight.

• The direction the object is traveling.

• The speed at which the object is moving.

Multiple Choice

What is the direct result of unbalanced forces acting on an object?

• The object's motion will change.

• The object will maintain a constant speed.

• The object's mass will begin to decrease.

• The object will stop moving.

Multiple Choice

A satellite orbits Earth at a constant speed and a constant altitude. Which statement best describes the forces acting on the satellite?

• The forces acting on it are balanced, resulting in a net force of zero.

• The force from the engine is greater than the force of air resistance.

• The forces acting on it are unbalanced, causing it to maintain its speed.

• There are no forces acting on the object as it moves.

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Force, Mass, and Acceleration

• An object's change in motion depends on its mass and the applied net force.

• Applying a larger force to an object results in a greater acceleration.

• For the same force, an object with greater mass has a smaller acceleration.

• It is harder to accelerate a car than a shopping cart with equal force.

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Multiple Choice

What two factors determine an object's change in motion?

• Its mass and the net force applied to it.

• Its speed and its direction.

• Its size and its shape.

• Its weight and its height from the ground.

Multiple Choice

What is the relationship between the net force applied to an object and its resulting acceleration?

• A larger force results in a greater acceleration.

• A larger force results in a smaller acceleration.

• The force applied has no effect on the acceleration.

• Acceleration depends only on the object's mass.

Multiple Choice

If an equal net force is applied to both a car and a shopping cart, which statement best describes the resulting motion?

• The shopping cart will have a greater acceleration.

• The car will have a greater acceleration.

• Both will have the same acceleration.

• Neither the car nor the cart will accelerate.

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Frame of Reference

• A frame of reference is a set of coordinates for measuring an object's motion.

• On a train, a book appears still to you but moves for an outside observer.

• We must specify the frame of reference to accurately describe an object's motion.

Multiple Choice

What is a frame of reference?

• The point of view for describing motion

• The speed at which an object is traveling

• The distance an object has moved

• The force required to start motion

Multiple Choice

Why can a book on a train seem still to a passenger but appear to be moving to an observer on the platform?

• One person is closer to the book than the other.

• The train is accelerating, changing the book's speed.

• They are observing the book from different frames of reference.

• Only one person is measuring the book's motion accurately.

Multiple Choice

Based on the examples of the book on the train, what is the most important reason for stating the frame of reference when describing motion?

• To prove that motion is only an illusion.

• To ensure measurements of motion are clear and unambiguous.

• To calculate the exact speed of any object.

• To show that an object's mass changes with its speed.

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Common Misconceptions

Misconception	Correction
Acceleration only means speeding up.	Acceleration is any change in velocity, including slowing down or changing direction.
If an object isn't moving, no forces are acting on it.	Forces on a still object are balanced, but they are still present.
An object at a constant speed can't be accelerating.	Changing direction is a form of acceleration, even at a constant speed.

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Summary

• Speed is the distance an object travels over time, while velocity is speed in a specific direction.

• Any change in velocity, such as in speed or direction, is called acceleration.

• An unbalanced force is required to cause a change in an object's motion, making it accelerate.

• The acceleration of an object depends on its mass and the net force applied to it.

Poll

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

• 1 (Not Confident)

• 2 (A Little Confident)

• 3 (Mostly Confident)

• 4 (Very Confident)