Yes, when an object speeds up or slows down, its speed is definitively changing.
When we talk about an object speeding up, it means its velocity is increasing over time. Conversely, when an object is slowing down, its velocity is decreasing over time. In both these scenarios, the magnitude of the object's velocity, which is its speed, is undergoing a transformation.
Understanding the Change in Speed
Think about your car's speedometer.
- If the needle is moving from 30 mph to 40 mph, you are speeding up, and your speed is changing.
- If the needle is moving from 50 mph to 20 mph, you are slowing down, and your speed is changing.
The very definitions of "speeding up" and "slowing down" are centered around the concept of speed increasing or decreasing, respectively.
Speed Change and Acceleration
According to the provided reference, speeding up and slowing down are directly linked to a fundamental concept in physics: acceleration.
When an object speeds up, slows down, or changes direction, it is undergoing acceleration.
This statement highlights that a change in speed is a form of acceleration. While acceleration is more broadly defined as the rate of change of velocity (which includes changes in direction as well as speed), the acts of speeding up and slowing down specifically involve changing the magnitude of velocity.
What is Acceleration?
Acceleration is the rate at which an object's velocity changes over time. Velocity is a vector, meaning it has both magnitude (speed) and direction.
- Speeding Up: The object accelerates in the same direction as its motion.
- Slowing Down: The object accelerates in the opposite direction of its motion (often called deceleration, but it's a form of acceleration).
Therefore, if an object is speeding up or slowing down, its velocity is changing, and specifically, its speed is changing. This change in velocity is what is defined as acceleration.
Practical Examples
Consider these everyday situations:
- Launching a Rocket: As it ascends, its speed increases rapidly. It's speeding up and accelerating.
- Applying Brakes: When a car brakes, its speed decreases until it stops. It's slowing down and undergoing acceleration (in the opposite direction of motion).
- A Ball Thrown Upward: As it rises, it slows down until it reaches its peak. Its speed is changing.
- A Ball Falling Downward: As it falls (ignoring air resistance initially), it speeds up. Its speed is changing.
In each case, a change in speed is evident, which corresponds to the object undergoing acceleration.
Summary of Concepts
| Action | Effect on Speed | Related to Acceleration? |
|---|---|---|
| Speeding Up | Increases | Yes |
| Slowing Down | Decreases | Yes |
| Changing Direction (constant speed) | Stays the same | Yes |
As the table and the reference indicate, speeding up and slowing down are specific types of acceleration where the speed (the magnitude of velocity) is actively changing.
In conclusion, the statement is correct: when an object speeds up or slows down, its speed is indeed changing.
