* A change in speed: The object is speeding up or slowing down.
* A change in direction: The object is changing its direction of motion, even if its speed remains constant.
In other words, any of the following situations indicate acceleration:
* A car speeding up from a stop sign.
* A ball rolling down a hill.
* A car slowing down to a stop at a red light.
* A satellite orbiting the Earth at a constant speed (because it is constantly changing direction).
Key points to remember:
* Acceleration is a vector quantity, meaning it has both magnitude (how much) and direction.
* Acceleration is measured in units of meters per second squared (m/s²).
* Constant velocity means zero acceleration.
* Zero acceleration does not necessarily mean the object is at rest; it can also mean the object is moving at a constant speed in a straight line.
