* Change in speed: If the object speeds up or slows down.
* Change in direction: Even if the object's speed remains constant, if it changes direction, it's accelerating.
Examples:
* A car speeding up from a stoplight: The car is accelerating because its speed is increasing.
* A ball thrown straight up in the air: The ball accelerates both on the way up (slowing down) and on the way down (speeding up).
* A car turning a corner at a constant speed: The car is accelerating because its direction is changing.
* The Earth orbiting the sun: The Earth is constantly accelerating because its direction is constantly changing.
Key points:
* Acceleration is a vector quantity: It has both magnitude (how much) and direction.
* Constant speed does not mean no acceleration: If the direction changes, the object is still accelerating.
* Zero acceleration means constant velocity: If the object is not accelerating, its speed and direction remain constant.
