1. Acceleration is a vector quantity: This means it has both magnitude (how much) and direction. A car speeding up is accelerating, but so is a car slowing down (negative acceleration, also known as deceleration). A car turning a corner at constant speed is also accelerating because its direction of motion is changing.

2. Acceleration is the rate of change of velocity: It tells you how quickly the velocity of an object is changing. This change in velocity can be in speed, direction, or both.

3. Acceleration is caused by a net force: Newton's second law of motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. This means a larger force will produce a larger acceleration, and a larger mass will result in a smaller acceleration for the same force.