Final answer:
A car speeding up at a green light is increasing speed, while a car slowing down at a red light is decreasing speed. A car that is turning changes direction, and this is also considered acceleration, even with a constant speed.
Step-by-step explanation:
In physics, a car speeding up at a green light would be increasing speed. When a car slows down at a red light, it would be decreasing speed. Moreover, a car turning would change direction, and is still accelerating, even if the speed is constant. This is because acceleration is defined as a change in velocity, and since velocity is a vector that includes both speed and direction, any change in direction is a form of acceleration.
The concept of instantaneous speed, which a speedometer shows, is different from average speed over a longer period. Understanding how acceleration can occur—even at a constant speed when direction changes—is crucial for comprehending the full nature of motion in physics.