* Relative Motion: The fly's speed is relative to its surroundings. If it's resting on your car, it's going the same speed as the car, which is 80 km/h.

* No Movement: From the fly's perspective, it's not moving at all. It's stationary on the car.

So, the fly's speed relative to the car is 0 km/h, but its speed relative to the ground is 80 km/h.