Final answer:
An empty plastic bag flies out of a moving car's lowered window due to a decrease in air pressure inside the car as per Bernoulli's principle.
Step-by-step explanation:
When you lower the window on a car that is in motion, an empty plastic bag can sometimes fly out due to decreased air pressure inside the car.
The high velocity of the air flowing over the window creates a region of lower pressure according to Bernoulli's principle, which states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure. The pressure inside the car becomes lower than the atmospheric pressure outside, creating a net force that pushes the bag outward.
This can be observed in other phenomena, like the inward movement of a shower curtain when the water is on, or the sideward force experienced when passing a large vehicle on the highway.
The reason why an empty plastic bag sometimes flies out of a car window when lowered is because of the decreased air pressure inside the car.
When the car is moving, air flows around it creating a lower pressure region inside the car as compared to outside. This pressure difference can cause the bag to be pushed out of the car window.