Eli5: How come flies don’t smash into the back window inside a moving vehicle while they’re flying around? Surely they don’t fly “with” the vehicle.
In: Physics
What happens to a flying fly in a car when you break suddenly?
It’s all about relativity….
The fly moves through the air in the car like a fish moves through water. When a car moves forward, so does the air inside (pushed by the windows, doors, etc.) So the fly doesn’t feel any “relative motion” in the air just because the car moves forward, the same way that a fish would not be slammed against its bowl just because the bowl is moving. The air is considered “at rest” relative to the car. This may change for an instant, during hard acceleration or braking, but in general, the air trapped in the car is not moving relative to the car, only relative to the air outside.
The air is vehicle is moving with the vehicle so the fly just needs to fly *almost* normal.
When accelerating from a stop the air does ‘slosh’ to the back of the vehicle until it equalizes, you can observe this when you have helium balloons because they will come forward towards the windshield during acceleration.
They fly with the air inside the car. Do you feel pushed against the back of the seat when the car is moving at steady speed?
Because the vehicle, and the atmosphere inside of it, are travelling the same speed as the car.
If you put your hand up in a car while going 60 mph, your hand doesn’t fly backwards and snap, it is going the same speed as the rest of the vehicle.
If you were to get in the back of a moving van, and jump in the air, you won’t fly backwards against the wall, you’ll land where you jumped up from
Imagine you’re holding a ball in a moving vehicle. If you throw that ball in the air, it goes straight up relative to you. This is because by holding it, you’ve given it your momentum, your momentum having come from the car. Momentum lasts until something stops it. When a fly takes off in a car, it keeps the momentum of the car. There’s nothing that causes the fly to lose that momentum, so it can just fly and around relative to the car.
>How come flies don’t smash into the back window inside a moving vehicle while they’re flying around? Surely they don’t fly “with” the vehicle.
They do. The same way that your body moves “with” the body of an aircraft.
When you are on a plane, if you drop something in your seat… what happens? It just falls like you would expect it to and lands on your lap or the floor. It isn’t ripped out of your hand at hundreds of miles an hour and slammed into your chest.
The contents of the plane (and the contents of the interior of the car cabin) are moving *relative* to the body of the vehicle, not to the surface of the Earth.
The inside of a moving vehicle is moving at the same speed as the rest of it, friction isn’t what’s keeping you from flying backwards, but rather momentum. Same reason why you end up lurching forwards when you come to a sudden stop.
If a fly is flying in the air inside of a moving vehicle then it’s already moving at however many miles per hour, plus the speed it naturally flys at.
Latest Answers