# Can You Outrace a Fly in a Car? Investigating the Physics

• ycy88
In summary: And as mentioned, it can't use it's wings to propel itself forward, just like we can't use our arms to do that in a vacuum.No, the fly would start off on the floor and most likely would not hit the window because it wouldn't get off the floor.
ycy88
You are driving a car. A fly is along for the ride (in the car). The fly is not hanging on to anything. Not the window, not the seat. It is flying. If you drive your car fast, faster than the fly to catch up, will the fly hit the back window? Why?

:No. The fly is perched on the *air* - which is accelerated with the car.:

If the air is "accelerated", why won't you feel the "wind" when you are driving in the car?

Because you are accelerated too.

The fly will hit the backwindow if your acceleration is high enough.

DaveC426913 said:
:No. The fly is perched on the *air* - which is accelerated with the car.:

Question:

Wouldn't this depend on whether the windows were open or not? Also, what about inertia?

If the density of the fly is greater than that of the air then he will be moved towards the back window. A helium balloon would move forward in an accellerating car because its density is less than that of the air in the car. My guess is that a fly is denser than air.

What I'm really curious about is how Dave made a post with less than 10 characters?

He posted white text to hide his answer. Select to see.

BicycleTree said:
He posted white text to hide his answer. Select to see.

Oh, very clever. I see limitless possibilities in this!

Huckleberry said:
If the density of the fly is greater than that of the air then he will be moved towards the back window. A helium balloon would move forward in an accellerating car because its density is less than that of the air in the car. My guess is that a fly is denser than air.

What I'm really curious about is how Dave made a post with less than 10 characters?

so the acceleration is simmilar like the one due to gravity isn't it. but if the fly doen't being pull to gravity (acting as same density as air even tough if it don't) would it also smashed to the rear window. i agree with the helium after all

Well, what if it all happen in vacuum? Will the fly smash the rear window? (Assume that you and the fly survive without oxygen)

The fly will won't be able to fly.

ycy88 said:
If the air is "accelerated", why won't you feel the "wind" when you are driving in the car?
The air has very little inertia. It is very easy to accelerate it along with the car. You feel nothing. It *does* have *some* inertia, which is why the helium balloon gets pushed forward as the air gets pushed back.

The fly will hit the backwindow if your acceleration is high enough.
Yep.

Wouldn't this depend on whether the windows were open or not?
That would be a factor, yes.

If the density of the fly is greater than that of the air then he will be moved towards the back window. A helium balloon would move forward in an accellerating car because its density is less than that of the air in the car. My guess is that a fly is denser than air.
Yes, but with so little inertia, the fly is affected more by air resistance. Think of dropping a (non-flying) fly off a roof. It is much mroe affected by air resistance than it is by its own mass. Same thing happens in the car under acceleration.

He posted white text to hide his answer. Select to see. Oh, very clever. I see limitless possibilities in this!
I take no credit. As you peruse this forum, you will see that it is the standard way of providing an answer.

Well, what if it all happen in vacuum? Will the fly smash the rear window? (Assume that you and the fly survive without oxygen) The fly will won't be able to fly.
Ahah! That's clever! But if it were to hop, or use a rocket pack, then yes it would smash into the back window - just as a feather drops like a stone in a vacuum.

DaveC426913 said:
Ahah! That's clever! But if it were to hop, or use a rocket pack, then yes it would smash into the back window - just as a feather drops like a stone in a vacuum.

In a vacuum, wouldn't the fly hit the back window very easily? There is no air to keep the fly accelerated... nothing pushing the fly forward. And as mentioned, it can't use it's wings to propel itself forward, just like we can't use our arms to do that in a vacuum.

What about with gravity? Does that mean the fly starts on the floor and most likely would not hit the window because it wouldn't get off the floor?

Rahmuss said:
In a vacuum, wouldn't the fly hit the back window very easily? There is no air to keep the fly accelerated... nothing pushing the fly forward. And as mentioned, it can't use it's wings to propel itself forward, just like we can't use our arms to do that in a vacuum.
That *would* be the case if not for...
Rahmuss said:
What about with gravity? Does that mean the fly starts on the floor and most likely would not hit the window because it wouldn't get off the floor?
Correct.10char

## 1. Can a fly actually keep up with a car?

No, a fly cannot keep up with a car. A car's average speed is much faster than a fly's maximum flying speed. The fastest fly species can only fly at a speed of about 15 miles per hour, while the average car can travel at speeds of 60 miles per hour or more.

## 2. How does the size of the fly impact its ability to keep up with a car?

The size of the fly does play a role in its ability to keep up with a car. Smaller flies have a harder time flying at faster speeds and may not be able to keep up with a car's speed. However, larger flies, such as horseflies, may be able to keep up with a car for shorter distances due to their larger wingspan and stronger flying abilities.

## 3. What is the main factor that affects a fly's ability to keep up with a car?

The main factor that affects a fly's ability to keep up with a car is air resistance. As the car moves forward, it creates a large amount of air resistance that makes it difficult for a fly to fly against. This makes it nearly impossible for a fly to keep up with a car over long distances.

## 4. How does the speed of the car impact the fly's ability to keep up?

The speed of the car has a significant impact on the fly's ability to keep up. The faster the car moves, the stronger the air resistance it creates, making it harder for the fly to fly against. This means that the faster the car goes, the more difficult it is for the fly to keep up.

## 5. Is it possible for a fly to outpace a car?

No, it is not possible for a fly to outpace a car. Even with favorable wind conditions and a tailwind pushing the fly forward, the car's speed will still be too great for the fly to keep up with for an extended period of time. The fly may be able to briefly match the car's speed, but it will eventually tire out and fall behind.

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