Imagine a car which is 14 feet long. I have installed an airtight metal pipe along the length of the car. The pipe has a diameter of 12 inches at the front. After 1 foot, i.e at 13 feet, the pipe's diameter is reduced to 2 inches. The rest of the pipe till the end (from 13 feet till end) is now 2 inches in diameter.

Imagine the car is traveling on the highway at a constant speed of 50 miles an hour. I want to calculate the velocity of the air coming out of the rear end of the pipe. There are no impediments inside the pipe. It is a straight pipe. Air is flowing in at the front opening which is 12 inches in diameter and it coming out from the other end where the diameter is 2 inches.

I want to calculate the relationship between the front diameter and the rear diameter and the speed at which the air will be coming out from the ear end. Suppose the front diameter is now 14 inches and the rear diameter is 4 inches, keeping the length of the pipe to be identical, i.e 14 feet.

Because of the reduced diameter, the air coming out will be significantly higher force than the air being sucked into from the front end when the car is moving at a constant speed of 50 miles an hour. There has also to be relationship between the speed at which the car is moving. At lower than 50 miles/hour, say 30 miles/hour, the air coming out of the pipe at the rear end will be at a lower speed as compared at 50 Miles/hour. Similarly, at higher speed, say 90 miles/hour, the air coming out of the pipe at the rear end will be at a much higher speed as compared at 50 Miles/hour. What is that relationship?

## Comments rated to be "almost" Good Answers:

Re: Calculate air speed" by Rixter on 10/18/2015 5:44 PM (score 1)Re: Calculate air speed" by dkwarner on 10/18/2015 11:38 PM (score 1)Re: Calculate air speed" by dkwarner on 10/19/2015 12:00 PM (score 1)