Question

A Gipsy car has a canvas top. When the car runs at high speed, the top bulges out. Explain.

Answer 1

The car as stationary and that the wind is blowing around it.  

The Bernoulli's equation is P+ρgh+½ρv² =contant.  

Taking ρ almost constant, in this case, h is also constant. Thus this equation becomes P +½ρv² =constant = k (say)

By Bernoulli's equation, the faster the fluid flow the lower the pressure.  

The static pressure of the atmosphere is felt inside the car, but the increased air speed outside the car causes a pressure drop, and that leads to a pressure differential that causes the bulge.

Thus, air flows from high top low(from down to top) and makes the gipsy car's canvass top to be bulges out.

Answer 2

When Car Runs at high speed, the speed of the air below is less. Thus, Air has the high pressure below, and thus having an low pressure at the top.

These conclusions can be easily made from the Bernoulli's theorem.

P + ρgh + 1/2 ρv² =constant.

Since, density is always constant, and also h is  constant.

Thus this Bernoulli's equation becomes,

     P + 1/2 ρv² = constant =T (Let)

Thus, P = T - 1/2 ρv²

if Velocity increases then pressure decreases and vice versa.

Now, we know that air always flows from the region of high pressure to the region of low pressure.

Low pressure is created at the top due to high velocity, and high pressure is created at the below.

Thus, air flows from high top low(from down to top) and makes the gipsy car's canvass top to be bulges out.

Hope it helps.