I was walking back from lunch with college last week. Not being able to finish what was on my plate I used a take out Container to carry the rest back. The take out container was Styrofoam. (Yes bad for environment )
IIt was an EXTREMELY WINDY day. A gust or wind came by. The top of container snapped open and the food was blown off onto the ground. I still had the container in my hand.
I picked up the food, put into in container, closed lid, held it closed by pressing downward. Dropped it off in a garbage bin (yes food waste resource waste).
My colleague immediately stated the reason for the lid propping open.
What was the reason? TLK, hold your thought for a week.
@Southie Jaisa ki container jab khola jaega tab kuch hawa uske andar enter karegi, ab bernoulli equation k hisab se jaha velocity jyada hai waha pressure kam hoga, yaha bahar jyada velocity hai to bahar kam pressure hai, upward suction milega r khana bahar ayega. Doosra karah yah b ho sakta h k air container wall se bifurcate hogi aur swirl hogi aur andar ka kahana bahar nikalegi jaisa ki gaddo me hota hai, yaha kinetic energy dominate kr rhi hai ya pressure energy nahi kah sakta
@Southie Jaisa ki apne btaya ki food container styrofoam ka h, jo khana garm rakhne k liye upyog kiya jata h, pressure is directly proportional to temperature, to container k andar temp jyada h to pressure b jyada hoga, ab bahar hanlanki pressure kam h phr b container k andar itana b jyada pressure ni hoga k sufficient suction de sake, to ye ni ho sakta, we can rule out this possiblity.
@Southie Par mai "pressure difference (low ambient pressure with respect to pressure inside the container) due to Bernoulli's theorem" ke sath jana pasand karunga, lock kar diya jaye :)
@Southie Jaisa ki container jab khola jaega tab kuch hawa uske andar enter karegi, ab bernoulli equation k hisab se jaha velocity jyada hai waha pressure kam hoga, yaha bahar jyada velocity hai to bahar kam pressure hai, upward suction milega r khana bahar ayega. Doosra karah yah b ho sakta h k air container wall se bifurcate hogi aur swirl hogi aur andar ka kahana bahar nikalegi jaisa ki gaddo me hota hai, yaha kinetic energy dominate kr rhi hai ya pressure energy nahi kah sakta
@Southie Jaisa ki apne btaya ki food container styrofoam ka h, jo khana garm rakhne k liye upyog kiya jata h, pressure is directly proportional to temperature, to container k andar temp jyada h to pressure b jyada hoga, ab bahar hanlanki pressure kam h phr b container k andar itana b jyada pressure ni hoga k sufficient suction de sake, to ye ni ho sakta, we can rule out this possiblity.
Agreed. Especially since food was almost at ambient temperature by that time.
@Southie Par mai "pressure difference (low ambient pressure with respect to pressure inside the container) due to Bernoulli's theorem" ke sath jana pasand karunga, lock kar diya jaye :)
@Southie when air strikes edge of a wall then it gets bifurcated from the top of the wall. Let's say surface of wall is curved, air will flow along the surface, after reaching bottom of the wall it will swirl upward and lift object lying on ground. Assume velocity of air is high enough to take the object with it in upward direction.
Pressure could open the lid but if lid was attached lid would protect the food from low pressure.
If wind attacked from front then its drag , lift effect.
If the lid is completely removeable. Then its pressure difference.
Sounthie need to give more details about container.
Btw southie, I am sure that the lid flipped open because wind got under the lid. It's like you drive your car with the hood unlatched, and just resting on the front panel.
Pressure difference will work when wind is flowing above and under the lid. In your case, it was not
Btw southie, I am sure that the lid flipped open because wind got under the lid. It's like you drive your car with the hood unlatched, and just resting on the front panel.
Pressure difference will work when wind is flowing above and under the lid. In your case, it was not
I am not sure the wind needs to get under the lid. There is already sir inside the box (that is - air present under the lid) This air is probably close to stagnant. So P is 1 armosphere inside the box.
Above the lid, P is lower than 1 atm due to high speed.
So delta p - P inside minus P outside > 0. Hence lid props open?
and that is the case every time, even during the slight breeze (I mean delta p > 0), You dont experience the lid opening phenomena at that time.
Its not delta p > 0, its the velocity of the wind. Its more like how kite goes up, rather than how airplane lifts up.
During slight breeze, the wind speed - the v term - is small enough that delta P is not sufficient to prop the lid open. As Wind speed picks up, the delta p gets larger and larger. Till the force exerted on the lid cover underside is large enough to snap the cover open.
I didn't understand the last sentence about kite vs plane lift.