Question

When we use this laws?

1-when we use this law

`Q=barv*A`

2-when we use this law

`Q=v*A`

Answer 1

1. when flow is turbulent
2. streamline flow of liquids

Explanation:

When liquids are flowing through a pipe of cross sectional area A

then the quantity of fluid crossing per unit time Q can be defined as

Q= v.A

where v is the velocity of liquid particles and A is cross sectional area.

In streamline flow the layers of liquid move without crossing each other's path and if the cross sectional area is decreased the speed

increases suh that volume of liquid is conserved.
when the motion is not streamline the particles reaching the section are not parallel to each other and its value gets a spread as energy is lost in internal collisions ,
therefore

one can use only an average of v i.e. vbar

so the amount of liquid flowing out

Q= vbar.A

however the quantity of fluid flow will be maintained.