Bernoulli's Equation and liquid density

In summary, the difference in pressure, PB – PA, between points B and A can be found by rearranging Bernoulli's Equation and subtracting the two values of pressure obtained for each point using the respective fluid speeds. This method avoids disregarding the constant in the equation and results in a more accurate working.
  • #1
physkid1
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1. The density of the liquid flowing through the horizontal pipe in the drawing is 1200 kg/m3. The speed of the fluid at point A is 7.5 m/s while at point B it is 11 m/s. What is the difference in pressure, PB – PA, between points B and A?
2. Bernoulli's Equation P1 + 1/2 pv1^2 + pgy1 = P2 + 1/2 pv2^2
3. ok to find P is it possible to make P1 = 1/2 pv1^2 + pg (y1 can be neglected) then do the same with P2 then subtract the two values to work out the pressure ? or am i way off ?
 
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  • #2
physkid1 said:
Bernoulli's Equation P1 + 1/2 pv1^2 + pgy1 = P2 + 1/2 pv2^2

to find P is it possible to make P1 = 1/2 pv1^2 + pg (y1 can be neglected) then do the same with P2 then subtract the two values to work out the pressure ?

While you would arrive at the correct final answer, your working would not be quite right.
You would be saying that P1=0.5 p v12 but that's not right. You are disregarding the constant in Bernoulli's Equation; in effect, equating it to zero.

It is better to rearrange Bernoulli's Equation to give the pressure difference, viz., P2 - P1 and that way the constant vanishes and your working will be correct all the way through and no more complicated.
 

1. What is Bernoulli's Equation?

Bernoulli's Equation is a fundamental principle in fluid dynamics that describes the relationship between pressure, velocity, and elevation in a moving fluid. It states that as the velocity of a fluid increases, the pressure decreases, and vice versa.

2. How is Bernoulli's Equation derived?

Bernoulli's Equation is derived from the principle of conservation of energy, which states that the total energy of a system remains constant. In the case of a fluid, this means that the sum of the kinetic energy, potential energy, and internal energy must remain constant as the fluid moves through a tube or pipe.

3. What is the role of liquid density in Bernoulli's Equation?

Liquid density is a crucial factor in Bernoulli's Equation because it affects the potential and kinetic energy of the fluid. The density of a fluid is a measure of its mass per unit volume, and it determines how much potential energy the fluid has due to its elevation and how much kinetic energy it has due to its velocity.

4. How does Bernoulli's Equation relate to the flow of liquids?

Bernoulli's Equation is often used to analyze the flow of liquids, such as in pipes or channels. It helps us understand how changes in pressure, velocity, and elevation affect the flow of a liquid and can be used to predict the behavior of liquids in various situations, such as in pumps or turbines.

5. Can Bernoulli's Equation be applied to all liquids?

Bernoulli's Equation can be applied to all liquids, as long as the flow is steady (i.e., not changing over time) and the effects of viscosity are negligible. However, it is most commonly used for incompressible fluids, such as water or oil, as the equation assumes that the density of the fluid remains constant.

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