Calculate Time to Fill Bathtub with Volume Flow Rate

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Discussion Overview

The discussion revolves around calculating the time required to fill a bathtub given its volume and the flow rate of water from a tap. Participants explore the relationship between flow rate, pipe dimensions, and the time to fill the bathtub, touching on both straightforward calculations and more complex considerations involving temperature effects.

Discussion Character

  • Exploratory, Technical explanation, Mathematical reasoning

Main Points Raised

  • One participant asks how to calculate the time to fill a bathtub with a known volume and water flow rate.
  • Another participant suggests that knowing the volume of water per second is essential and indicates that pressure is not necessary if velocity is known, but points out that different volumes can exist at the same velocity/pressure.
  • A participant proposes using the radius of the pipe to determine the area of the outlet, suggesting that multiplying the flow rate by the area will yield the volume of water coming out.
  • Another participant confirms that the resulting unit will be cubic meters per second and provides a formula for calculating the time to fill the bathtub, while also mentioning that temperature differences may complicate the calculation, introducing the need for a differential equation.

Areas of Agreement / Disagreement

Participants generally agree on the basic approach to calculating the time to fill the bathtub, but there are differing views on the necessity of considering temperature effects and the implications of varying pressure and velocity.

Contextual Notes

The discussion does not resolve the complexities introduced by temperature differences and their impact on the filling process, nor does it clarify the assumptions regarding the relationship between pressure, velocity, and flow rate.

Who May Find This Useful

This discussion may be useful for individuals interested in fluid dynamics, practical applications of physics in everyday scenarios, or those seeking to understand the relationship between flow rates and volume calculations.

Angello90
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Ok another stupid/smart question,

I got a bath with x m^3 volume. And a water flow rate of a tap is y m/s. I also know pressure and velocity. How can I calculate time to fill up bathtub? I know it's simple but I can not figure it out!
 
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You need to know the volume of water coming in per second, then it is easy. If you know the velocity you don't need to know the pressure. However that is not enough, you can have any volume of water at the same velocity/pressure.
 
Ok, so let's say the radius of pipe is r. This would give the area of outlet. Multiplying Q by A would give me (m/s) by (m^2), thus giving me volume of water coming out.

Does it make any sense?
 
Exactly, so you have m^3/s. If the bathtub fills up at x cubic meters then it takes x/Av seconds.

Now if it is hot or cold water then you have to account for the room temperature difference and it becomes a differential equation with an exponential coefficient in the solution.
 
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