# Rate of flow, or velocity of fluid?

• Doug1943
In summary, the conversation discusses a classic demonstration that shows how water pressure increases with depth. The author may have meant "velocity" instead of "rate of flow" when describing the relationship between hole size and flow. However, the terminology used is ambiguous, so it is unclear if the author was correct or not.

#### Doug1943

I was looking at a site which described the classic demonstration to illustrate how water pressure increases with depth (shown by punching three holes, one above the other separated by a few centimeters, in a container of water): "The smaller the holes, the greater the rate of flow from the holes."

Is this right? Does not the author mean, "The smaller the holes, the greater the velocity of the water"? (I think of "rate of flow" as being total volume passing a point per unit time, which must remain constant. And presumably these relationships only hold when the flow is laminar and frictional forces are neglected?)

I believe you are correct, the author meant velocity. Otherwise the continuity equation would be violated.

cross sectional area x velocity = constant

It depends on what the author said. If he/she just said "flow rate" or "rate of flow", those are ambiguous terms and so they may have simply meant velocity rather than volumetric flow rate or mass flow rate. In other words, they may have been right or wrong but you can't really tell because the terminology as you describe it is ambiguous.

If the holes are equal in size, then different flow velocity necessarily means different mass/volumetric flow, for liquids.

Yes, you are correct. The author likely meant to say "the greater the velocity of the water" rather than "the greater the rate of flow." Rate of flow refers to the total volume passing a point per unit time, as you mentioned, and this would remain constant in this demonstration. The velocity of the water, on the other hand, would increase as the holes become smaller because the same amount of water is being forced through a smaller area, resulting in a higher velocity. It is important to consider factors such as laminar flow and frictional forces in this demonstration, as they can affect the accuracy of the results.

## 1. What is the difference between rate of flow and velocity of fluid?

The rate of flow refers to the volume of fluid that passes through a certain point within a specific period of time, while velocity of fluid refers to the speed at which the fluid is moving in a particular direction.

## 2. How is the rate of flow or velocity of fluid measured?

The rate of flow can be measured using a flowmeter, which measures the volume of fluid passing through in a given time. Velocity of fluid can be measured using a pitot tube or an anemometer.

## 3. What factors affect the rate of flow or velocity of fluid?

The rate of flow and velocity of fluid are affected by factors such as the viscosity of the fluid, the size and shape of the container or channel through which the fluid is flowing, and the pressure or force applied to the fluid.

## 4. How can the rate of flow or velocity of fluid be controlled?

The rate of flow or velocity of fluid can be controlled by adjusting the size of the opening or valve through which the fluid is flowing, changing the pressure or force applied to the fluid, or altering the properties of the fluid itself (such as temperature or viscosity).

## 5. What are some real-world applications of understanding rate of flow and velocity of fluid?

Understanding the rate of flow and velocity of fluid is crucial in many industries, such as manufacturing, transportation, and environmental engineering. It is used to design efficient pipelines, study the flow of blood in the human body, and predict the behavior of fluids in weather systems, among others.