8.2. Gauge Pressure and Vacuum Pressure

Now the point is what we are going to discuss is that gauge pressure and vacuum pressure. Components now is coming it what is your datum to measure the pressure. Whether you have to make a absolute zero pressure, that means you have a vacuum. From there you are measuring the pressure, or you consider as local atmosphere, to measure the pressure.

In this chunk, we are discussing the two methods of measuring pressure: gauge pressure and vacuum pressure. Gauge pressure refers to the pressure measured relative to the atmospheric pressure, while vacuum pressure measures pressure relative to a perfect vacuum, which is theoretically zero pressure. The choice of measurement reference (datum) affects how we interpret these pressures.

Think of a balloon. When you inflate it, the pressure inside it is higher than the surrounding atmospheric pressure. This excess pressure above atmospheric pressure is what we call gauge pressure. In contrast, if you measured how much pressure is inside a completely empty balloon (a vacuum), that would represent vacuum pressure, as it has no air molecules inside.

There is two conditions from where you have to measure the pressure. It could be absolute vacuum point where the pressure is equal to zero okay, theoretically it is a zero pressure. You have a vacuum where the zero pressure and you are measuring it okay. That what will come an absolute pressure.

This chunk elaborates on the two types of pressure definitions: absolute pressure and gauge pressure. Absolute pressure is the total pressure measured from a vacuum baseline (where pressure equals zero), while gauge pressure is the pressure relative to the atmospheric pressure. This is important in fluid mechanics, as many pressure calculations are based on gauge pressure, which reflects how much pressure is exerted above what the atmosphere is exerting.

Think of diving underwater. As you dive deeper, the water pressure increases. If you have a pressure gauge that reads how much pressure you're experiencing above the pressure at the surface (atmospheric pressure), that is your gauge pressure. Absolute pressure would consider the weight of the water above you, starting from the vacuum of space as the zero point.

But if you most of the case as you know it when you consider the fluid all the fluid will have a surrounding of a part of atmosphere. Most of the cases what we consider here, we are not solving the problems in a space or area. We are just solving or any other planets, we are just solving the very simplified problems in and around the earth. So we consider the atmospheric pressure is the datum to measure the pressure.

In many practical applications, pressure is often measured relative to atmospheric pressure. The atmospheric pressure serves as a baseline reference (datum). To find absolute pressure from gauge pressure, you need to add atmospheric pressure to the gauge pressure. This is an essential step to ensure that calculations reflect the true pressure exerted by a fluid.

Imagine you're baking a cake at sea level where atmospheric pressure is constant. If your recipe calls for measuring the pressure of a gas at certain points, you would always add the pressure above atmospheric, which is like considering how high your cake rises compared to the outside environment.

So we can have a pressure measurement either from the vacuum or from the atmospheric pressure. If you need to compute it what will be the absolute pressure, then it is a very easy. You just use whether the gauge pressure or this the vacuum pressure that difference what we can get it that what you just add with atmospheric pressure to get the absolute pressure.

This chunk presents the formulas to derive both gauge and vacuum pressures. If the gauge pressure is known, it can be expressed as the difference between the absolute pressure and atmospheric pressure. Similarly, vacuum pressure is considered when the measurement density is below atmospheric pressure, and it is negatively referenced to atmospheric pressure.

Consider a high-pressure gas cylinder. The gauge pressure shows how much pressure is inside compared to the outside air. If it shows 200 kPa, and the atmospheric pressure is 100 kPa, then the absolute pressure inside the cylinder is 200 kPa (gauge) + 100 kPa (atmospheric) = 300 kPa (absolute).

We talked about the pressure distributions as it indicates is that the pressure is equal all over that surface. That is the conditions we consider to solve many fluid flow problems in hydrostatic and second thing is that you can easily know it if I consider a and one point, definitely the pressure at the one so do we call more than pressure at the air because if you consider the virtual fluid balls also the weight of the water and weight of the waters here that what is different.

This chunk discusses how pressure in a fluid at rest is equal across any horizontal surface. This property is fundamental in hydrostatics. If you compare pressures at different depths in a fluid, you'll notice that the deeper you go, the greater the pressure due to the weight of the fluid above. This is also simple to visualize when considering how higher density brews or liquid mixtures can exert different pressures at the same depths.

Imagine an underwater scuba diver. As they descend into the water, the pressure they feel increases because of the weight of the water above them. If they were at five meters, they would experience more pressure than at one meter, mimicking how different fluid depths impact pressure readings.

Now let me consider the capillary effect as you could have seen some of the books if any of the class 12th levels. What do we do it we just coming the two force components, the force due to the surface tensions and the gravity force of the capillary part.

In this chunk, the concept of capillary action is introduced. Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of external forces. This phenomenon is largely due to surface tension and adhesive forces between the liquid and surrounding material. The balance of forces between gravity pulling down and surface tension pulling up results in a characteristic height rise in a liquid within a narrow tube.

A good example of capillary action that many people can relate to is how a paper towel absorbs spilled liquid. The towel’s fibers create tiny spaces that allow the liquid to rise through it, demonstrating surface tension and how liquids behave in narrow spaces.

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