# What is Dynamic Pressure? - Definition & Equation

Instructor: David Redmond

David has been an mechanical engineering manager, designing products for 20 years. He has a Bachelor's Degree in Mechanical Engineer and is trained in Design for Six Sigma

In this lesson, you will learn the difference between static and dynamic pressure. In addition, you will learn how to calculate each type of pressure and how each is applied in real world applications.

## Under Pressure

If you want to bounce a basketball, you must inflate the ball with air. Have you ever noticed that as the outside surface of the ball becomes harder, it is more difficult to pump more air inside the ball? What you are experiencing is pressure. Pressure is the amount of force divided by the area over which the force is being applied. In the case of a basketball, the area would be the inside surface of the ball. The pressure inside of a basketball is called static pressure. Static pressure is exactly as it sounds. It is a measurement of pressure when the fluid (in the case of a basketball, the fluid is the air) is standing still or is static. Static pressure is uniform in all direction and can be expressed in the following formula:

Static Pressure is the most common type of pressure that you experience in everyday life. Now that we know what static pressure is, let's talk about dynamic pressure.

## Moving Pressure

If you fill a pipe with water and close both ends, the water also exerts static pressure on the pipe and end caps. However, what happens when you open the ends of the pipe, and the water starts moving? When a fluid is moving through a pipe, there is a second component to the pressure. It is called dynamic pressure. Dynamic pressure is a pressure exerted perpendicular to the direction of the flow and is represented by the symbol q. The equation for dynamic pressure is as follows:

This equation is only applicable for incompressible fluids like water or oil. Incompressible means that fluid density remains constant. If we go back to the basketball example, the air inside the basketball is compressed and the density changes as the pressure increases. Thus, air is not incompressible. Dynamic pressure can also be referred to as velocity pressure as it is a result of the velocity of the fluid inside the pipe.

## Dynamic Pressure in Action

Let's look at an example. I am going to use metric or SI units in this example. However, the same equation can be used with imperial units of measure as well.

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