Name: fluid pressure in everyday life
Uploaded: 2023-04-30T11:04:12.000Z
Duration: 1 min 14 s
Channel: JoVE

K12 Standards

Alabama Course of Study Science

9-12

Physics

motion-and-stability-forces-and-interactions

Motion and Stability: Forces and Interactions

9-12.P.1.4

Pressure of Fluids

Ever wondered how a fluid flows from one point to another?
To understand this, consider a fluid of constant density at rest. If a force is applied parallel to the surface of the fluid, then to accommodate this force, the fluid is set into motion.
In contrast, if a normal force is applied on the fluid&#39;s surface, an equal and opposite force develops in the fluid as a reaction. This normal force exerted by the fluid per unit area is called pressure. The SI unit of pressure is pascal.
Pressure is always normal to any surface in contact with the fluid and so is a scalar quantity. In comparison, force has a specific direction and is a vector quantity.
The pressure at a depth h from the fluid&#39;s surface is the sum of atmospheric pressure and pressure due to the fluid&#39;s weight.
When we substitute the equivalent expressions for weight, mass, and volume, we get the pressure due to the fluid&#39;s weight as the product of density, acceleration due to gravity, and h.

pressure of fluids

There are many examples of pressure in fluids in everyday life, such as in relation to blood (high or low blood pressure) and in relation to weather (high- and low-pressure weather systems). A given force can have a significantly different effect, depending on the area over which the force is exerted. For instance, a force applied to an area of 1 mm2 has a pressure that is 100 times greater than the same force applied to an area of 1 cm2. That&#39;s why a sharp needle is able to poke through skin when a small force is exerted, but applying the same force with a finger does not puncture the skin.
Pressure is very important when discussing fluids. An important characteristic of fluids is that there is no significant resistance to the component of the force applied parallel to the surface of the fluid. The molecules of the fluid simply flow to accommodate the horizontal force. A force applied perpendicular to the surface compresses or expands the fluid. For instance, if one tries to compress a fluid, a reaction force develops at each point inside the fluid in the outward direction, balancing the force applied on the molecules at the boundary. The pressure at any point in a static fluid depends only on the depth at that point.
Pressure in a fluid near Earth varies with depth due to the weight of the fluid above a particular level. Hence, in a swimming pool, the density is approximately constant, and the water at the bottom is compressed very little by the weight of the water on top. On the other hand, traveling up in the atmosphere is quite a different situation, as the density of the air begins to change significantly just a short distance above the Earth&#39;s surface. Furthermore, fluid pressure, being a scalar quantity, has no direction, whereas the forces due to pressure have well-defined directions&#8212;they are always exerted perpendicular to any surface. The reason for this is that fluids cannot withstand or exert shearing forces. Thus, in a static fluid enclosed in a tank, the force exerted on the walls of the tank is exerted perpendicular to the inner surface. Likewise, pressure is exerted perpendicular to the surfaces of any object within the fluid.
This text is adapted from<a href="https://openstax.org/books/university-physics-volume-1/pages/14-1-fluids-density-and-pressure"> Openstax, University Physics Volume 1, Section 14.1: Fluids, Density, and Pressure.</a>

There are many examples of pressure in fluids in everyday life, such as in relation to blood (high or low blood pressure) and in relation to weather ...

Education

JoVE Core

Unit 1

Fluid Mechanics

KEY TERMS AND CONCEPTS

fluid pressure in everyday life

Fluid pressure appears in many everyday situations, including blood pressure and weather systems. The same force can have a very different effect depending on the area it acts on. A force spread over 1 mm² creates 100 times more pressure than the same force spread over 1 cm². That is why a sharp needle can pierce skin with a small force, while the same force from a finger usually does not.

Pressure is especially important when studying fluids. A fluid does not offer much resistance to a force applied parallel to its surface. Instead, the fluid molecules flow to fit that horizontal force. A force applied perpendicular to the surface behaves differently. It can compress or expand the fluid.

When a fluid is compressed, a reaction force forms inside the fluid at each point. This force acts outward and balances the force applied at the boundary. In a static fluid, the pressure at a point depends only on depth. Near Earth, fluid pressure changes with depth because of the weight of the fluid above that point.

This effect is easy to see in a swimming pool, where the water density is nearly constant. The water at the bottom is compressed very little by the water above it. The atmosphere is different because air density changes noticeably just a short distance above Earth’s surface. Pressure is a scalar quantity, so it has no direction. The forces caused by pressure do have direction, and they act perpendicular to any surface. Fluids cannot withstand or exert shearing forces, so pressure on tank walls or on objects in a fluid is always perpendicular to the surface.

Fluid Pressure in Everyday Life

characteristics of fluids

Fluid Behavior Under Force

Fluid behavior under force differs from the behavior of solids. When a force acts parallel to the top surface of a solid, the solid resists it because of internal friction between its layers. This is called shearing resistance. If the force is removed, the shearing forces help the solid return to its original shape. Other deformation forces can also change the shape of a solid for a short time, as long as the force stays below a threshold magnitude. Solids usually keep their shape, which makes...

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density

Density, Floating, and Specific Gravity

Density helps explain why objects sink or float in a fluid. It is also useful for identifying a substance and for learning about its phase and substructure. The SI unit of density is kg/m3, and the cgs unit is g/cm3. Liquids and solids usually have densities that are roughly comparable. That matches the fact that their atoms are in close contact. Gases have much lower densities than liquids and solids because their atoms are separated by large amounts of empty space. Density does not always...

Fluid pressure appears in many everyday situations, including blood pressure and weather systems. The same force can have a very different effect depending on the area it acts on. A force spread over 1 mm² creates 100 times more pressure than the same force spread over 1 cm². That is why a sharp needle can pierce skin with a small force, while the same force from a finger usually does not. Pressure is especially important when studying fluids. A fluid does not offer much resistance to a force...

variation of atmospheric pressure

Atmospheric Pressure and Altitude

Atmospheric pressure and altitude are closely linked. As height increases, atmospheric pressure decreases. This happens because the gravitational force per unit area becomes smaller as we move away from Earth’s surface. To describe this change, the atmosphere is treated with a constant air temperature at a given altitude. The ideal gas law of thermodynamics is also used as a good approximation for the air. Let p(y) be the atmospheric pressure at height y. The density ρ at y, the temperature T...

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pascal's law

Pascal’s Principle in Static Fluids

Pascal’s principle explains how pressure changes move through a fluid that is not flowing. A fluid at rest is in static equilibrium. If the fluid is water, it is in hydrostatic equilibrium. In this state, the net force on any part of the fluid must be zero, or the fluid will begin to flow. Blaise Pascal described this idea in 1653 in Treatise on the Equilibrium of Liquids. He showed that when pressure changes in an enclosed fluid, that change is transmitted without loss through the fluid and...

application of pascal's law

Hydraulic Force Transfer with Pascal's Law

Hydraulic force transfer uses Pascal's law to move pressure through an enclosed fluid. Pascal showed experimentally that a change in pressure applied to a confined fluid is transmitted undiminished throughout the fluid and to the walls of its container. That idea is the basis of hydraulics, a major part of modern mechanical technology. Hydraulic systems appear in automotive brakes, hydraulic jacks, and many other machines. A simple hydraulic system uses two pistons at the same height. Because...

pressure gauges

Gauge vs Absolute Pressure

Pressure gauges often show pressure relative to atmospheric pressure. Many gauges, including those on scuba tanks, are set to read zero at atmospheric pressure. That reading is called gauge pressure. When the pressure inside the tank is higher than atmospheric pressure, the gauge shows a positive value. Some gauges can also measure negative pressure. This is useful in a vacuum chamber, which is a rigid chamber where some air has been pumped out. Because the pressure inside the chamber is below...

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archimedes' principle

Buoyant Force from Fluid Pressure

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density and archimedes' principle

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Fluid Pressure in an Accelerating Elevator

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excess pressure inside a drop and a bubble

excess-pressure-inside-a-drop-and-a-bubble

Surface Tension in Drops and Bubbles

Surface tension sets the pressure difference in small drops and bubbles. For a tiny liquid drop, gravity can be neglected, so the drop is treated as spherical. It can also be viewed as two equal hemispherical drops joined together by surface tension. The forces on the drop come from three sources. The liquid inside pushes outward, the air outside pushes inward, and surface tension acts along the diameter between the two hemispheres. Since surface tension is force per unit length, it creates a...

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buoyancy

Buoyant Force in Sinking and Floating

Buoyant force explains why objects float, sink, or stay suspended in a fluid. A fluid can be a liquid or a gas, and every object placed in it experiences this upward force. A metal ball sinks, while a rubber ball floats. A submarine also changes its buoyancy to move up or down. The force comes from pressure changes in the fluid. Fluid pressure increases with depth because the weight of the fluid above also increases. That means the bottom of an object feels more pressure than the top. This...

contact angle

Wetting and Surface Curvature

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rise of liquid in a capillary tube

Capillary Action in Thin Tubes

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Fluid Motion Patterns in Air and Water

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bernoulli's equation

Fluid Pressure and Speed in Motion

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bernoulli's principle

Fluid Pressure and Speed Changes

Bernoulli's equation links fluid pressure and fluid speed in a static, incompressible fluid. For horizontal flow, where gravitational energy density stays constant, the equation is especially useful. In that setting, the result is known as Bernoulli's principle. Bernoulli's principle says that fluid pressure drops when speed increases, and pressure rises when speed decreases. This pressure-speed relationship helps explain how moving fluids behave in simple flow situations. It also provides a...

bernoulli's principle: applications

Bernoulli's Principle in Fluid Devices

Bernoulli's principle helps explain how many fluid devices work when the fluid moves at a constant height. It is useful for devices that use fast flow to create low pressure and for devices that measure fluid speed. Some devices use this pressure change to pull one fluid into another. These are called entrainment devices. A Bunsen burner uses an adjustable gas nozzle to entrain air for proper combustion. An atomizer uses a squeeze bulb to make a jet of air that pulls perfume drops into the...

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energy conservation and bernoulli's equation

energy-conservation-and-bernoulli-s-equation

Bernoulli’s Equation in Streamlined Flow

Bernoulli’s equation describes energy in a moving fluid. It comes from the conservation of energy principle, or the work-energy theorem, applied to an incompressible, inviscid fluid in laminar, steady, irrotational flow. The equation says that pressure energy, potential energy, and kinetic energy per unit volume stay constant along a streamline. Each term has the units of energy per unit volume. The kinetic energy per unit volume is called kinetic energy density, and the potential energy per...

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viscosity

Viscosity and How Fluids Flow

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poiseuille's law and reynolds number

Fluid Resistance, Viscosity, and Flow Regime

Fluid resistance, viscosity, and flow regime shape how liquid moves through a horizontal tube. Fluid flows from high pressure to low pressure. The flow rate, Q, is the ratio of the pressure difference to the resistance in the tube. A larger pressure difference gives a higher flow rate. Poiseuille's law describes laminar flow of an incompressible fluid in a tube. In this relation, the factors that affect flow rate except pressure are grouped into resistance. Resistance depends on the tube size...

stokes' law

Terminal Velocity in a Viscous Fluid

Viscous forces act like friction in a liquid. They resist the relative motion of molecules and pull back on a solid body moving through the fluid. The size of this force depends on the body’s shape and size, its speed, and the liquid’s viscosity, density, and temperature. For a spherical solid object, the force in a fluid is described by Stokes’ law. This law applies only at low Reynolds number, when the flow is laminar and not turbulent. Experiments show that the force is proportional to the...

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key terms and concepts

Explore fluid pressure in blood, weather, and everyday forces. Learn how depth, area, and direction affect pressure in liquids and gases.

Fluid Pressure in Everyday Life | JoVE K12

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Fluid Pressure in Everyday Life

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