What is Fluid?
Do you ever wonder why some substances flow? And why do some substances flow differently from others? Do only liquids flow? What are these substances? Answers to all of these questions will be answered today. All these phenomena are associated with fluids.
The scientific fluid definition is very simple to understand. Fluid meaning refers to a substance that does not have a definite shape and yields easily to external pressure. It can be a liquid or a gas. We say that a fluid can flow easily and we find its applications more in clutch or coupling, where fluid helps transmit the power supply.
Fluid Examples in Everyday Life
You might have heard of the word ‘Fluid’; now, we will look at some examples of everyday use of this term to understand it better.
The patient is severely dehydrated, and he needs fluids urgently.
The tanks on the rooftop are placed for storing fluids like oil, kerosene, and gas.
We generally keep our household cleaning fluids out of the reach of the children.
Our stomach collects gastric fluids around its edge to digest food.
We saw some kind of fluid oozing (a viscous liquid) coming out from the trunk of the tree.
Fluid Definition in Physics
In Physics, the fluid definition is:
A fluid is a substance that continually flows or deforms when we subject it to shear stress or external force.
The fluid is one of the phases of matter and we consider fluids like liquids, gases, and plasmas. One of the scientific definitions of fluid is that these are substances with zero shear modulus, or, in simpler words, these substances cannot resist the shear force applied to them.
Fluid Information Definition
To understand fluid information definition, let’s consider the below one-line statements:
The term ‘fluid’ is more closely related to being a solid plasma; however, we consider it as liquid and gas. A fluid carries no shear modulus. Now, let’s understand the types of fluid flow:
Fluid flow has of the following types:
Steady or unsteady
Compressible or incompressible
Viscous or non-viscous, and
Rotational or irrotational.
Steady or Unsteady Flow
The flow of fluid can either be steady or unsteady, depending on the velocity of the fluid:
Steady: In steady fluid flow, the fluid’s density remains constant at every point.
Unsteady: During the unsteady flow, the fluid’s velocity differs between any two points.
Viscous or Non-Viscous Flow
Liquid flow can be vicious or non-viscous.
The resistance offered by a fluid to flow is known as viscosity. A fluid that offers high resistance to flowing is known as a viscous fluid and its flow is said to be vicious.
On the contrary, a fluid that flows relatively freely is said to have low viscosity or is known as a non-viscous fluid and its flow is said to be non-viscous.
Viscosity is a measure of the thickness of a fluid, and very sticky fluids viz: motor oil or shampoo are called viscous fluids.
Fluid Characteristics
We see ‘fluid definition’ a lot many times; however, ‘fluid’ is used in everyday life and is understood with some of its characteristics.
Now, let’s look at some characteristics of a fluid:
Capable of flowing and easily changing its shape.
Constantly changing or apt to variations.
Smooth in movement, i.e., easy flow.
Types of Fluids
Now, let’s look at types of fluid.
The Types of Fluids are:
Ideal Fluid: An ideal fluid is incompressible and it is an imaginary fluid that doesn’t exist in reality. Also, it doesn’t have viscosity. In the real world, ideal fluid does not exist.
Ideal plastic Fluid: When the shear stress becomes proportional to the velocity gradient and more than the yield value, the fluid is said to be the ideal plastic fluid. E.g., Water suspension of clay and fly ash
Real Fluid: Fluids having viscosity are real fluids. E.g., petrol
Newtonian Fluid: A fluid obeying Newton’s law of viscosity is known as a Newtonian fluid. E.g., glycerol thin motor oil.
Non-Newtonian Fluid: A fluid not obeying Newton’s law of viscosity is said to be a Non-Newtonian fluid. E.g., cornflour and water
Incompressible Fluid: When the density of the fluid remains invariant with the application of external force, it is said to be an incompressible fluid. E.g., The stream of water flowing at high speed from a garden hose pipe
Compressible Fluid: When the density of the fluid varies with the application of external force, it is a compressible fluid. E.g., gas, steam, etc.
Interesting Facts About Fluids
A very common fact about fluids is that they have a constant volume, meaning that they are confined within the vessel they are kept in.
Now, let’s look at a few more interesting facts about fluids.
A fluid that is a liquid has the following properties.
After cooling liquids, we can compress them, except for ice, which expands.
We cannot compress water.
Water has three forms - solid, liquid, and gas(vapor)
The liquid form of fluid is a prerequisite of carbon-based life
Most of the water present on the earth is from outer space.
Cats release a lot of fluid in the saliva.
Fluid mechanics is the study of the forces on the fluid and how fluids move. Fluid mechanics can be divided into parts: fluid statics and fluid dynamics. Fluid statics is the study of fluids at rest, and fluid dynamics is the study of fluids in motion.
Fluid mechanics is a branch of continuum mechanics, a subject that models matter without using the information of what atoms they are made of.
Why study Fluid from Vedantu?
Fluid is an extremely important topic in Physics. An entire branch is dedicated to its study. Here Vedantu has tried to cover the topic for you as holistically as possible. After going through this, you will gain enough theoretical understanding of the topic to tackle questions based on basics. It will also facilitate you to understand the advanced level concepts. Going through it thoroughly will not only help you fetch marks in the upcoming exams but also in other future exams which may include this topic.
Conclusion
This section has discussed the topic of Fluid for you in brief. The aim was to cover the fundamentals of the topic. Here we have covered standard definitions, characteristics, types, examples, and fun facts about the fluid and related phenomenon. All the content made available to you is of the utmost quality. To fuel your curiosity further, Vedantu has also added a few fun facts in the last part of the topic. You should go ahead and make the best use of this content and many other materials made available to you by Vedantu.
FAQs on Fluid
1. What is a fluid in physics?
In physics, a fluid is any substance that can flow and takes the shape of its container. This includes both liquids (like water and oil) and gases (like air and oxygen). Unlike solids, fluids cannot resist shear stress and will deform continuously when a force is applied.
2. What are some common examples of fluids in daily life?
You can find fluids everywhere in daily life. Common examples include:
- Water: The most common liquid fluid we drink and use.
- Air: The mixture of gases we breathe is a fluid.
- Honey: A thick, viscous fluid that flows slowly.
- Milk: A liquid fluid we consume.
- Smoke: A collection of airborne particles and gases that behaves like a fluid.
3. What is the difference between a liquid and a gas, since both are fluids?
The main difference lies in their compressibility and volume. Liquids are nearly incompressible and have a definite volume, meaning they will fill the bottom of a container but keep their own volume. Gases, on the other hand, are highly compressible and have no definite volume; they will expand to fill the entire container they are in.
4. What is Pascal's Law and where is it applied?
Pascal's Law states that a pressure change at any point in a confined, incompressible fluid is transmitted equally to all points throughout the fluid. This principle is the basis for hydraulic systems. A common application is in a car's hydraulic brakes, where pressing the brake pedal applies a small force that gets multiplied to stop the car.
5. How does Bernoulli's principle explain how an airplane flies?
Bernoulli's principle states that for a fluid, an increase in speed results in a decrease in pressure. An airplane's wing is designed to be curved on top and flatter on the bottom. This shape forces the air to travel faster over the top surface than the bottom. The faster-moving air on top creates a region of lower pressure, while the slower air below has higher pressure. This pressure difference creates an upward force called lift, which pushes the airplane up.
6. What is the difference between streamline and turbulent flow?
The key difference is the path of the fluid particles.
- In streamline flow (or laminar flow), each particle follows a smooth, predictable path, and the paths of different particles do not cross. Think of a smoothly flowing river.
- In turbulent flow, the fluid moves in an irregular, chaotic manner with eddies and swirls. Think of a rapidly flowing, churning river or smoke rising from a fire.
7. Why do some liquids, like honey, flow slower than others, like water?
This is due to a property called viscosity, which is essentially the internal friction of a fluid. Honey has a high viscosity, meaning its internal layers resist flowing past each other, making it flow slowly. Water has a low viscosity, so its layers slide past each other easily, allowing it to flow quickly.
8. What is surface tension and why can insects walk on water?
Surface tension is the tendency of liquid surfaces to shrink into the minimum possible surface area. It's like an elastic skin on the water's surface, caused by the cohesive forces between water molecules. This 'skin' is strong enough to support the weight of small insects like water striders, allowing them to walk on water without sinking.
9. What makes a fluid 'ideal' and why do we use this concept in physics?
An ideal fluid is a theoretical concept used to simplify calculations in fluid dynamics. It has two main properties: it is non-viscous (has no internal friction) and it is incompressible (its density is constant). Real fluids do not have these properties, but the ideal fluid model helps us understand fundamental principles like Bernoulli's theorem more easily before applying them to more complex, real-world situations.
10. How does Archimedes' principle help determine if an object will float or sink?
Archimedes' principle states that any object submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces. An object will float if the buoyant force is greater than or equal to its own weight. It will sink if its weight is greater than the buoyant force. This is why a heavy steel ship can float—its shape displaces a huge volume of water, creating a large buoyant force.
