9th Class Physics Unit No.7 Properties of Matter Notes
Atmospheric Pressure
- Atmospheric pressure is the force per unit area exerted by the Earth’s atmosphere on any surface.
- It is caused by the weight of the air above the surface. Atmospheric pressure acts in all directions and is responsible for many everyday phenomena.
Action of Sucking through a Straw
When you suck through a straw, you create a partial vacuum inside the straw. Atmospheric pressure acts on the liquid in the glass, pushing it up into the straw to fill the vacuum. As a result, the liquid rises in the straw and you can drink it.
Action of Sucking through a Dropper or Syringe
Sucking through a dropper or syringe works on the same principle as using a straw. By creating a partial vacuum inside the dropper or syringe, you cause the liquid to be drawn into it from the container.
Action of a Vacuum Cleaner
A vacuum cleaner works by creating a low-pressure area (vacuum) inside its nozzle. This lower pressure causes air and dust particles to be sucked into the cleaner, cleaning the surface.
Properties of Matter
- Matter exists in three states: solid, liquid, and gas.
- Matter has weight and occupies space.
- Solids have a definite shape, while liquids and gases do not.
- Liquids have a definite volume, while gases do not have a fixed volume.
- Various materials differ in their hardness, density, solubility, flow, elasticity, conductivity, and other qualities.
Kinetic Molecular Model of Matter
- Matter is composed of particles called molecules.
- These molecules are in constant motion.
- Molecules attract each other.
- Chapter No.1 Introduction to Biology
- Chapter No. 2 Solving a Biological Problem
- Chapter No.3 Biodiversity
- Chapter No.4 Cells and Tissues
- Chapter No.5 Cell Cycle
SOLIDS
Solids are a state of matter characterized by their fixed shape and volume. The molecules in solids are held closely together by strong forces of attraction, resulting in a relatively rigid structure. While the molecules in solids do vibrate about their mean positions, they do not move from place to place, maintaining their overall shape.
Examples of solids include stones, metal spoons, pencils, and other objects with a fixed form.
LIQUIDS
Liquids, on the other hand, have molecules that are more spaced out compared to solids, resulting in weaker attractive forces between them. This allows the molecules in a liquid to slide over one another, giving liquids the ability to flow and take the shape of the container they are put in. However, like solids, molecules in liquids also vibrate around their mean positions.
Examples of liquids include water, cooking oil, and other substances that can flow and conform to the shape of their containers.
GASES
Gases have no fixed shape or volume and are characterized by having molecules that are much farther apart than in solids or liquids. Gases are lightweight and can be compressed into smaller volumes. The molecules in gases have random motion and move with high velocities. They constantly collide with the walls of the container they are in, exerting pressure on those walls.
Examples of gases include air and other substances that can be filled in any container of any shape.
PLASMA – THE FOURTH STATE OF MATTER
Plasma is considered the fourth state of matter and is formed when a gas is heated to such high temperatures that its atoms lose their electrons, becoming positive ions. This ionic state of matter is highly conducting and allows electric current to pass through it. Plasma is found in stars like our Sun and fills a significant portion of the universe.
Examples of plasma include neon and fluorescent tubes when they glow and various phenomena occurring in stars and other celestial bodies.
DENSITY
Density is a property of matter defined as its mass per unit volume. It is a measure of how much mass is contained within a given volume. The formula for density is:
Density = Mass / Volume
The SI unit of density is kilograms per cubic meter (kg/m^3). Different substances have different densities, as shown in the table provided.
PRESSURE
Pressure is defined as the force acting per unit area on the surface of an object or substance. In the context of liquids and gases, it is the force per unit area exerted by the molecules on the walls of a container or any object immersed in them. Pressure is a scalar quantity and is measured in pascals (Pa).
ATMOSPHERIC PRESSURE
Atmospheric pressure is the pressure exerted by the Earth’s atmosphere on everything within it. It decreases with increasing altitude. At sea level, the atmospheric pressure is approximately 101,300 pascals (Pa) or 101,300 newtons per square meter (Nm^2). Barometers are used to measure atmospheric pressure.
PRESSURE IN LIQUIDS
In liquids, pressure increases with depth. This is due to the weight of the liquid above a certain depth, which exerts a force on the underlying liquid layers. Pascal’s law states that any change in pressure applied to a confined liquid is transmitted equally in all directions.
APPLICATIONS OF PASCAL’S LAW
Pascal’s law finds applications in various fields, including hydraulic systems such as hydraulic presses and hydraulic brakes in vehicles. Hydraulic systems use the principle of pressure transmission to multiply forces and perform various tasks effectively.
ARCHIMEDES PRINCIPLE
Archimedes’ principle states that when an object is immersed (partially or fully) in a fluid (liquid or gas), it experiences an upthrust or buoyant force equal to the weight of the fluid displaced by the object. The principle is named after the ancient Greek mathematician and physicist Archimedes, who first described it around the 3rd century BC.
Key Points
Upthrust or buoyant force: When an object is placed in a fluid, the fluid exerts an upward force on the object. This force is called upthrust or buoyant force.
Weight of displaced fluid: The magnitude of the upthrust is equal to the weight of the fluid displaced by the object. This principle holds true for both liquids and gases.
Floating and sinking: If the weight of the object is less than the upthrust, the object will float. If the weight of the object is greater than the upthrust, the object will sink. If the weight of the object is equal to the upthrust, the object will remain suspended at a constant depth in the fluid.
Partial immersion: Archimedes’ principle also applies to objects that are partially immersed in a fluid. In this case, only the volume of the object submerged contributes to the upthrust.
Applications
Ship buoyancy: The principle of buoyancy is essential in designing ships and boats. By ensuring that the weight of the ship is less than the weight of the water it displaces, the ship can float and carry its cargo.
Hot air balloons: Hot air balloons work on the principle of buoyancy. As the air inside the balloon is heated, it becomes less dense than the surrounding air, creating an upthrust that lifts the balloon.
Submarines: Submarines use ballast tanks to control their buoyancy. By adjusting the amount of water in these tanks, the submarine can control its depth and either surface or dive.
Life jackets: Life jackets provide buoyancy to keep a person afloat in water. The life jacket displaces enough water to generate an upthrust greater than the person’s weight, helping them float.
Archimedes’ principle is a fundamental concept in fluid mechanics and plays a significant role in various practical applications, especially in the design and operation of objects that interact with fluids.
ELASTICITY
Elasticity is a property of materials that allows them to undergo deformation when subjected to external forces and return to their original shape and size after the force is removed. It is the ability of a material to resist permanent deformation and recover its original form.
STRESS
Stress is the force applied to a material per unit area on its surface. Mathematically, stress (σ) is defined as:
Stress (σ) = Force (F) / Area (A)
The SI unit of stress is newton per square meter (Nm^2) or pascal (Pa). Stress is responsible for causing deformation in a material.
STRAIN
Strain is the measure of the deformation or change in shape of a material in response to stress. It is the ratio of the change in size or shape of a material to its original size or shape. Strain is a dimensionless quantity.
Strain (ε) = Change in dimension / Original dimension
HOOKE’S LAW
Hooke’s law states that the strain produced in a material is directly proportional to the stress applied within the elastic limit of the material. In other words, as long as the applied stress remains within the elastic limit, the material will exhibit linear elasticity, and the strain will be directly proportional to the stress.
Hooke’s law can be expressed mathematically as:
Stress (σ) = Young’s Modulus (Y) × Strain (ε)
where Young’s Modulus (Y) is a constant of proportionality specific to each material and is a measure of its stiffness or resistance to deformation.
YOUNG’S MODULUS
Young’s Modulus (Y) is a material property that measures its stiffness or resistance to deformation when subjected to a force. It is the ratio of stress to strain within the elastic limit of the material.
Young’s Modulus (Y) = Stress (σ) / Strain (ε)
The SI unit of Young’s Modulus is pascal (Pa) or newton per square meter (Nm^2). It quantifies how much a material will stretch or compress in response to an applied force.