notes of class 8th science chapter 8

Here’s a comprehensive set of notes for Chapter 8, "Force and Pressure," typically covered in Class 8 science.

Definition: A force is a push or pull that can change the state of motion of an object. It can also change the shape or size of an object.
Types of Forces:
- Contact Forces: Forces that act when objects are in physical contact. Examples: Friction, tension, normal force.
- Non-contact Forces: Forces that act at a distance without physical contact. Examples: Gravitational force, magnetic force, electrostatic force.

Change in Motion: Force can make an object start moving, stop moving, or change direction. For example, kicking a ball changes its motion.
Change in Shape: Force can alter the shape of an object. For example, squeezing a sponge changes its shape.
Change in Size: Force can also change the size of an object, like stretching a rubber band.

Frictional Force: A force that opposes the relative motion of two surfaces in contact.
- Static Friction: Acts when objects are not moving relative to each other.
- Kinetic Friction: Acts when objects are sliding past each other.
- Factors Affecting Friction: Roughness of surfaces, normal force, and type of materials.
Gravitational Force: The force of attraction between two masses. It pulls objects toward the center of the Earth.
- Formula: $F = mg$ where $m$ is mass and $g$ is the acceleration due to gravity (approximately $9.8 \, \text{m/s}^2$ on Earth).
Magnetic Force: The force exerted by magnets on other magnets or magnetic materials.
Electrostatic Force: The force between charged objects. Like charges repel, and opposite charges attract.

Definition: Pressure is the force applied per unit area. It describes how force is distributed over a surface.
Formula: $P = \frac{F}{A}$ where $P$ is pressure, $F$ is force, and $A$ is area.
Units of Pressure: The SI unit is Pascal (Pa). Other units include Newton per square meter (N/m²) and atmosphere (atm).

Atmospheric Pressure: The pressure exerted by the weight of the atmosphere. It decreases with altitude.
Hydrostatic Pressure: The pressure exerted by a fluid at rest. Increases with depth in a fluid.
Gauge Pressure: The pressure relative to atmospheric pressure. Measured using a pressure gauge.

In Liquids:
- Pressure in Fluids: Pressure increases with depth. Formula: $P = \rho gh$ where $\rho$ is the density of the fluid, $g$ is the acceleration due to gravity, and $h$ is the height or depth.
- Hydraulic Systems: Utilize fluid pressure to transmit force. Example: Car brakes, hydraulic lifts.
In Gases:
- Pressure and Volume Relationship: Described by Boyle's Law (for a given amount of gas at constant temperature, $P \propto \frac{1}{V}$ ).
- Pressure and Temperature Relationship: Described by Gay-Lussac's Law (for a given amount of gas at constant volume, $P \propto T$ ).
Everyday Applications:
- Pressure in Tires: High pressure in tires helps in better grip and handling.
- Cooking: Pressure cookers use high pressure to cook food faster.

Definition: The upward force exerted by a fluid on an immersed object.
Archimedes' Principle: An object immersed in a fluid experiences a buoyant force equal to the weight of the fluid displaced by the object.
Applications: Ships float because they displace a large volume of water, creating a buoyant force that supports their weight.

Balloon Experiment: When you squeeze a balloon, the pressure inside increases and the balloon expands.
Book on Table: The weight of the book exerts a downward force. The table exerts an equal and opposite upward force (normal force) that balances the weight of the book.

Force: A push or pull that changes motion or shape.
Pressure: Force per unit area; affects how we interact with liquids, gases, and solids.
Types of Forces: Frictional, gravitational, magnetic, electrostatic.
Applications: Understanding pressure helps in various fields like engineering, meteorology, and everyday life.

8th class notes (all subjects)