Class 8 chapter 15:Natural phenomena

 Some Natural Phenomena

### Introduction

Natural phenomena are events that occur in nature, often governed by physical laws.

Understanding natural phenomena can help us appreciate the complexity and beauty of the natural world.

### Lightning

1. Formation: Lightning is a massive electrostatic discharge that occurs during thunderstorms.

2. Safety precautions: During lightning storms, it's essential to take safety precautions like avoiding tall objects and staying indoors.

### Earthquakes

1. Causes: Earthquakes are caused by the movement of tectonic plates in the Earth's crust.

2. Effects: Earthquakes can cause destruction, tsunamis, and loss of life.

3. Precautions: During earthquakes, it's essential to take precautions like dropping to the ground and taking cover.

### Conclusion

Natural phenomena like lightning and earthquakes can be fascinating and awe-inspiring, but they also pose significant risks. Understanding these phenomena can help us appreciate the natural world and take necessary precautions.

Chemical effect of electric current.

 

Introduction

Electric current can cause chemical changes in certain substances.

These chemical changes can be used for various applications.

Electrolysis

1. Definition: Electrolysis is the process

of using electric current to cause a chemical change in a substance.

2. Examples: Electrolysis of water, electroplating, and extraction of metals.

Electroplating

1. Definition: Electroplating is the process of depositing a thin layer of a material on an object using electrolysis.

2. Applications: Electroplating is used to protect metals from corrosion, improve appearance, and enhance durability. 

Chemical Effects of Electric Current

1. Decomposition: Electric current can cause decomposition of certain substances.

2. Chemical reactions: Electric current can initiate chemical reactions, leading to the formation of new substances.

Applications

1. Electroplating: Used for decorative and protective purposes.

2. Purification of metals: Used to purify metals like copper and zinc.

3. Extraction of metals: Used to extract metals like aluminum and sodium.

Conclusion

Electric current can cause significant chemical changes in substances, and understanding these effects is crucial for various applications. 

Force and pressure (NCERT class 8)

 Introduction

Force is a push or pull that can change an object's state of motion or shape. It's a fundamental concept in physics that helps us understand how objects interact with each other.

Types of Forces:

There are two types of force 

1) contact force 

2)Non contact force 

A) contact force has two types 

a) Muscular force

b) Frictional force 

B) Non contact force has  types 

a) Magnetic force

b) Electrostatic force 

C) Gravitational force 

• Muscular Force: The force exerted by

our muscles, like when we lift or move objects.

• Frictional Force: The force that opposes

motion between two surfaces in contact, like when we try to slide a box on the floor.

• Magnetic Force: The force exerted by

magnets, which can attract or repel other magnets or magnetic materials.

• Electrostatic Force: The force exerted

by charged particles, like when we rub a balloon against our hair and it sticks to the wall.

• Gravitational Force: The force that pulls

objects towards each other, like the Earth's gravity pulling us towards its center.

Pressure

Pressure is the force acting per unit area on an object's surface. It's calculated by dividing the force by the area on which it acts. Pressure can be exerted by solids, liquids, and gases.

• Liquid Pressure: Liquids exert pressure

on the walls of their container and increase with depth.

•

Atmospheric Pressure: The pressure

exerted by the air around us, which is essential for our survival.

Key Concepts

• Force: A push or pull that can change an object's motion or shape.

• Pressure: The force acting per unit area on an object's surface.

•

Friction: The force opposing motion between two surfaces in contact.

•

Gravity: The force pulling objects towards each other.

Important Formulas

• Pressure = Force / Area: The formula to

calculate pressure.

• Force = Mass x Acceleration: The formula to calculate force