Explanation of experiments and questions of ncert class 8 chapter 11 Force and pressure.

 Force

Questions 1-2: Push and Pull

1. Give two examples each of situations where you push or pull to change the state of motion of objects.

Push: Closing a drawer, moving a wooden box.

Pull: Drawing water from a well, a horse pulling a cart.

2. Give two examples where applied force causes a change in shape.

Applying force on a rubber band to stretch it.

Applying force on clay to change its shape.

Forces and Their Types

Question 3: Fill in the Blanks

To draw water from a well, we have to pull at the rope.

A charged body attracts an uncharged body towards it.

To move a loaded trolley, we have to push it.

The north pole of a magnet repels the north pole of another magnet.Force and Motion

Question 4: Archer Stretching Bow

To stretch the bow, the archer applies a force that causes a change in its shape.

The force applied by the archer is an example of muscular force.

The type of force responsible for the change in motion of the arrow is a contact force.

Forces acting on the arrow are due to gravity and friction of air.

Experiments

Experiment 1: Ball on a Level Surface

When a ball is pushed gently on a level surface, it begins to move.

When pushed again while moving, its speed increases.

When palm is placed in front of the moving ball, its speed decreases.

Experiment 2: Ball and Ruler

When a ruler is placed in the path of a moving ball, the ball changes direction after striking the ruler.

This shows that force can chang

Experiment 3: Magnetism

When unlike poles of two magnets are brought near each other, they attract.

When like poles are brought near each other, they repel.

This shows that magnetic force is a type of non-contact force.

Experiment 4:

Electrostatic Force

When a straw is rubbed with paper, it attracts another straw.

If both straws are rubbed with paper, they repel each other.

This shows that electrostatic force can act between charged bodies.

Pressure

Experiment 5:

Pressure Exerted by Liquids

When water is poured into a bottle with holes at the same height, water streams out at the same distance.

This shows that liquids exert equal p

Experiment 6: Atmospheric Pressure

When a rubber sucker is pressed on a smooth surface, it sticks due to atmospheric pressure.

To pull the sucker off, a large force is required to overcome atmospheric pressure 1.ressure at the same depth.e the direction of motion.

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

Chapter 6: Acid and Base : what's the differences

 Understanding Acids and Bases

Have you ever wondered why certain substances taste sour or bitter? The reason behind these distinct tastes lies in the nature of the substance itself. In this chapter, we will delve into the world of acids and bases to understand their properties, characteristics, and uses.

What are Acids?

In simple terms, acids are substances that donate hydrogen ions (H+) or have a pH value less than 7.

Characteristics of Acids:

1. Sour taste

2. Corrosive nature

3. React with metals to release hydrogen gas (H2)

4. Turn litmus paper red and phenolphthalein colorless

Examples of Acids:

• Citrus fruits (oranges, lemons, limes)

• Vinegar (acetic acid)

• Tomatoes (citric acid)

• Stomach acid (hydrochloric acid)

• Soda (phosphoric acid or citric acid)

Uses of Acids:

• Cleaning agents

• Food preservatives

• Pharmaceuticals

What are Bases?

Bases are substances that accept hydrogen ions (H+) or have a pH value greater than 7.

Characteristics of Bases:

1. Bitter taste

2. Soapy feel

3. React with oils, fats, and greases

4. Turn litmus paper blue and phenolphthalein pink

Examples of Bases:

• Soap

• Sodium hydroxide (NaOH)

• Baking soda (sodium bicarbonate)

• Bleach (sodium hypochlorite)

• Toothpaste (sodium fluoride)

• Ammonia (ammonium hydroxide)

Uses of Bases:

• Cleaning agents

• Detergents

• Disinfectants

• Personal care products (skin pH balance, oral health, hair care)

• Medicine (anti-ulcer drugs, antibiotics)

• Industry (paper, textile, water treatment)

Neutralization Reaction

When an acid and a base react, they form a salt and water. This reaction is called neutralization.

Example of Neutralization Reaction:

HCI (hydrochloric acid) + NaOH (sodium hydroxide) → NaCl (sodium chloride) + H2O (water)

Conclusion

In conclusion, acids and bases are two classes of substances that play important roles in our daily lives. Understanding their properties, characteristics, and uses can help us appreciate the world around us.

Chemical reaction 101 :a biginners guide

 Chemical reactions are the building blocks of chemistry, and understanding them is essential for any aspiring chemist or science enthusiast. In this guide, we'll cover the basics of chemical reactions, including what they are, how they work, and some common types.

What is a Chemical Reaction?

A chemical reaction is a process where one or more substances (reactants) are converted into new substances (products). This process involves the breaking and forming of chemical bonds between atoms.

Key Components of a Chemical Reaction

1. Reactants: The substances that undergo a chemical change.

2. Products: The new substances formed as a result of the reaction.

3. Catalyst: A substance that speeds up the reaction without being consumed.

4. Energy: Often required to initiate or sustain the reaction.

Types of Chemical Reactions:

1. Synthesis Reaction: Two or more reactants combine to form a new product.

Example: 2H2 + O2 → 2H2O

2. Decomposition Reaction: A single reactant breaks down into two or more products.

Example: 2H2O → 2H2 + O2

3. Replacement Reaction: One reactant replaces another reactant in a compound.

Example: Zn + CuSO4 → ZnSO4 + Cu

4. Combustion Reaction: A reactant combines with oxygen to produce heat and light.

Example: CH4 + 202 → CO2 + 2H2O

Chemical Reaction Equations:

Chemical reaction equations are used to represent the reactants, products, and catalysts involved in a reaction. The equation is balanced to ensure that the number of atoms for each element is the same on both the reactant and product sides.

Tips for Balancing Chemical Equations:

1. Count the atoms: Ensure that the

number of atoms for each element is the same on both sides.

2. Use coefficients: Add numbers in front of the formulas of the reactants or products to balance the equation.

3. Check your work: Verify that the equation is balanced by re-counting the atoms.

Common Chemical Reaction Symbols:

→ (arrow): indicates the direction of the reaction

= (double arrow): indicates a reversible reaction

• ▲ (delta): indicates heat is added to the reaction

• catalyst: a substance that speeds up the reaction without being consumed

Chemistry with a twist : Chapter 1

 The Fun World of Helium: Exploring its Properties and Uses

Manisha:

 I welcome you all in

 Chemistry with a twist here we make chemistry fun and easy to understand. Today, we're excited to have Mr. Helium as our guest. Let's get to know him better.

Helium: 

Hello, Manisha! Thanks for having me. I'm Helium, a chemical element with the symbol He and atomic number 2.

Manisha:

 That's fascinating, Helium. Can you tell us a bit about yourself?

Helium: 

I'm a noble gas, which means I'm unreactive and stable. I'm also the second-lightest element in the universe.

Manisha: 

Wow, that's amazing. Helium is used in various applications, including party balloons and airships. But why is it used in these applications?

Helium:

It's because I'm extremely light, with a density about 1/7th that of air. Plus, I'm an inert gas, which means I don't react with other elements.

Manisha: 

That makes sense. Helium is

also used in medical applications, such as cooling superconducting magnets in MRI machines. Can you tell us more about that?

Helium: 

Ah, yes! My extremely low boiling point (-268.93°C) makes me an ideal coolant for these applications.

Manisha: 

That's really cool. Thanks for sharing your story with us, Helium.

Helium:

 Thanks for having me, Manisha. It was a blast!

Manisha: 

Don't forget to subscribe to our page for more fun chemistry content. Thanks for reading and we'll see you in the next chapter !

Chemistry for beginners chapter 5:The periodic table

 In this article we are going to know about periodic table, it's structure and most importantly, how to use it, so, let's begin the journey :

What is periodic table:

"There are a lot of elements in nature, and it's very difficult to remember them and their properties individually. So, scientists decided to arrange them in a manner, and here comes our hero - the periodic table! The mighty periodic table is a tabular arrangement of elements, organized according to their chemical properties."

The Structure of the Periodic Table:

The structure of the periodic table is very simple, consisting of only three things: rows, columns, and blocks.

• Rows: Called periods, which are arranged horizontally.

• Columns: Called groups or families, which are arranged vertically.

• Blocks: Larger sections of the table determined by the electronic configuration of the elements.

Here are some basic tips:

1. Find an Element: Look at the symbol of the element (e.g., H for hydrogen) or its atomic number (e.g., 1 for hydrogen).

2. Identify the Group: Elements in the same group (vertical column) have similar chemical properties.

3. Identify the Period: Elements in the same period (horizontal row) show a gradual change in properties.

4. Determine the Block: There are four blocks in the periodic table (s, p, d, and f). Elements in the same block have similar electronic configurations.

5. Predict Properties: Use the periodic table to predict an element's properties, such as its reactivity, electronic configuration, or ionization energy.

Tips and Tricks:

1. Memorize at least 20 elements for a basic understanding.

2. Use flashcards to associate elements with their symbols and properties.

3. Practice as much as you can.

Why Hydrogen bond is stronger than covalent bond.

 Did you know that there is a type of chemical bond that can be stronger than a covalent bond, yet it's not a covalent bond itself?

This phenomenon is known as the "Hydrogen Bond".

What is a Hydrogen Bond?

A hydrogen bond is a type of intermolecular force that arises between molecules with a hydrogen atom bonded to a highly electronegative atom, such as oxygen, nitrogen, or fluorine. This bond is not a covalent bond, but rather a weak electrostatic attraction between the partially positive hydrogen atom and the partially negative electronegative atom.

How Strong Can Hydrogen Bonds Be?

Hydrogen bonds can be surprisingly strong, with energies ranging from 1-30 kJ/mol. To put this into perspective, the energy of a typical covalent bond is around 100-1000 kJ/mol. While hydrogen bonds are generally weaker than covalent bonds, they can still play a crucial role in determining the structure and properties of molecules.

Real-World Examples of Hydrogen Bonding

Hydrogen bonding is responsible for many fascinating phenomena in chemistry and biology, such as:

1 . Water's High Boiling Point: Hydrogen

bonds between water molecules require a lot of energy to break, resulting in water's unusually high boiling point.

2. DNA's Double Helix Structure:

Hydrogen bonds between the base pairs of DNA (adenine-thymine and guanine-cytosine) hold the double helix structure together.

3. Protein Folding: Hydrogen bonds

play a crucial role in determining the three-dimensional structure of proteins.

In conclusion, 

hydrogen bonds are a

remarkable example of the complex and fascinating world of intermolecular forces. Their unique properties and strengths make them essential for understanding many chemical and biological phenomenon.