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