Science Class 8 - Force And-Pressure Notes

Force and Pressure

Welcome to the chapter on Force and Pressure for Class 8. In this chapter, you will learn what force and pressure are, how they work in our daily life, and how they affect objects around us. By the end of this chapter, you will understand the types of forces, how pressure is created, and how to solve problems related to force and pressure!

Introduction

Force and pressure are important concepts in physics. Force is a push or pull that can change the state of motion or shape of an object. Pressure is the force applied on a surface per unit area.

What is Force?

• A force is a push or pull acting on an object.
• Force can make an object move, stop, change direction, or change shape.
• Force is measured in newtons (N).

Examples: Kicking a football, pulling a cart, squeezing a sponge.

Types of Forces

• Contact Force: Forces that act when objects touch each other (e.g., friction, muscular force).
• Non-contact Force: Forces that act without touching (e.g., gravitational force, magnetic force, electrostatic force).

Effects of Force

• Change the speed of an object (make it move faster or slower).
• Change the direction of a moving object.
• Change the shape or size of an object.

What is Pressure?

Pressure is the force applied on a surface divided by the area of that surface.

• Pressure = Force ÷ Area
• Pressure is measured in pascals (Pa).

Example: When you press a pin on a board, the small area of the pin creates high pressure.

Pressure in Everyday Life

• Sharp knives cut better because they apply more pressure on a small area.
• Wide tires of tractors reduce pressure and prevent sinking in soft soil.
• School bags with wide straps put less pressure on your shoulders.

Pressure in Liquids and Gases

• Liquids and gases exert pressure in all directions.
• Air pressure helps us breathe and keeps weather patterns moving.
• Water pressure increases with depth in oceans and lakes.

Fun Activity: Balloon Experiment

Blow up a balloon and press it gently. Notice how the pressure inside pushes outwards in all directions!

Summary

• Force is a push or pull that can change motion or shape.
• Pressure is force applied per unit area.
• Both force and pressure are important in our daily life and in science.

Practice Questions

1. Define force and give two examples.
2. What is the unit of pressure?
3. Why do sharp objects cut better than blunt ones?
4. Name two types of non-contact forces.
5. How does water pressure change with depth?

Challenge Yourself

• Explain why a camel’s feet are wide and padded.
• Calculate the pressure if a force of 50 N is applied on an area of 2 m².

Did You Know?

• Atmospheric pressure at sea level is about 101,325 Pa!
• Magnetic force can act even through air and some materials.

Glossary

• Force: A push or pull on an object.
• Pressure: Force applied per unit area.
• Contact Force: Force that acts when objects touch.
• Non-contact Force: Force that acts without touching.
• Pascals (Pa): Unit of pressure.

Answers to Practice Questions

1. Force is a push or pull. Examples: kicking a ball, pulling a door.
2. Pascals (Pa).
3. Sharp objects have a small area, so they create more pressure and cut better.
4. Gravitational force, magnetic force.
5. Water pressure increases as depth increases.

---

Explore force and pressure in your daily life and see science in action!