Chapter 10: Force and Pressure 💪
A Comprehensive Guide for PSTET Paper-2 (Science)
Chapter Overview
| Section | Topic | PSTET Weightage | Page No. |
|:---:|:---|::---:|:---:|
| 10.1 | Push and Pull - What is Force? | High | 2 |
| 10.2 | Effects of Force | High | 6 |
| 10.3 | Types of Forces (Contact and Non-Contact) | High | 11 |
| 10.4 | Pressure: Concept and Examples | High | 17 |
| Practice Zone | MCQs & Pedagogical Questions | - | 23 |
Learning Objectives 🎯
After studying this chapter, you will be able to:
✅ Define force and distinguish between push and pull actions with examples
✅ Explain the various effects of force on objects—starting, stopping, changing speed/direction, and changing shape
✅ Classify forces into contact and non-contact types with appropriate examples
✅ Differentiate between muscular force, friction, magnetic force, and gravitational force
✅ Define pressure as force per unit area and explain its applications in daily life
✅ Apply pedagogical strategies to teach force and pressure concepts effectively to upper primary students
Pedagogical Link 🔗
For Teachers: This chapter directly aligns with:
Class 8 Science NCERT Chapter 11: "Force and Pressure"
Teaching Tips:
Begin with kinesthetic activities—students push/pull desks, doors, chairs to experience force
Use sports examples (cricket, football, hockey) to explain effects of force
Create a "Force Museum" with stations demonstrating different force types
Use simple experiments like magnets attracting nails to show non-contact forces
Connect pressure concepts to daily life—why school bags have broad straps, why nails are pointed
Section 10.1: Push and Pull - What is Force? 🤔
Introduction
In our everyday life, we see many things moving around us. A ball moves when kicked, a door opens when pushed, a bucket of water comes up when pulled, and a moving bicycle stops when brakes are applied. What causes these movements? The answer is force .
10.1.1 What is Force?
Definition: Force is a push or a pull that changes or tends to change the state of rest or of uniform motion of an object .
Key Points:
It can make an object move from rest
It can stop a moving object
It can change the speed or direction of a moving object
📝 PSTET Note: Force is a vector quantity—it has both magnitude (how much force) and direction (which way it is applied) .
10.1.2 Push vs. Pull: The Two Aspects of Force
Table 10.1: Difference Between Push and Pull
🧠 Think About This: Some actions involve both push and pull. For example, when you open a drawer, you pull it; when you close it, you push it. When kneading dough, you push and pull repeatedly .
10.1.3 Examples of Push and Pull in Daily Life
Table 10.2: Common Push and Pull Actions
| Activity | Push or Pull? | Reason |
|---|---|---|
| Kicking a football | Push | Foot pushes the ball away |
| Throwing a ball | Push | Hand pushes the ball away |
| Closing a door | Push | Hand pushes the door away |
| Opening a door | Pull | Hand pulls the door toward self |
| Drawing water from well | Pull | Rope pulls the bucket up |
| Tug of war | Pull | Each team pulls the rope |
| Pushing a shopping cart | Push | Cart moves away from you |
| Inflating a balloon | Push | Air pushed into balloon |
| Squeezing a lemon | Push | Hand pushes (squeezes) the lemon |
| Stretching a rubber band | Pull | Hands pull the band apart |
🌍 Did You Know? In some actions, we don't realize we are applying force. When you walk, you push the ground backward—the ground pushes you forward (this is Newton's third law of motion) .
10.1.4 Force: Vector Nature
Force has both magnitude and direction, making it a vector quantity .
| Property | Description | Example |
|---|---|---|
| Magnitude | How much force is applied (measured in Newtons) | 10 N, 50 N |
| Direction | The line along which force acts | Towards the right, upward, downward |
Important: If the same force is applied in opposite directions, the effect is different. Pushing a car forward makes it go forward; pushing it backward makes it go backward .
10.1.5 Force as an Interaction
Force always involves an interaction between two objects . This means:
Force cannot exist in isolation
It always requires two bodies
One body applies force, the other experiences force
Examples of Interaction:
| Situation | Objects Interacting | Force Applied By | Force Experienced By |
|---|---|---|---|
| Kicking a ball | Foot and ball | Foot | Ball |
| Hitting a nail | Hammer and nail | Hammer | Nail |
| Lifting a book | Hand and book | Hand | Book |
| Magnet attracting nail | Magnet and nail | Magnet | Nail |
10.1.6 Pedagogical Implications
Section 10.2: Effects of Force 🎯
Introduction
When force is applied to an object, it can produce various effects. Force can change the state of motion of an object—it can make a stationary object move, or make a moving object stop, speed up, slow down, or change direction. Force can also change the shape of an object .
10.2.1 The Five Effects of Force
Table 10.3: Effects of Force with Examples
10.2.2 Detailed Explanation with Examples
A. Force Can Make a Stationary Object Move 🏃
When a force is applied to an object at rest, it can overcome the object's inertia of rest and set it in motion .
Examples:
A football lying on the ground remains at rest until someone kicks it
A car with a broken engine needs to be pushed to start moving
B. Force Can Stop a Moving Object 🛑
When a force is applied opposite to the direction of motion, it can bring a moving object to rest .
Examples:
Applying brakes to a bicycle—the brake pads apply force opposite to motion
Catching a ball thrown toward you—your hands apply force to stop it
C. Force Can Change the Speed of a Moving Object ⚡
Real-life Scenario: In cricket, a fielder pulls his hands backward while catching a ball. This increases the time of impact, reducing the force and allowing the ball to stop gradually without hurting the hands .
D. Force Can Change the Direction of a Moving Object 🔄
When force is applied at an angle to the direction of motion, it can change the object's path .
Examples:
A batsman hitting a cricket ball—the ball's direction changes
In football, players kick the ball to pass it to teammates—direction changes
A car taking a turn—friction between tires and road changes direction
E. Force Can Change the Shape of an Object ⚙️
Force can deform objects. Some deformations are temporary, while others are permanent.
Table 10.4: Shape Changes Due to Force
| Object | Type of Force | Effect | Permanent or Temporary? |
|---|---|---|---|
| Rubber band | Stretching (pull) | Becomes longer | Temporary (returns to original) |
| Sponge | Squeezing (push) | Compresses | Temporary (returns to original) |
| Dough | Pressing and kneading | Flattens, changes shape | Permanent |
| Metal rod | Bending | Curves | Permanent (if bent beyond elastic limit) |
| Plastic bottle | Squeezing | Dents | Temporary or permanent depending on force |
| Clay | Molding | Takes new shape | Permanent |
10.2.3 Real-life Applications of Force Effects
| Effect of Force | Application in Daily Life |
|---|---|
| Starting motion | Pushing a swing to start it; kicking a ball |
| Stopping motion | Brakes in vehicles; catching a ball |
| Changing speed | Accelerator in vehicles (increase speed); brakes (decrease speed) |
| Changing direction | Steering wheel in cars; rudder in ships |
| Changing shape | Pottery (shaping clay); blacksmith shaping metal; kneading dough |
10.2.4 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Demonstration Stations | Set up stations demonstrating each effect of force | Hands-on learning |
| Sports Connections | Discuss how force works in different sports (cricket, football, tennis) | Real-world relevance |
| "What Happens When..." Questions | Pose scenarios and ask students to predict the effect | Critical thinking |
| Shape Change Activity | Students experiment with clay, dough, rubber bands to observe shape changes | Experiential learning |
Section 10.3: Types of Forces (Contact and Non-Contact) 🧲
Introduction
Forces can be classified based on whether the objects applying force are in physical contact with each other or not. This gives us two main categories: contact forces and non-contact forces .
10.3.1 Classification of Forces at a Glance
Table 10.5: Types of Forces
10.3.2 Detailed Study of Contact Forces
A. Muscular Force 💪
Definition: The force applied by the muscles of living organisms (humans and animals) is called muscular force .
Characteristics:
It is a contact force—muscles need to be in contact with the object
Living beings use muscular force for movement and work
Examples of Muscular Force:
📝 PSTET Note: Animals also use muscular force—bullocks pulling a cart, horses pulling a tonga, elephants lifting logs.
B. Frictional Force
Definition: Friction is the force that opposes the relative motion between two surfaces in contact .
Characteristics:
Acts opposite to the direction of motion
Depends on the nature of the surfaces in contact
Rough surfaces produce more friction; smooth surfaces produce less friction
Examples of Friction:
Brakes on vehicles—brake pads create friction with wheels to stop
Writing with a pen—friction between pen and paper allows writing
Ball rolling and stopping—friction with ground slows it down
Lighting a matchstick—friction produces heat to ignite the match
Friction: Friend or Foe?
| Friction as Friend | Friction as Foe |
|---|---|
| Allows us to walk without slipping | Causes wear and tear of moving parts |
| Enables vehicles to stop with brakes | Produces heat—machines may overheat |
| Helps in writing, gripping objects | Wastes energy—machines need more power |
| Helps in lighting matchsticks | Makes movement difficult (need lubrication) |
C. Applied Force
Definition: The force that is applied to an object by a person or another object .
Examples:
Pushing a table
Pulling a drawer open
Kicking a ball
D. Normal Force
Definition: The support force exerted by a surface on an object resting on it, acting perpendicular to the surface .
Example: A book lying on a table—the table pushes upward on the book. This upward force is the normal force.
10.3.3 Detailed Study of Non-Contact Forces
A. Gravitational Force 🌍
Definition: The force of attraction between any two objects in the universe that have mass .
Characteristics:
It is a universal force—acts everywhere
Strength depends on masses of objects and distance between them
Earth's gravity pulls everything toward its center
Examples of Gravitational Force:
Planets orbiting the Sun—Sun's gravity keeps them in orbit
We stay on Earth's surface—gravity holds us
Tides in oceans—caused by Moon's gravity
📝 PSTET Note: Gravitational force was discovered by Sir Isaac Newton when he saw an apple falling from a tree.
B. Magnetic Force 🧲
Definition: The force exerted by a magnet on magnetic materials (like iron, nickel, cobalt) .
Characteristics:
Can attract or repel (like poles repel, unlike poles attract)
Acts without contact
Strongest near the poles of the magnet
Examples of Magnetic Force:
Magnet attracting iron nails—nails move toward magnet without contact
Refrigerator magnets—holding notes on fridge door
Magnetic compass—needle aligns with Earth's magnetic field
Maglev trains—use magnetic force to float and move
C. Electrostatic Force ⚡
Definition: The force between charged objects .
Characteristics:
Can attract or repel (like charges repel, unlike charges attract)
Acts without contact
Created by rubbing certain materials (static electricity)
Examples of Electrostatic Force:
Comb rubbed on hair attracting small paper pieces—comb becomes charged
Balloon rubbed on hair sticking to wall
Clothes sticking together after drying in dryer
Lightning—massive electrostatic discharge in clouds
10.3.4 Comparison: Contact vs. Non-Contact Forces
| Feature | Contact Forces | Non-Contact Forces |
|---|---|---|
| Physical Contact | Required | Not required |
| Examples | Muscular force, friction, normal force | Gravitational, magnetic, electrostatic |
| Distance Effect | Acts only at point of contact | Acts over distance (field) |
| Medium | Requires physical medium | Can act through vacuum |
| Everyday Experience | Pushing, pulling, holding, walking | Falling objects, magnets attracting |
10.3.5 Balanced and Unbalanced Forces
A. Balanced Forces ⚖️
Definition: When two or more forces acting on an object are equal in magnitude and opposite in direction, they are called balanced forces .
Effect: The net force is zero. Balanced forces:
Cannot change the state of motion of an object
Object at rest remains at rest
Object moving with constant velocity continues with same velocity
Example: In a tug of war, when both teams pull with equal force, the rope does not move—forces are balanced .
Other Examples:
A book resting on a table—gravity pulls down, table pushes up equally
A car moving at constant speed on a straight road—engine force equals friction
B. Unbalanced Forces
Definition: When the forces acting on an object are not equal in magnitude and/or not opposite in direction, they are called unbalanced forces .
Effect: The net force is non-zero. Unbalanced forces:
Change the state of motion of an object
Can make a stationary object move
Can change speed or direction of a moving object
Example: In tug of war, when one team pulls harder, the rope moves toward them—forces are unbalanced .
Other Examples:
Kicking a stationary ball—ball moves (unbalanced force)
Applying brakes—bicycle stops (unbalanced force)
10.3.6 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Force Stations | Set up stations demonstrating different force types | Hands-on learning |
| Magnet Exploration | Students explore magnetic attraction/repulsion | Experiential learning |
| Friction Investigation | Compare movement on different surfaces | Scientific method |
| Balanced/Unbalanced Role Play | Students act as forces in tug of war demonstration | Kinesthetic learning |
| Concept Mapping | Create force classification charts | Visual organization |
Section 10.4: Pressure: Concept and Examples 📍
Introduction
Have you ever wondered why a sharp knife cuts better than a blunt one? Why school bags have broad straps? Why nails have pointed ends? The answer lies in the concept of pressure. Pressure helps us understand how force is distributed over an area .
10.4.1 What is Pressure?
Definition: Pressure is the force acting perpendicularly (normally) on a unit area of the surface .
Formula:
Pressure = Force / Area
P = F / AWhere:
P = Pressure
F = Force applied (in Newtons)
A = Area over which force is distributed (in square metres)
Key Point: Pressure depends on two factors:
Force applied—more force means more pressure
Area over which force is distributed—smaller area means more pressure; larger area means less pressure
10.4.2 Units of Pressure
| System | Unit | Symbol | Relation |
|---|---|---|---|
| SI Unit | Pascal | Pa | 1 Pa = 1 N/m² |
| Other Units | Atmosphere | atm | 1 atm = 101,325 Pa |
| Bar | bar | 1 bar = 10⁵ Pa | |
| Pounds per square inch | psi | Commonly used in USA |
📝 PSTET Note: The SI unit of pressure is Pascal (Pa), named after the French scientist Blaise Pascal .
10.4.3 Factors Affecting Pressure
A. Effect of Force
| Force | Area | Pressure | Example |
|---|---|---|---|
| Increases | Constant | Increases | Pressing a drawing pin harder—it goes in deeper |
| Decreases | Constant | Decreases | Pressing lightly—pin doesn't go in |
B. Effect of Area
| Area | Force | Pressure | Example |
|---|---|---|---|
| Smaller | Constant | Higher | Sharp knife cuts easily |
| Larger | Constant | Lower | Blunt knife doesn't cut well |
Table 10.6: Area and Pressure Relationship
10.4.4 Examples of Pressure in Daily Life
A. Increasing Pressure (Small Area, Same Force)
B. Decreasing Pressure (Large Area, Same Force)
10.4.5 Pressure in Liquids
A. Characteristics of Liquid Pressure
Pressure depends on density of liquid—denser liquids exert more pressure
Pressure at same depth is equal in all directions
Demonstration: Take a plastic bottle, make holes at different heights, fill with water. Water shoots out farthest from the bottom hole—showing pressure is highest at the bottom .
B. Formula for Liquid Pressure
P = h × ρ × g
Where:
P = Pressure
h = Height (depth) of liquid column
ρ (rho) = Density of liquid
C. Examples of Liquid Pressure in Daily Life
10.4.6 Atmospheric Pressure
Definition: The pressure exerted by the weight of air in the atmosphere on Earth's surface.
Key Points:
Air has weight—it exerts pressure
Atmospheric pressure decreases with altitude (less air above)
At sea level, atmospheric pressure is about 101,325 Pa (1 atm)
Examples of Atmospheric Pressure:
10.4.7 Pedagogical Implications
| Teaching Strategy | Description | PSTET Focus |
|---|---|---|
| Pressure Hunt | Students find examples of pressure in classroom/school | Observation skills |
| Demonstration | Show nail, drawing pin, knife examples to explain area-pressure relationship | Visual learning |
| Bottle Experiment | Make holes in plastic bottle to show liquid pressure | Hands-on learning |
| Straw Activity | Demonstrate drinking with straw to explain atmospheric pressure | Experiential learning |
| Comparison Charts | Create charts showing high-pressure and low-pressure examples | Visual organization |
Chapter Summary: Key Points for Revision 📝
Quick Revision Table
Practice Zone: PSTET-Style Questions 🎯
Content-Based MCQs
Q1. Force can be defined as:
a) A push only
b) A pull only
c) A push or a pull
d) A change in shape only
Q2. Which of the following is an example of a pull force?
a) Kicking a football
b) Pushing a trolley
c) Drawing water from a well
d) Pushing a door to close it
Q3. When a batsman hits a cricket ball, the force changes the:
a) Speed only
b) Direction only
c) Both speed and direction
d) Shape of the ball
Q4. Which of the following is a contact force?
a) Gravitational force
b) Magnetic force
c) Frictional force
d) Electrostatic force
Q5. The force that opposes the motion of an object is called:
a) Muscular force
b) Frictional force
c) Magnetic force
d) Gravitational force
Q6. The SI unit of pressure is:
a) Newton
b) Joule
c) Pascal
d) Watt
Q7. A sharp knife cuts better than a blunt knife because:
a) It applies more force
b) It has larger area, so more pressure
c) It has smaller area, so more pressure
d) It is made of better material
Q8. School bags have broad straps to:
a) Look fashionable
b) Increase pressure on shoulders
c) Decrease pressure on shoulders
d) Make the bag heavier
Q9. Which of the following is a non-contact force?
a) Muscular force
b) Frictional force
c) Magnetic force
d) Normal force
Q10. A drawing pin has a sharp point so that:
a) It looks good
b) It can be handled easily
c) Pressure is more due to small area
d) Pressure is less due to small area
Pedagogical MCQs
Q11. A teacher brings a sharp knife and a blunt knife to class and demonstrates cutting a vegetable. This activity teaches:
a) Gravitational force
b) Relationship between area and pressure
c) Magnetic force
d) Muscular force
Q12. To explain the concept of "balanced forces," the best classroom activity would be:
a) Showing a video of a rocket launch
b) Demonstrating tug of war with equal teams
c) Reading from textbook
d) Drawing diagrams on board
Q13. A student asks, "Why do we feel pain if someone hits us with a stick but not with a pillow even if the force is same?" The teacher should explain using:
a) Gravitational force
b) Magnetic force
c) Pressure (area of impact)
d) Muscular force
Q14. While teaching non-contact forces, the most effective demonstration would be:
a) Pushing a table
b) Showing a magnet attracting iron nails without touching
c) Walking on different surfaces
d) Kneading dough
Q15. A teacher wants to demonstrate that liquid pressure increases with depth. The best experiment would be:
a) Show a diagram in textbook
b) Take students to a swimming pool
c) Make holes at different heights in a plastic bottle and fill with water
d) Show a video of deep-sea diving
Answer Key with Explanations
Pedagogical Reflection for Teachers 🤔
Think-Pair-Share Activity:
Think: How would you explain to your students why a camel can walk easily on desert sand but a horse would sink?
Pair: Discuss with a colleague how you would set up a "Force and Pressure Discovery Corner" in your classroom with simple experiments.
Share: Design a 15-minute activity to teach the difference between contact and non-contact forces using everyday objects.
NCERT Textbook Linkages 📚
| Class | Chapter | Topic |
|---|---|---|
| Class 8 | Chapter 11 | Force and Pressure |
| Class 9 | Chapter 8 | Motion |
| Class 9 | Chapter 9 | Force and Laws of Motion |
| Class 11 | Chapter 5 | Laws of Motion |
Chapter End Notes
Key Terminology Glossary
Quick Tips for PSTET Aspirants ⚡
✅ Memorize with Mnemonics:
Effects of Force: "My Smart Cat Stops Dancing Suddenly"
Move stationary objects, Speed change, Change direction, Stop moving objects, Deformation/Shape change
Contact Forces: "My Friend Always Nods" = Muscular, Friction, Applied, Normal
Non-Contact Forces: "Go Make Eggs" = Gravitational, Magnetic, Electrostatic
Pressure Formula: "People Feel Anxious" = Pressure = Force / Area
✅ Common Exam Traps:
Weight vs. Mass: Weight is force (gravitational pull); mass is amount of matter
Push vs. Pull: Same action can be both—opening a door can be push or pull depending on design
Friction is necessary: Without friction, we couldn't walk or stop vehicles
Gravity is universal: Not just Earth—all objects attract each other (though weakly)
Pressure depends on area: Small area = more pressure; large area = less pressure
✅ Important Facts:
Force SI unit: Newton (N)
Pressure SI unit: Pascal (Pa)
1 Pa = 1 N/m²
Atmospheric pressure at sea level: ≈ 101,325 Pa
Gravitational acceleration (g): 9.8 m/s² on Earth
Friction is both friend and foe—depends on situation
Sharp objects work by increasing pressure through reduced area
✅ Application-Based Questions:
"Why are building foundations made broad?"
"Why does a drawing pin have a flat head and pointed tip?"
"Why do we use wide tyres in tractors?"
Answer: Large area reduces pressure, prevents tractor from sinking in soft soil
"Why does a camel have broad feet?"
Answer: Large area reduces pressure, prevents sinking in desert sand
Answers to "Check Your Understanding"
[To be filled by student]
📝 Note for Self-Study: After completing this chapter, ensure you can:
Define force and give 5 examples each of push and pull
List and explain all 5 effects of force with examples
Differentiate between contact and non-contact forces with 3 examples each
Explain muscular force, friction, gravitational force, and magnetic force
Define pressure and write its formula
Explain why sharp objects cut better with area-pressure relationship
Give 5 examples of increasing pressure and 5 examples of decreasing pressure in daily life
Describe characteristics of liquid pressure with examples
Explain atmospheric pressure with 2 daily life examples
End of Chapter 10
Next Chapter: Chapter 11 - Friction
Topics Covered: What is Friction, Factors Affecting Friction, Friction as a Necessary Evil, Increasing and Reducing Friction
