Chapter 1: Exploration – Entering the World of Secondary Science
Introduction to Secondary Science
In middle school, science mainly introduced basic facts, simple observations, and easy experiments.
In Class 9, science becomes more advanced. Instead of only learning "What happens?", you will also learn:
- Why does it happen?
- How do scientists know it is true?
- How can we test an idea?
- How can science predict future events?
Science is not just a subject to memorize. It is a way of thinking that helps us understand the natural world through evidence and logical reasoning.
What is Science?
Science is based on facts, not opinions or guesses.
Scientists collect evidence, perform experiments, analyze results, and then draw conclusions.
Characteristics of Science
Science is:
- Evidence-based
- Logical
- Systematic
- Testable
- Repeatable
- Always open to improvement
One important feature of science is that scientific knowledge can change if new evidence is discovered.
Curiosity
Definition:-Curiosity is the desire to know, understand, or learn something new.
Curiosity is the starting point of every scientific discovery.
Whenever we ask questions like:
- Why is the sky blue?
- Why do stars twinkle?
- Why does rain fall?
- Why do leaves appear green?
we are thinking scientifically.
Scientific Thinking Process
Curiosity,Observation,Question,Experiment,Evidence,Reasoning,Conclusion,New Discovery
Real-Life Examples of Curiosity
- Why does ice float on water?
- Why does a rainbow appear after rain?
- Why do birds fly?
- Why do objects fall to the ground?
Every scientific invention started with a simple question.
Observation
Definition:-Observation is the careful study of an object or event using our senses or scientific instruments.
Observation is the first practical step in science.
Scientists observe carefully before making any conclusion.
Types of Observation
Normal Observation
- Casual
- No measurements
- Personal opinion may affect the result
Scientific Observation
- Careful and systematic
- Uses measurements
- Recorded properly
- Can be repeated by others
Example
Seeing that dark clouds are forming before rainfall is an observation.
Measuring temperature, humidity, and wind speed before rainfall is scientific observation.
Example 1.1 – Cricket Ball
Suppose a batsman hits a cricket ball.
The question is:
Will the ball cross the boundary?
A simple guess is not scientific.
Scientists consider many factors before making a prediction.
These include:
- Speed of the ball
- Direction
- Angle of projection
- Gravity
- Air resistance
- Wind
- Spin of the ball
Considering these factors gives a much more accurate prediction.
Scientific Models
The real world is often too complex to study directly.
Scientists simplify complicated systems by creating models.
Models help us understand ideas more easily.
Why do Scientists Use Models?
Scientists cannot study every detail at the same time.
They first focus on the most important factors.
Later, more details are added to improve accuracy.
Examples of Scientific Models
- Globe → Model of Earth
- Solar system model
- Atom model
- Cell model
- Human skeleton model
These models represent real objects in a simplified form.
Activity 1.1
Imagine you want to estimate the time taken to travel from school to home.
Important factors:
- Distance
- Walking speed
Factors that can usually be ignored:
- Number of people on the road
- Shops along the way
- Colour of buildings
Ignoring unnecessary details makes the model simple and useful.
Science Uses a Special Language
Scientists across the world use common symbols, units, equations, and mathematical expressions.
This allows scientists from different countries to understand each other's work.
Examples:
- Mass = m
- Velocity = v
- Force = F
- Time = t
- Distance = d
Using symbols makes scientific communication clear and universal.
Important Keywords
| Term | Meaning |
|---|---|
| Science | Systematic study of nature |
| Curiosity | Desire to learn |
| Observation | Careful study |
| Scientific Model | Simplified representation of reality |
| Evidence | Proof collected through observation or experiment |
| Prediction | Expected result based on scientific knowledge |
Science Has Its Own Language
Just like every country has its own language, Science also has a universal language that is understood by scientists all over the world.
This language includes:
- Symbols
- Units
- Formulae
- Equations
- Graphs
- Scientific Terms
Using a common language helps scientists communicate their ideas accurately without confusion.
Why Does Science Need a Special Language?
Imagine if every scientist used different words for the same quantity.
For example:
One scientist writes Speed
Another writes Velocity
Another writes Motion Rate
This would create confusion.
Therefore, scientists use standard symbols and units.
Common Scientific Symbols
| Physical Quantity | Symbol |
|---|---|
| Mass | m |
| Length | l |
| Time | t |
| Distance | d |
| Velocity | v |
| Speed | v |
| Force | F |
| Energy | E |
| Temperature | T |
| Current | I |
These symbols are accepted internationally.
Role of Mathematics in Science
Mathematics is called the language of science because it helps scientists describe nature accurately.
Without mathematics, science would become based only on guesses.
Mathematics helps to:
- Measure quantities accurately.
- Compare observations.
- Make calculations.
- Develop scientific formulas.
- Predict future events.
- Explain natural phenomena.
Example 1: Speed
Instead of saying,
"The car is moving very fast."
Science uses numbers.
Speed = Distance ÷ Time
Now the speed can be measured and compared accurately.
Example 2: Force
Newton's Second Law
Force = Mass × Acceleration
This mathematical equation helps calculate force exactly.
Measurement in Science
Measurement means comparing an unknown quantity with a fixed standard quantity.
Example
Suppose a pencil is 15 cm long.
Here,
Unknown quantity → Pencil length
Standard unit → centimetre (cm)
Measured value → 15 cm
Why Are Measurements Important?
Accurate measurements are necessary because they help scientists:
- Perform correct experiments.
- Compare results.
- Avoid mistakes.
- Share information worldwide.
Even a small measurement error can lead to incorrect conclusions.
Standard Units
Different countries once used different units for measuring the same quantity.
For example,
Length was measured using:
- Handspan
- Foot
- Arm length
- Cubit
These measurements were different for different people.
Therefore, scientists introduced standard units.
SI System of Units
The internationally accepted system of measurement is called the SI System (International System of Units).
Almost every country uses SI Units.
Using SI units ensures that scientific measurements remain the same everywhere in the world.
Seven SI Base Units
| Physical Quantity | SI Unit | Symbol |
|---|---|---|
| Length | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Temperature | kelvin | K |
| Electric Current | ampere | A |
| Amount of Substance | mole | mol |
| Luminous Intensity | candela | cd |
👉 Remember: These are the 7 SI Base Units. Every other SI unit is derived from them.
Why Was the Kilogram Redefined?
Earlier, the kilogram was defined using a physical metal cylinder kept in France.
Scientists noticed that over many years, its mass changed by a tiny amount because of dust, cleaning, and environmental effects.
Since science requires perfect accuracy, the kilogram was redefined in 2019 using the Planck Constant, a fundamental constant of nature.
This new definition is much more stable and accurate.
Advantages of SI Units
- Used internationally.
- Easy to understand.
- Accurate.
- Universal.
- Avoids confusion.
- Makes scientific communication easier.
Scientific Equations
Science uses equations to express relationships between quantities.
Example:
Speed = Distance / Time
Instead of writing a long sentence, scientists use a short equation.
Advantages:
- Easy to remember.
- Accurate.
- Universal.
- Saves time.
- Reduces confusion.
Important Example from NCERT
Airplane Fuel Example
Different countries once used different measurement systems.
One country measured fuel in litres.
Another used gallons.
Because of incorrect unit conversion, the aircraft received much less fuel than required.
As a result, the airplane faced a serious emergency during flight.
Lesson
Science depends on correct units and accurate measurements.
Even a small mistake in units can lead to major accidents.
Key Terms
| Term | Meaning |
|---|---|
| Measurement | Comparing a quantity with a standard unit |
| SI Units | International System of Units |
| Standard Unit | Fixed internationally accepted unit |
| Symbol | Short scientific notation for a quantity |
| Formula | Mathematical relationship between quantities |
| Equation | Statement showing equality between two expressions |
Exam Booster
Q1. Why is mathematics called the language of science?
Answer: Mathematics helps scientists measure quantities accurately, express scientific laws, perform calculations, and make predictions. Therefore, it is called the language of science.
Q2. What is measurement?
Answer: Measurement is the process of comparing an unknown quantity with a standard unit.
Q3. What are SI Units?
Answer: SI Units are internationally accepted standard units used for scientific measurements all over the world.
Q4. Why are standard units important?
Answer: Standard units ensure accuracy, avoid confusion, allow comparison of results, and make scientific communication possible worldwide.
Prediction in Science
Science does not predict by guessing. Every prediction is based on facts, experiments, and mathematical calculations.
Key Idea
Prediction = Observation + Data + Scientific Laws + Calculations
Example 1: Weather Forecast
Weather scientists collect information about:
- Air temperature
- Air pressure
- Humidity
- Wind speed
- Wind direction
- Cloud movement
- Satellite images
Using computers and mathematical models, they predict whether it will rain, be sunny, or become stormy.
Important Point
Weather forecasts are predictions, not guarantees. Sometimes predictions change because weather conditions also change.
Example 2: Solar Eclipse
Scientists can predict:
- Exact date
- Exact time
- Duration
- Path of the eclipse
This is possible because the motions of the Earth and Moon follow scientific laws.
Scientific Evidence
Definition
Scientific evidence is information collected through observations, experiments, and measurements that supports or rejects an idea.
Evidence is the foundation of science.
Without evidence, an idea cannot become accepted scientific knowledge.
Sources of Scientific Evidence
- Observations
- Experiments
- Measurements
- Scientific instruments
- Repeated testing
Why is Evidence Important?
Evidence helps scientists:
- Test ideas
- Verify results
- Correct mistakes
- Build reliable knowledge
Scientific claims must always be supported by evidence.
Example
Suppose someone says,
"This plant grows faster because of magical energy."
A scientist will ask:
- Where is the evidence?
- Has it been tested?
- Can other scientists repeat the experiment?
Without evidence, the claim cannot be accepted.
Repeated Testing
One successful experiment is not enough.
Scientists repeat experiments many times.
Other scientists also repeat the same experiment.
If similar results are obtained repeatedly, confidence in the conclusion increases.
Why Repeat Experiments?
Because experiments may contain:
- Human errors
- Instrument errors
- Environmental changes
Repeated testing improves accuracy and reliability.
Scientific Theories
Definition
A scientific theory is a well-tested explanation of natural phenomena supported by a large amount of evidence.
A theory is not just a guess.
It is developed after years of careful observations, experiments, and testing.
Important Difference
| Guess | Scientific Theory |
|---|---|
| Personal opinion | Supported by evidence |
| No testing | Repeatedly tested |
| May be wrong | Highly reliable |
| No proof | Strong scientific support |
Example
The Germ Theory of Disease explains that many diseases are caused by microorganisms.
This theory became accepted only after extensive scientific evidence.
Can Scientific Knowledge Change?
Yes.
Science is always open to improvement.
If new and stronger evidence is discovered, scientists modify or improve existing explanations.
This is one of the greatest strengths of science.
Example
Scientists continuously improve weather prediction models as better satellites and computers become available.
Estimation
Sometimes scientists need an approximate value instead of an exact value.
This process is called estimation.
Definition
Estimation is the process of finding an approximate value without making exact measurements.
Example (Rice Grains)
Suppose you want to estimate the number of rice grains in a large bag.
Instead of counting every grain:
- Count grains in 100 g.
- Measure the total mass of the bag.
- Calculate the approximate number of grains.
This saves time while giving a reasonably accurate answer.
Breathing Rate Example
Doctors often estimate a person's breathing rate by counting breaths for one minute.
This simple measurement helps assess health conditions.
Breathing rate is an example of how careful observation and measurement are used in daily life.
Scientific Models Improve with Time
Scientific models are not permanent.
As scientists collect more evidence, they improve existing models.
For example:
- Better weather prediction models
- Improved atom models
- More accurate climate models
Science keeps improving as knowledge grows.
Key Characteristics of Science
Science is:
✔ Evidence-based
✔ Logical
✔ Objective
✔ Testable
✔ Repeatable
✔ Self-correcting
✔ Always improving
Important Keywords
| Term | Meaning |
|---|---|
| Prediction | Forecast based on scientific knowledge |
| Scientific Evidence | Information collected through experiments and observations |
| Scientific Theory | Well-tested explanation supported by evidence |
| Estimation | Approximate calculation |
| Verification | Confirming results through repeated testing |
Quick Revision
✅ Science predicts future events using evidence and mathematics.
✅ Weather forecasts are scientific predictions.
✅ Scientific evidence comes from experiments and observations.
✅ Scientific theories are supported by strong evidence.
✅ Repeated experiments increase reliability.
✅ Science continuously improves when new evidence becomes available.
Exam Booster
Q1. What is scientific evidence?
Answer: Scientific evidence is information obtained through observations, experiments, and measurements that supports or rejects a scientific idea.
Q2. What is prediction in science?
Answer: Prediction is forecasting future events based on scientific knowledge, observations, evidence, and calculations.
Q3. Why are experiments repeated?
Answer: Experiments are repeated to verify results, reduce errors, and improve reliability.
Q4. What is a scientific theory?
Answer: A scientific theory is a well-tested explanation of natural phenomena supported by a large amount of scientific evidence.
Branches of Science
Science is divided into different branches because the natural world is very vast. Each branch studies a specific area of nature.
A. Physics
Definition
Physics is the branch of science that studies matter, energy, force, motion, light, heat, sound, electricity, and the laws of nature.
What does Physics study?
- Motion of objects
- Force
- Gravity
- Heat
- Light
- Electricity
- Magnetism
- Energy
Daily Life Examples
- Why does a ball fall to the ground?
- How do fans rotate?
- Why do mirrors form images?
- How does electricity light a bulb?
Chemistry
Definition
Chemistry is the branch of science that studies the composition, structure, properties, and changes of matter.
What does Chemistry study?
- Elements
- Compounds
- Chemical reactions
- Acids and Bases
- Metals and Non-metals
- Medicines
- Fertilizers
Daily Life Examples
- Rusting of iron
- Burning of wood
- Digestion of food
- Cooking food
Biology
Definition
Biology is the branch of science that studies living organisms and life processes.
Biology includes
- Plants
- Animals
- Human Body
- Cells
- Genetics
- Microorganisms
Daily Life Examples
- Photosynthesis
- Respiration
- Growth of plants
- Human digestion
Earth Science
Definition
Earth Science studies the Earth, its atmosphere, rocks, oceans, weather, and natural resources.
It helps us understand:
- Earthquakes
- Volcanoes
- Weather
- Climate
- Rocks
- Soil
- Water cycle
Astronomy
Definition
Astronomy is the branch of science that studies celestial bodies such as stars, planets, moons, galaxies, comets, and the universe.
Astronomers study:
- Solar System
- Milky Way Galaxy
- Black Holes
- Nebulae
- Space Exploration
Interdisciplinary Science
Definition
Interdisciplinary Science is the combination of two or more branches of science to solve complex problems.
Today, many scientific discoveries require knowledge from different branches.
Examples
Medical Science
Uses:
- Biology
- Chemistry
- Physics
Environmental Science
Uses:
- Biology
- Chemistry
- Earth Science
Space Science
Uses:
- Physics
- Mathematics
- Computer Science
- Engineering
Biotechnology
Uses:
- Biology
- Chemistry
- Genetics
Why is Interdisciplinary Science Important?
Many real-life problems cannot be solved using only one branch of science.
Scientists work together from different fields to develop better solutions.
Scientific Thinking in Daily Life
Scientific thinking means making decisions based on:
- Evidence
- Facts
- Observation
- Logic
Instead of:
- Rumours
- Blind beliefs
- Social media forwards
- Personal opinions
Example
Suppose a message on social media says:
"This drink cures every disease."
A scientifically minded person will ask:
- Is there scientific evidence?
- Has it been tested?
- Is it approved by doctors?
- Is there research supporting this claim?
Science teaches us not to believe every claim without evidence.
Surgical Mask Example
During disease outbreaks, scientists recommend wearing surgical masks based on scientific studies.
These studies show that masks reduce the spread of infectious droplets.
This recommendation is based on:
- Experiments
- Medical research
- Clinical evidence
It is not based on rumours or guesses.
This example shows how science helps society make informed decisions.
Science and Society
Science improves our quality of life by contributing to:
- Better healthcare
- Clean drinking water
- Electricity
- Transportation
- Communication
- Agriculture
- Space exploration
- Environmental protection
Science affects almost every part of our daily lives.
Important Characteristics of Science
Science is:
✔ Logical
✔ Evidence-based
✔ Objective
✔ Systematic
✔ Testable
✔ Repeatable
✔ Universal
✔ Self-correcting
✔ Always improving
One-Shot Revision
Science
Systematic study of nature based on evidence.
Curiosity
The starting point of every scientific discovery.
Observation
Careful study using senses or instruments.
Model
Simplified representation of a real system.
Measurement
Comparison with a standard unit.
SI Units
Internationally accepted standard units.
Prediction
Forecast based on scientific laws and evidence.
Scientific Evidence
Data collected through observations and experiments.
Scientific Theory
Well-tested explanation supported by evidence.
Interdisciplinary Science
Combination of different branches of science.
Most Important Exam Questions
Very Short Answer (1 Mark)
- Define Science.
- What is Curiosity?
- What is Observation?
- Define Scientific Model.
- What are SI Units?
- What is Measurement?
- What is Prediction?
- What is Scientific Evidence?
- Name any two branches of Science.
- What is Interdisciplinary Science?
Short Answer (2–3 Marks)
- Explain the importance of observation in science.
- Why are scientific models used?
- Explain the role of mathematics in science.
- Why are SI units important?
- Explain the weather forecasting example.
- Differentiate between a guess and a scientific theory.
Long Answer (5 Marks)
- Explain the scientific method with suitable examples.
- Describe the characteristics of science.
- Explain the importance of evidence and repeated experiments.
- Discuss the different branches of science with examples.
- Explain why science is considered a self-correcting process.
Final Chapter Summary
- Science begins with curiosity and careful observation.
- Scientists ask questions, perform experiments, collect evidence, and draw conclusions using logical reasoning.
- Models simplify complex systems, while mathematics and SI units make scientific communication accurate and universal.
- Scientific predictions (such as weather forecasts) are based on data and evidence, not guesswork.
- Science is divided into branches like Physics, Chemistry, Biology, Earth Science, and Astronomy, and many modern discoveries involve interdisciplinary science.
- Most importantly, science teaches us to think critically, question unsupported claims, and rely on evidence rather than assumptions.
