Science is not just about what we know, but how we know it. It includes:
- Turning observations into measurements.
- Using symbols and equations to show patterns.
- Building models to represent complex systems.
- Checking, revising, or discarding ideas.
Scientific Models
- These are simplified ways of looking at real systems that focus on what is most important.
- The natural world is too complex to study in full detail, so models make it manageable.
- Examples from various fields:
- Physics: Representing a moving car as a single point.
- Chemistry: Drawing atoms/molecules as spheres and bonds.
- Biology: Using diagrams of cells to highlight key parts.
- Earth Science: Treating the Earth as a smooth, layered sphere.
- It involves making assumptions and ignoring some details. E.g. neglecting air resistance to study gravity, ignoring individual cells to study the heart as a system.
Meet a Scientist: Meghnad Saha: Simplifying the Stars
- Science often begins by ignoring details.
- When studying light from stars, Meghnad Saha did not model every atom, reaction, or movement.
- He treated stars as hot gases and focused on temperature, pressure, and ionisation to explain the link between a star’s colour and temperature.
Example: A cricket shot
To model if a cricket ball will cross the boundary for a six, it is necessary to choose what to include and what to ignore.
- Ignore details that make no difference. E.g., the brand of the bat, colour of the ball, and grass on the field.
- Include the most important details. E.g., the mass of the ball, and the speed and direction it is hit.
- Ignore smaller effects for a simple model. E.g., air resistance, ball spin, and the seam stitching. Add them later for greater accuracy.
Activity: Let us model
Suppose you ride a bicycle from your school to your home. You want to model the time it takes to go home from school. What details would you keep? What details could you ignore? Suggest why ignoring some details may actually be useful.
Answer:
- Keep details like: Distance from school to home, speed of the bicycle, traffic or road conditions.
- Ignore details like: Colour of the bicycle, clothes you are wearing, type of school bag.
Ignoring unnecessary details makes the model simpler and helps focus only on factors that affect the travel time.
- Science uses everyday words with specific meanings to communicate clearly. E.g. force, work, cell, reaction etc.
- Quantities are represented by symbols and defined units, such as mass (m), velocity (v), force (F), and electric current (I).
- Mathematics is a language that helps think clearly, allowing relationships between quantities to be expressed precisely and tested carefully.
- An equation is a compact statement about how things are related.
- Mathematical expressions describe relationships such as motion (distance, time, and velocity), chemical reaction rates, population growth, or energy changes.
Threads of Curiosity:
Why is the speed of light denoted by 'c'?
- Scientific symbols often come from history and international agreements. E.g. the symbol c (speed of light) comes from the Latin word celeritas (speed).
- It is a physical constant equal to 299,792,458 m/s.
Ready to Go Beyond
Airplane fuel miscalculation:
- A passenger aircraft ran out of fuel mid-flight because fuel density in pounds (lb) per litre was used instead of kilograms (kg) per litre.
- The flight required 22,300 kg of fuel, but the unit error left it about 15,000 litres short.
- The aircraft safely glided to an emergency landing, causing damage but no casualties. This incident highlights the importance of using standard SI units to avoid dangerous conversion errors.
Threads of Curiosity:
Why is a kilogram used everywhere?
- A kilogram represents the same quantity everywhere, ensuring consistency in trade.
- Measurements are based on agreed international standards. Standard units ensure fairness and allow global comparison of scientific results.
Laws, Theories and Principles in science
- Law: It describes a regular pattern observed in nature, often expressed using words or mathematical relationships. E.g. Newton's laws of motion explain the regular pattern of a passenger feeling a sudden jerk when a bus stops.
- Theory: It explains why something happens, based on evidences. E.g. atomic theory explains how molecules are formed.
In science, a theory is not a guess. It is a well-tested explanation supported by evidence.
- Principle: It is a broad idea that helps understand situations. E.g. the principle of conservation of energy helps explain what happens when we climb stairs.
- Scientific ideas change when new evidence is found. So, science is reliable and self-correcting.
- Scientific predictions are based on evidence, laws, theories, and models. Prediction is a key tool for scientific progress and discovery.
- Matching predictions increase confidence in explanations, while mismatches lead to revision and improved understanding.
Example: How do we check predictions?
Varsha told her friend Meghna, "It will rain this afternoon because the clouds look dark". Think of some questions Meghna could ask Varsha to make this prediction scientifically testable.
Answer:
- Meghna could ask questions like:
"What was the condition of sky during the last rainfall?”
“What is the humidity today?”
“What is today's wind speed and direction?”
“Is the temperature dropping like it did before the recent rains?"
- Such questions make the prediction testable rather than relying only on dark clouds.
Pause and Ponder
1. Think of a prediction you or your family made recently (for example, the outcome of a cricket match). Was it based on evidence and reasoning, or mainly on guesswork? How can scientific thinking improve such predictions?
Answer:
- My family predicted that India would win a cricket match. It is based on the team's recent performance and strong players, not just a guess.
- Scientific thinking improves predictions by using facts, past records, and evidence. This makes predictions more accurate and reliable.
Ready to Go Beyond
Why do weather forecasts sometimes go wrong?
- Weather depends on factors such as temperature, pressure, humidity, and wind.
- Forecasts use measurements and models, but small differences in initial conditions can grow and lead to different outcomes. Therefore, weather forecasts are reliable only for short periods.
- Scientific theories have limits and may be revised or rejected when new evidence contradicts them.
- Science relies on evidence, not opinion or belief.
- No scientific theory is final, and this openness to correction drives scientific progress.
Threads of Curiosity: Is eating food harmful during an eclipse?
- This claim is false.
- An eclipse is simply a play of shadows and does not cause significant physical or temperature changes.
- There is no physical, chemical, or biological mechanism that an eclipse makes food harmful.
- A useful scientific strategy is to identify key quantities and make rough estimates before detailed calculations.
- Estimates help check reasonableness, detect errors, build intuition, and develop confidence.
- Science values careful reasoning over precise calculations.
Ready to Go Beyond
How much rice would feed a family of four for a month?
- For a rough estimate, assume an average adult needs 2,000 to 2,500 kcal / day.
- For 4 people: 2200 × 4 = 8800 kcal per day
- 100 g of uncooked rice provides about 360 kcal
- Rice needed per day: 8800 ÷ 360 ≈ 24.4
- So, 24.4 × 100 g = 2440 g ≈ 2.4 kg of rice / day
- For 30 days: 2.4 kg × 30 = 72 kg
- Thus, a family of four needs 70–75 kg of uncooked rice for a month if all their calories came from rice alone.
- This is a reasonable answer—much more than 100 g, and far less than several tonnes.
- This shows how approximate reasoning helps solve everyday problems scientifically.
Example
Estimate how many litres of air you breathe in one day. Start by estimating how many breaths you take per minute, and the volume of one breath. Your aim is not to find an exact answer, but a reasonable estimate.
Answer:
- At rest, a person takes about 12–15 breaths per minute.
- There are 60 × 24 = 1440 minutes in a day.
- Therefore, breaths per day = 12–15 × 1440 = 18,000–22,000 breaths (round to 20,000 breaths / day).
- A typical party balloon holds about 2 litres of air. It takes about 4–5 breaths to fill one balloon.
- So, one breath contains about 2 ÷ 4 = 0.5 litre of air.
- Total air breathed in a day:
20,000 breaths × 0.5 litre = 10,000 litres / day
Checking the Estimate
- A balloon can be filled in about 20 seconds.
- Therefore, about 3 balloons can be filled in a minute.
- Air blown per minute = 3 × 2 litres = 6 litres.
- In one day: 6 × 1440 = 8640 litres
- This is reasonably close to the earlier estimate of 10,000 litres / day, so the estimate makes sense.
Pause and Ponder
2. Describe one situation where an approximate answer is good enough, and one where you would need a very exact value.
Answer:
- Approximate answer: Estimating the time it will take to walk from home to a nearby shop.
- Exact value: The dose of medicine for a patient.
- The scientific branches are not independent, and real-world problems—like climate change, medicine development, or sustainable technologies—require ideas from multiple disciplines combined.
- Science connects naturally with mathematics, technology, arts, and social sciences.
Pause and Ponder
3. Choose a real-life object (maybe a pressure cooker or a mobile phone) or a problem (maybe a traffic jam near your school). Make a sketch listing what kind of ideas from physics, chemistry, biology, earth science, or mathematics are involved. Show how at least two branches of science connect with your example.
Answer:
Ready to Go Beyond
How does a mask really work?
- Solving real problems requires knowledge from multiple branches of science, as seen with masks during the COVID-19 pandemic.
- Physics explains how a mask works through particle motion and electrostatic attraction to trap threats.
- Chemistry explains the properties of the polymer fibres used to make the mask.
- Biology explains the exact size and behaviour of viruses.
- Mathematics is used to model airflow and calculate the overall filtration efficiency of the mask.
- Science is a human activity driven by curiosity, creativity, collaboration, and questioning.
- It advances through asking questions, testing ideas, sharing results, and learning from mistakes.