Exploration: Entering the World of Secondary Science - NCERT Solutions Class 9 Science Exploration

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Exploration: Entering the World of Secondary Science – NCERT Solutions Class 9 Science Exploration includes all the questions with solutions given in NCERT Class 9 Science Exploration textbook.

NCERT Solutions Class 9

English Kaveri Hindi Ganga Sanskrit Sharada Maths Ganita Manjari Science Exploration Social Understanding Society

Entering the World of Secondary Science – NCERT Solutions

Q.1: Think of a cricket ball being hit for a six. You want to make a simple model. What details would you include? What would you ignore?

Solution: We must ask, “Will the ball cross the boundary without hitting the ground first?”. For this, things like the brand of the bat, the colour of the ball, the amount of grass on the field will make no difference. On the other hand, the mass of the ball, and the speed and direction in which it has been hit will be very important. Air resistance, the spin of the ball, and the stitching of the threads at the seam have smaller effects that can be ignored in a simple model. As we build more and more complex models, we add extra details for greater accuracy.

Q.2: 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.

Solution: Good scientific questions will look for measurable evidence and past patterns. Questions with simple yes/no answers are usually not so useful. Meghna could ask Varsha questions like (these are just examples) “What was the condition of sky when it rained the last time? What is the humidity today? Was it above 80 per cent the last time it rained? What is today’s wind speed and direction? Is the temperature dropping like it did before the recent rains?”. Questions like these ask about measurable data and past patterns, which go beyond mere ‘clouds look dark’.

Q.3: 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.

Solution: At rest, we take about 12 - 15 breaths a minute, and there are 60 {tex}\times{/tex} 24 = 1440 minutes in a day, so we take roughly 18 - 22 thousand breaths, about 20 thousand breaths a day. We also need to find the volume of air in one breath. One way to estimate this is to think that it takes about 4 - 5 breaths to fill a typical rubber party balloon, which when inflated has a volume of about 2 litres. So, one breath is perhaps about 0.5 litre. Hence, we breathe in about 10,000 litres of air a day!
Now, it is hard to see if this estimate is reasonable or not. But if we go back to our balloon example, one could blow up a balloon in about 20 s, so maybe we could fill 3 balloons a minute.
Multiplying {tex}\frac{3 \text { balloon }}{\text { minute }} \times \frac{2 \text { litres }}{\text { balloon }} \times \frac{1440 \text { minutes }}{\text { day }}{/tex} will give about 8640 litres, which for estimation purposes is reasonably close to our earlier estimate of 10,000 litres. Naturally, we would get extremely tired very quickly after blowing balloons nonstop, unlike normal restful breathing.

Q.4: Why is the speed of light denoted by ‘c’?

Solution: Scientific symbols often come from history, and are based on international agreements, not necessarily abbreviations of convenience. For example, the speed of light, is usually denoted with the symbol c, since it comes from the Latin word celeritas, meaning speed. Today, the speed of light is one of the physical constants, defined to be exactly 299792458 m/s.

Q.5: Why is a kilogram used everywhere?

Solution: When we buy rice or vegetables we expect a kilogram to mean the same amount everywhere. Imagine the confusion if we used different weights everywhere! Thankfully, measurements are based on agreed international standards, not local objects or opinions. Standard units allow scientific results to be compared, and ensure fairness in daily life and trade.

Q.6: Why do weather forecasts sometimes go wrong?

Solution: Weather depends on many changing factors, such as temperature, pressure, humidity, and wind. Weather forecasts use measurements and models, but very tiny differences in conditions can grow over time and lead to something completely different. This is why forecasts are usually reliable for a few hours or even a few days, but less certain further into the future.

Q.7: How much rice would feed a family of four for a month?

Solution: To make a rough estimate, assume that all their calorie needs come from rice alone. An average adult needs about 2000 - 2500 kilocalories (kcal) per day. Find out how many calories 100 g of uncooked rice provides when cooked and use this to estimate the daily requirement for the family. The aim is not to get an exact number, but to check whether the answer makes sense as 100 g for a month is clearly too little, while a few tonnes is far too much. Such estimation helps connect science to everyday questions about food and resources, and shows why approximate reasoning is an important scientific skill.

Q.8: How does a mask really work?

Solution: Solving real problems requires knowledge from several branches of science. During the COVID-19 pandemic, we all used masks for safety. Understanding how a mask works requires concepts from physics (particle motion and electrostatic attraction), chemistry (properties of polymer fibres), biology (size and behaviour of viruses), and mathematics (modelling airflow and filtration efficiency).