CLASS 6 SCIENCE · CHAPTER 7
These notes follow the chapter’s sequence and explain its central ideas, examples and activities. Read each section, connect it with the textbook observations, and use the quick check to review the main concepts.
Touch can give a rough sense of whether something feels hot or cold, but it cannot provide a reliable numerical measurement. What feels warm to one hand may feel cool to another if the hands have been exposed to different conditions. Therefore, comparing sensations alone can be misleading. Temperature provides a more objective way to describe how hot or cold an object is. A thermometer is used to measure temperature and gives a reading that can be recorded and compared.
Temperature is measured in degrees Celsius (°C) in the activities described in the chapter. The temperature of a body or material can change as it gains or loses heat. A thermometer has a scale, and the reading is determined by the level indicated by its liquid column or display. Read the scale carefully, noting the numbered marks and the smaller divisions between them. When a question gives a temperature, include the unit; saying only “101 degrees,” for example, is incomplete without specifying the scale.
Different thermometers are designed for different purposes. A clinical thermometer is used to measure body temperature, while a laboratory thermometer is used in experiments involving substances. They may have different ranges and construction, so they are not interchangeable in every situation. The textbook explains why a laboratory thermometer should not be used to measure body temperature. Choose the instrument suitable for the task and follow the instructions for handling it. Never use a thermometer that is cracked or damaged.
Before taking a reading, identify the scale and the value of each small division. If the range between two numbered marks is divided into equal parts, determine the value of one division by dividing the temperature difference by the number of intervals. Then count the divisions to the top of the column. Keep your eye level with the reading to reduce viewing errors. Record the value with °C and avoid estimating more precisely than the scale permits.
Handle thermometers gently and follow the teacher’s procedure. A laboratory thermometer should be positioned as directed for the substance being measured, and the bulb should not touch the container if that would distort the reading. Wait for the reading to stabilise where the procedure requires it. Do not assume that a temperature reading is meaningful without knowing which instrument was used and what was measured. Accurate measurements depend on choosing the correct thermometer, reading its scale properly and recording the unit.
Key idea: Touch can give a rough sense of whether something feels hot or cold, but it cannot provide a reliable numerical measurement.
Observe the examples in the chapter, identify the main idea in each section, and connect the concept with the textbook activities. Use accurate terms, explain your reasoning, and review the key ideas before answering questions.