Why Can't You Trust Your Hand to Tell Temperature?

Your sense of touch cannot reliably tell how hot or cold something is because it depends on what your skin was feeling just before, not the actual temperature of the object. Temperature is the measure of the degree of hotness of a body, and it is a physical quantity that can be measured accurately with an instrument called a thermometer. For example, if you put one hand in cold water and the other in hot water, then place both hands in lukewarm water, each hand will feel a different sensation, even though the water is at one temperature. This happens because our nerves sense relative changes, not absolute values. In real life, this is why you might feel a metal chair colder than a wooden one, even if both are at room temperature. Many students think their hands can tell the exact temperature, but only a thermometer gives a precise measurement.

A clinical thermometer is designed to measure the temperature of the human body. It has a long, narrow glass tube with a bulb at one end containing mercury. The scale on a clinical thermometer usually ranges from 35°C to 42°C. It also has a constriction near the bulb to prevent mercury from falling back quickly, making it easier to read. A laboratory thermometer, used for measuring temperatures in experiments, has a wider range (commonly from -10°C to 110°C) and does not have a constriction. Both types have a capillary tube for mercury expansion and a scale marked in degrees Celsius. Digital thermometers are now preferred because they do not use mercury, which is poisonous if the thermometer breaks. Digital thermometers are safer, easier to read, and give quick results. For example, doctors now often use digital thermometers to check for fever at home or in clinics. Some students confuse the ranges or use a laboratory thermometer for body temperature, which is not safe or accurate.

To correctly measure temperature, you must follow certain steps and precautions. Always make sure the bulb of the thermometer is fully in contact with what you are measuring. For body temperature, place the bulb under the tongue or in the armpit for about one minute. For liquids like water, immerse the bulb without letting it touch the sides or bottom of the container, as this can give a false reading. Always read the scale at eye level to avoid errors due to the angle of viewing (parallax error). After use, clean the thermometer with an antiseptic solution. For example, if you want to measure the temperature of water, hold the thermometer in the middle of the liquid, away from the container's sides, and wait until the mercury column stops rising. Many students make the mistake of shaking the thermometer too hard or reading it at an angle, which can cause incorrect readings.

The normal human body temperature is 37°C, which is equal to 98.6°F. This is the average temperature for a healthy person, but it can vary slightly from person to person and at different times of the day. To interpret thermometer readings, check where the mercury or digital display stops, and compare it to the scale. For example, if the mercury stops at 38°C, it indicates a fever. You can also use a thermometer to compare the temperatures of different objects or the surroundings. For instance, you may find that water from a tap is cooler than water left in the sun. Some students believe that the body temperature is always 37°C, but small variations are normal and not always a sign of illness.