10.2. TEMPERATURE AND HEAT

We can begin studying thermal properties of matter with definitions of temperature and heat. Temperature is a relative measure, or indication of hotness or coldness. A hot utensil is said to have a high temperature, and an ice cube is said to have a low temperature. An object that has a higher temperature than another object is said to be hotter. Note that hot and cold are relative terms, like tall and short. We can perceive temperature by touch. However, this temperature sense is somewhat unreliable and its range is too limited to be useful for scientific purposes.

Temperature is essentially how we quantify how hot or cold something is. More simply, when we say an object is hot, it means it has a higher temperature compared to an object that we consider cold. For example, a kettle with boiling water feels hot to us, while an ice cube feels cold. Importantly, these perceptions can vary from person to person, which makes touch an unreliable way of measuring temperature scientifically. Instead, scientists prefer standardized instruments, like thermometers, to measure temperature accurately.

Think of temperature like a game of hide and seek. If you are seeking 'hot' items like boiling water, and you find an ice cube instead, the ice cube would be like someone hiding very well. It isn't what you were expecting. This surprise teaches us that perceptions of temperature can differ and that we need an objective way (like a thermometer) to tell us how hot or cold something truly is!

We know from experience that a glass of ice-cold water left on a table on a hot summer day eventually warms up, whereas a cup of hot tea on the same table cools down. This means that when the temperature of a body, ice-cold water or hot tea in this case, and its surrounding medium are different, heat transfer takes place until they reach the same temperature. We can say that heat is the form of energy transferred between two (or more) systems or a system and its surroundings by virtue of temperature difference.

Heat transfer happens when two objects at different temperatures come into contact. For instance, if you place a cold glass of water on a hot table, the heat from the table will flow to the glass, warming the water. Conversely, if you put hot tea on a cold table, the tea cools down as the heat flows from the tea to the table. This process continues until both the objects reach the same temperature, known as thermal equilibrium. This behavior illustrates how heat naturally flows from hot to cold objects, seeking balance.

Imagine you're at the beach with an ice-cold drink. As you enjoy the sun, the drink warms up. Why? Because it's exchanging heat with the warmer surrounding air. Similarly, when you come back inside from the cold, your hands warm up while touching a hot coffee mug. Here, both your hands and the mug are trying to reach a 'temperature balance', just like people at a party moving towards the best spot in the room!

The SI unit of heat energy transferred is expressed in joules (J), while the SI unit of temperature is Kelvin (K), and degree Celsius (°C) is a commonly used unit of temperature.

In scientific terms, heat energy and temperature are measured using specific units. Heat is measured in joules, which is the standard unit for energy in physics. Temperature is measured in Kelvin and Celsius, whereby Kelvin is primarily used in scientific contexts to avoid negative numbers (as absolute zero is 0 Kelvin). Celsius is more commonly used in everyday life, like weather reports or cooking.

Think of joules as the currency of energy; just like you need money to buy things, you need joules to measure heat. If you were baking cookies, you could say, 'My oven gives off 2000 joules of energy to heat up.' Meanwhile, temperature, whether in Kelvin or Celsius, tells you how 'hot' your oven gets—like saying it’s 350°F or 175°C. It’s all about measuring the energy transfers in cooking, science, or even just enjoying a warm cup of cocoa!

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