3.2 Heat and temperature

• Temperature is the measure of how hot or cold an object is
• Heat is the transfer of thermal energy from one place to another
• Thermal Energy Transfer: Thermal energy can be transferred between objects and stored within them. However, stored thermal energy eventually dissipates into the surroundings. Thermal energy is quantified in joules.
• Particle Vibration and Heat: When the thermal energy of an object increases, its constituent particles vibrate faster, resulting in an overall increase in particle energy. Heat, therefore, represents the total thermal energy stored in the vibrating particles of an object.
• Comparison of Thermal Energy: Consider two glasses of water with equal volumes but different temperatures. The glass containing water at a higher temperature has a greater thermal energy (heat) because its particles are vibrating faster. Despite having the same number of particles, the total thermal energy of the water with higher temperature is higher.
• Volume and Total Thermal Energy: If two glasses of water have the same temperature but different volumes, the glass with the larger volume contains more particles. Consequently, the total thermal energy (heat) of the water with the larger volume is greater, even though both glasses have the same temperature.
• Temperature vs. Heat: Temperature and heat are not the same. Temperature indicates two key aspects: the direction of thermal energy transfer and the average energy of the particles in an object.
• Temperature Difference and Thermal Energy Transfer: Objects with a larger temperature difference transfer thermal energy faster between them. In the example of ice cream at -20 °C and room air at 24 °C, thermal energy transfers from the air to the ice cream due to the 44 °C temperature difference.
• Heat and Particle Energy: Heat provides information about the total energy of particles in an object, while temperature indicates the average energy of the particles. When comparing materials of different sizes or compositions, temperature helps assess the energy levels of their particles.
• Comparison of Temperatures: When comparing the temperatures of different materials, such as hot soup and cold water, it signifies that the average energy of the particles in the hotter substance is greater than that in the colder one. This comparison allows us to understand the relative energy levels of particles in different materials.
• Sparkler Temperature: A sparkler can reach temperatures of about 1000 °C, but individual sparks typically do not cause serious burns due to their small mass and the large temperature difference between the spark and the surrounding air.
• Effect of Particle Number: Sparks have fewer particles compared to the main part of the sparkler, resulting in a significantly lower total particle energy or heat. This means that even though the temperature of a spark is high, its overall thermal energy is small.
• Heat Transfer to Air: The large temperature difference between the spark and the air causes thermal energy to transfer rapidly from the spark to the surrounding air. By the time the spark reaches the skin, its temperature and heat have decreased considerably.
• Absolute Zero: Absolute zero, theorized by Kelvin in the 1800s and defined as -273 °C, is the lowest possible temperature where particles would stop moving entirely. While achieving absolute zero is not feasible, scientists have created temperatures very close to it in laboratory settings.
• 1. Difference Between Heat and Temperature: Heat refers to the total thermal energy in an object, representing the sum of energy from all its particles. Temperature, on the other hand, indicates the average energy of the particles in the object.