9.1.1 Units of Temperature Explained

Key Concepts

1. Definition of Temperature

Temperature is a measure of the average kinetic energy of the particles in a substance. It indicates how hot or cold an object is.

2. Celsius (°C)

Celsius is a temperature scale where the freezing point of water is 0°C and the boiling point is 100°C at standard atmospheric pressure.

3. Fahrenheit (°F)

Fahrenheit is a temperature scale where the freezing point of water is 32°F and the boiling point is 212°F at standard atmospheric pressure.

4. Kelvin (K)

Kelvin is an absolute temperature scale where 0 K is absolute zero, the lowest possible temperature where particles have no thermal energy. The freezing point of water is 273.15 K, and the boiling point is 373.15 K.

5. Conversion Formulas

To convert between Celsius, Fahrenheit, and Kelvin, use the following formulas:

• Celsius to Fahrenheit: °F = (°C × 9/5) + 32
• Fahrenheit to Celsius: °C = (°F - 32) × 5/9
• Celsius to Kelvin: K = °C + 273.15
• Kelvin to Celsius: °C = K - 273.15
• Fahrenheit to Kelvin: K = (°F + 459.67) × 5/9
• Kelvin to Fahrenheit: °F = (K × 9/5) - 459.67

Detailed Explanation

Definition of Temperature

Temperature is a fundamental property that reflects the thermal state of a substance. It is directly related to the motion of particles within the substance. Higher temperature means faster particle motion, and lower temperature means slower particle motion.

Celsius (°C)

The Celsius scale is widely used in everyday life and scientific contexts. It is based on the properties of water, making it easy to understand and use. For example, room temperature is typically around 20°C, and the temperature of a hot summer day might be around 35°C.

Fahrenheit (°F)

The Fahrenheit scale is commonly used in the United States. It has a more complex relationship with water's freezing and boiling points compared to Celsius. For instance, a comfortable room temperature is about 70°F, and a hot summer day might reach 95°F.

Kelvin (K)

The Kelvin scale is used in scientific contexts because it is an absolute scale, meaning it starts at absolute zero. This makes it useful for calculations involving thermal energy and temperature changes. For example, the temperature of liquid nitrogen is about 77 K, and the temperature of the Sun's surface is about 5,800 K.

Conversion Formulas

Understanding how to convert between different temperature scales is crucial for accurate measurements and comparisons. For instance, if you know the temperature in Celsius and need it in Fahrenheit, you can use the conversion formula to find the equivalent temperature.

Examples and Analogies

Example: Converting Celsius to Fahrenheit

If the temperature is 25°C, to convert it to Fahrenheit, use the formula: °F = (25 × 9/5) + 32 = 77°F. So, 25°C is equivalent to 77°F.

Analogy: Temperature Scales as Different Languages

Think of temperature scales like different languages. Just as you need a translator to understand a sentence in another language, you need conversion formulas to understand temperatures in different scales.

Example: Converting Fahrenheit to Kelvin

If the temperature is 68°F, to convert it to Kelvin, use the formula: K = (68 + 459.67) × 5/9 = 293.15 K. So, 68°F is equivalent to 293.15 K.

Analogy: Kelvin as Absolute Zero

Consider Kelvin as the baseline of a race. Absolute zero (0 K) is the starting point, and every other temperature is measured relative to this point, just like runners in a race are measured from the starting line.