What is a Joule?
A joule (J) is the SI unit of energy, work, and heat. One joule is defined as the amount of energy transferred when:
- A force of 1 newton moves an object 1 meter
- 1 watt of power is applied for 1 second
- 1 coulomb of charge moves through a potential difference of 1 volt
Kilojoules and Conversion
A kilojoule (kJ) is equal to 1000 joules. This unit is commonly used because:
- It's more convenient for expressing larger amounts of energy
- It's widely used in food energy content (nutritional information)
- It's used in thermodynamics and chemistry calculations
Common Energy Values
Some everyday energy measurements:
- Lifting an apple one meter: ~0.001 kJ (1 J)
- Food Calorie (kcal): 4.184 kJ
- AA battery: ~15 kJ
- Daily food intake: ~8400 kJ (2000 kcal)
Applications
Energy conversion is important in:
- Physics calculations
- Chemistry and thermodynamics
- Nutritional science
- Engineering and mechanics