⚖️ Shortnote: All About Mass!
📦 1. What is Mass?
- The mass of an object is a measure of the amount of matter in the object.
- Grammes (g) and kilogrammes (kg) are two units that are used to measure mass.
- The standard unit of measuring mass is the kilogramme.
Example: A small packet of tea leaves might have a mass of 50 g, while a heavy sack of rice has a mass of 50 kg.
🔬 2. Measuring Instruments
- A balance scale is used to measure the mass of an object by comparing it with the mass of one or more standard weights.
- When the beam of the scale is perfectly horizontal, the scale is balanced.
- Digital scales and indicator scales are used to find exact mass when standard weights cannot be used (like finding your body mass).
Example: If you put a 1 kg standard weight on the left pan and potatoes on the right pan, and the beam is horizontal, you have exactly 1 kg of potatoes!
🔄 3. The Magic Rule & Conversions
1000 g = 1 kg
- To express a mass given in kilogrammes in terms of grammes, multiply the kilogrammes by 1000.
- To express a mass given in grammes in terms of kilogrammes, divide the grammes by 1000.
Example (kg to g): 7 kg = 7 × 1000 = 7000 g.
Example (g to kg): 2750 g = 2000 g + 750 g = 2 kg 750 g.
➕➖ 4. Adding & Subtracting
- Always write the kilogrammes in one column and the grammes in a different column before calculating.
- Adding: If your total grammes reach 1000 or more, carry 1 kg over to the kilogrammes column.
- Subtracting: If you don't have enough grammes to subtract from, borrow 1 kg and turn it into 1000 grammes in the grammes column.
Example Add: 1 kg 500 g + 1 kg 750 g = 2 kg 1250 g → (carry 1 kg) → 3 kg 250 g.
Example Subtract: 3 kg 250 g - 1 kg 500 g → (borrow 1 kg) → 2 kg 1250 g - 1 kg 500 g = 1 kg 750 g.