Weight (I): Kilogram

1Summary 重點摘要

1 kg = 1000 g. Adult about 60 kg.

2Vocabulary cards Vocabulary

3Step by step Steps

1. Part 1: Heavy things use kgUse kilograms for heavier things; this is one principle for choosing units: the heavier the thing, the bigger the unit. Example: an adult weighs about 60 kg, a watermelon about 5 kg, and a bag of rice about 8 kg. In grams these become huge numbers, since 60 kg is 60000 g, awkward to read and to write, so kilograms fit better. Take care to think of a familiar object, such as a bag of rice, as a reference before estimating, instead of guessing from nothing.
2. Part 2: Light things use gUse grams for lighter things; very light objects measured in kilograms give tiny numbers that are hard to grasp. Example: a one-dollar coin is about 5 g, a slice of bread about 30 g, and a sweet about 5 g. Very light things must be measured in grams so we can see how light they are and compare them easily. Take care that unit choice follows accuracy and convenience; a coin written as 0.005 kg is hard to understand, but 5 g is clear at once.
3. Part 3: 1 kg = 1000 gKilograms and grams are linked: 1 kg = 1000 g, the heart of weight conversion. Why 1000? The rate between kilogram and gram is fixed at one thousand. Split a 1 kg bag of sugar into 1000 equal parts and each part is 1 g, so there are 1000 grams in 1 kilogram, and this link makes converting possible. Take care that the weight rate differs from length: 1 kg = 1000 g goes by thousands, unlike the hundreds between m and cm, so keep the two systems of units separate in your mind.
4. Part 4: kg to g, multiply by 1000To change kg to g, multiply by 1000, because 1 kg holds 1000 grams. Example: 3 kg = 3 × 1000 = 3000 g, and 4 kg = 4000 g. Going from a bigger unit to a smaller unit makes the number bigger; the smaller the unit, the bigger the number, a rule shared by every conversion. The usual error is multiplying by 100, writing 3 kg as 300 g, which shrinks the number instead; between kg and g stand three zeros, so from kg to g the multiplier is always 1000.
5. Part 5: g to kg, divide by 1000To change g to kg, divide by 1000, the opposite direction from the last step. Example: 5000 g = 5000 ÷ 1000 = 5 kg. If it does not divide exactly, as with 3500 g, write 3 kg with 500 g left over, that is 3 kg 500 g, and the answer is just as correct. Take care that a smaller unit turning into a bigger one should shrink the number; if the number grows after converting, multiply and divide have been swapped, so stop and check at once. Also, the gram part of the mixed form is not a decimal; never write 3.500 kg.
6. Part 6: Using scales and balancesWeights can be measured with digital scales or balances, and the two read in different ways. A digital scale shows the number directly, such as a watermelon weighing a little over 4 kg, while a balance compares two sides for heaviness. Example: put a 4 kg melon and a 5 kg melon on a balance, and the 5 kg side sinks, showing it is heavier. Take care to read whether the scale is set to kg or g before using it; the wrong unit makes the reading out by a thousand times and quite useless.

4Diagrams Diagrams

5Worked example Example

6Common mistakes Mistakes

7Quick check Quick check

8Recap Recap

• 1 kg = 1000 g
• Heavy things (people, melons, rice) use kg; light things use g
• kg to g: multiply by 1000
• g to kg: divide by 1000
• Match units before comparing or adding weights