Whose hand is the unit?
A standard unit means the same thing everywhere.
Ravi and Meera
Ravi and Meera measure the same table in handspans. Ravi’s hand is bigger than Meera’s.
Ravi gets 6 spans. What will Meera get?
What this lesson covers
The idea
Measurements are based on agreed international standards, not on local objects or opinions; standard units allow scientific results to be compared.
Ravi and Meera
Ravi and Meera measure the same table in handspans. Ravi’s hand is bigger than Meera’s.
Ravi gets 6 spans. What will Meera get?
- Also 6
- More than 6
- Fewer than 6
Measure the table
Tap a measurer to lay their hand along the table, then the ruler.
Agree on one unit
Measurements are based on agreed international standards, not on local objects or opinions. Standard units allow scientific results to be compared.
Think of buying rice. A kilogram must mean the same amount everywhere, or trade would not be fair. Science needs the same agreement so results from any lab can be compared.
- Quantity | Standard unit
- length | metre (m)
- mass | kilogram (kg)
- time | second (s)
Notes
Measurements are based on agreed international standards, not local objects or opinions. Standard units let scientists compare results.
Check yourself
Why is a kilogram used everywhere to buy rice?
Ravi says the table is 6 spans. Meera says 8 spans. Who is right?
Which of these is a standard unit of length?
The table is 120 cm long. Arjun’s handspan is 24 cm. How many spans long is the table?
Answer: 5 spans
120 cm ÷ 24 cm = 5 spans. Another hand gives another number, but 120 cm is 120 cm for everyone.
- It is an agreed standard, so a kilogram means the same amount everywhere — correct. Yes. That makes trade fair and results comparable.
- Because rice is heavy. The reason is agreement, not the rice.
- Because each shopkeeper decides his own weight. That would be unfair. Standard units avoid it.
- Meera, because 8 is bigger. Bigger does not mean right. The spans are different sizes.
- Both are right, but their spans are different. To compare, use a standard unit — correct. Yes. A standard unit removes the confusion.
- Ravi, because he is older. Opinion does not decide measurement.
- A handspan. It changes from person to person.
- The metre — correct. Yes. It is agreed internationally.
- A footstep. It changes from person to person.