Physical Quantities and Measurement
ICSE Class 6 · Physics · Chapter 2
What this chapter covers
- Physical quantities and units
- Measurement of length
- Measurement of mass
- Measurement of time
- Measurement of temperature
- Measurement of area
- Converting between related units
Key points
- A physical quantity can be measured and is written as a number with a unit.
- Length is the distance between two points; its units include cm, m, km, inch and foot.
- A ruler measures short, straight lengths; a measuring tape measures long or curved lengths.
- Mass is the amount of matter in an object; its units are mg, g and kg.
- A beam balance compares an object with known masses; an electronic balance shows the mass on a screen.
- Time is measured in seconds (s), minutes (min) and hours (h) with a clock, a watch or a stop-watch.
- Temperature tells how hot or cold an object is and is measured in degree Celsius (°C).
- A clinical thermometer measures body temperature; normal body temperature is about 37 °C.
- A laboratory thermometer measures the temperature of other objects and has no kink.
- Area is the surface a flat shape covers; graph paper helps measure it in square centimetres.
- To change a bigger unit to a smaller one, multiply; to change a smaller unit to a bigger one, divide.
Questions answered
What two parts must every measurement have?
A number and a unit, for example 12 cm.
Name the instrument you would use to measure the length of a pencil and the boundary of a round flower bed.
A ruler for the pencil; a measuring tape for the curved boundary of the flower bed.
Why should your eye be straight above the mark when you read a ruler?
Looking from one side makes the mark seem to shift, so the reading comes out wrong.
Give the symbols for milligram, gram and kilogram.
mg, g and kg.
What does the kink in a clinical thermometer do?
It stops the liquid from falling back, so the reading stays steady after the thermometer is taken out.
What is the normal temperature of the human body?
About 37 °C.
Why must a laboratory thermometer be read while its bulb is still in the liquid?
It has no kink, so the reading starts to change as soon as it is taken out.
Change 4 kg into grams and 180 seconds into minutes.
4 kg = 4 × 1000 = 4000 g; 180 s = 180 ÷ 60 = 3 min.