Physical Quantities and Measurement
ICSE Class 7 · Physics · Chapter 1
What this chapter covers
- Physical quantities and their units
- Volume and unit volume
- Volume of regular solids
- Measuring the volume of a liquid
- Volume of an irregular solid
- Area of irregular shapes using graph paper
- Density
- Measuring the density of a regular solid
- Speed
- Simple numericals on density and speed
Key definitions
Volume is the amount of space occupied by an object or a substance.
Unit volume is the volume of a cube whose each edge is one unit of length long.
Least count is the smallest volume that can be read on the scale of a measuring vessel, equal to the volume between two neighbouring marks.
Meniscus is the curved surface of a liquid standing in a narrow tube.
Area is the amount of surface enclosed within the boundary of a flat shape.
Density is the mass of a substance contained in a unit volume of it.
Speed is the distance travelled by an object in a unit of time.
Key points
- A physical quantity can be measured and is written as a number with a unit.
- Volume is the space occupied by an object; unit volume is the volume of a cube of edge one unit.
- 1 mL = 1 cm3, 1 L = 1000 cm3 and 1 m3 = 1000 L.
- Volume of a cuboid = l × b × h; volume of a cube = a3.
- A liquid's volume is read on a graduated cylinder or beaker, with the eye level with the bottom of the meniscus.
- The volume of an irregular solid equals the rise in water level when it is fully lowered into water.
- The area of an irregular shape is estimated on graph paper by counting whole squares and squares half or more covered.
- Density = mass ÷ volume, measured in g/cm3 or kg/m3; water's density is about 1 g/cm3.
- Density depends on the substance, not on the size of the piece.
- Speed = distance ÷ time, measured in m/s or km/h.
- Distance = speed × time, and time = distance ÷ speed.
Questions answered
Define volume and name two units in which it is measured.
Volume is the amount of space occupied by an object or a substance. It is measured in cubic metres (m3) and cubic centimetres (cm3); liquids are often measured in litres (L) and millilitres (mL).
What is meant by unit volume?
Unit volume is the volume of a cube whose each edge is one unit of length long, for example 1 cm3 for a cube of edge 1 cm.
How many cubic centimetres make one litre?
1 L = 1000 cm3.
A matchbox is 5 cm long, 4 cm wide and 1.5 cm high. Find its volume.
5 × 4 × 1.5 = 30 cm3.
Why should your eye be level with the liquid surface when you read a measuring cylinder?
Looking from above gives a reading that is too high, and looking from below gives one that is too low. This parallax error is avoided only when the eye is level with the bottom of the meniscus.
Water in a cylinder stands at 25 mL. A key is lowered into it and the level rises to 29 mL. Find the volume of the key.
29 - 25 = 4 mL = 4 cm3.
When estimating area on graph paper, which partly covered squares do you count?
Count a square as one if half or more of it lies inside the outline, and ignore it if less than half lies inside.
A body has a mass of 120 g and a volume of 40 cm3. Find its density.
120 ÷ 40 = 3 g/cm3.