Q1.
Tie the object, say a stone, with a thread and slowly lower it into the measuring cylinder. What do you notice?
Answer
The water level rises — from 50 mL to 55 mL in Fig. 9.19. The stone has pushed aside, or displaced, exactly its own volume of water, so the rise in level is the volume of the stone.
| S.No. | Object | Initial volume (mL) (A) | Final volume (mL) (B) | Water displaced (mL) (B–A) | Volume of the object (cm³) |
|---|---|---|---|---|---|
| 1. | Stone | 50 mL | 55 mL | 5 mL | 5 cm³ |
| 2. | Metal key | 50 mL | 52 mL | 2 mL | 2 cm³ |
| 3. | Any other (glass marble) | 50 mL | 53 mL | 3 mL | 3 cm³ |
Rows 2 and 3 are sample readings — fill in whatever your own objects give. With the mass from Activity 9.3 you can now finish the calculation the chapter sets out:
Density = Mass / Volume
Density = 16.400 g ÷ 5 cm³
Density of the stone = 3.28 g/cm³
Density = 16.400 g ÷ 5 cm³
Density of the stone = 3.28 g/cm³
Why displacement works: Two things cannot occupy the same space at the same time. When the stone goes in, the water that used to be in that space has to move somewhere, and the only place it can go is upward. So the extra height of water holds exactly the same volume as the stone — which is how you find the volume of a body with no regular shape and no formula.
Check it yourself: Lower the stone gently and keep it fully under water without letting it touch the sides. If part of the stone stays above the surface, you measure only the part that is submerged; if water splashes out, your final reading is too low. The volume of the thread is taken as negligible.