Density
Density is mass over volume, and it measures not how heavy something is but how tightly packed its matter is. A kilo of lead and a kilo of feathers have the same mass and very different densities; what changes is the room they take. Floating follows from that: what decides is neither weight nor size but whether the density is below water's. A whole log floats just like a splinter, and a steel ship floats because it encloses air and displaces a great deal of water.
Where this sits
- Comes after
- Quantities
- Opens up
- Pressure and floating
Exercises from this rung
Generated by the app, from easiest to hardest
Does a piece of lead float in water?
- No, it sinks
- It depends on the shape
- Yes, it floats
- It depends on the size
Why lead has a density of 11.3 g/cm³ and water has 1, so it sinks. And size does not matter: a whole log floats just like a splinter, because what decides is density, not mass. Shape does matter for a steel ship, which floats because it encloses air.
easierDoes a piece of ice float in water?
- No, it sinks
- It depends on the shape
- It depends on the size
- Yes, it floats
Why ice has a density of 0.92 g/cm³ and water has 1, so it floats. And size does not matter: a whole log floats just like a splinter, because what decides is density, not mass. Shape does matter for a steel ship, which floats because it encloses air.
in between50 cm³ of lead (11.3 g/cm³). What mass?
Answer 565
Why Mass is density times volume: 11.3 × 50 = 565 g. It is the same relation backwards, and it is what lets you weigh something with no scales when you know what it is made of and how much room it takes.
harder