An iron block sinks in water but floats in mercury due to the difference in their densities.
Understanding Density and Buoyancy
Density is a measure of how much mass is packed into a given volume. An object will float in a fluid if its density is less than the fluid's density, and it will sink if its density is greater. This is related to the concept of buoyancy, which is the upward force exerted by a fluid that opposes the weight of an immersed object.
Comparing Densities: Iron, Water, and Mercury
According to the provided reference, "the density of mercury [is] higher than iron, while the density of iron is higher than water." This crucial information explains why iron behaves differently in these two liquids.
Density Table:
| Substance | Density (approximate) |
|---|---|
| Water | 1 g/cm³ |
| Iron | 7.87 g/cm³ |
| Mercury | 13.5 g/cm³ |
Note: Densities are approximate and can vary slightly depending on temperature and other factors.
Why Iron Sinks in Water
- The density of iron (7.87 g/cm³) is significantly higher than the density of water (1 g/cm³).
- Because iron is denser, gravity pulls it down with a greater force than the buoyant force of water pushing it up.
- Consequently, the net force on the iron block is downwards, causing it to sink.
Why Iron Floats in Mercury
- The density of mercury (13.5 g/cm³) is significantly higher than the density of iron (7.87 g/cm³).
- In this case, the buoyant force exerted by mercury is greater than the weight of the iron block.
- The net force on the iron block is upwards, resulting in it floating.
Key Takeaways
- An object floats or sinks depending on its density compared to the density of the fluid.
- If an object's density is less than the fluid's density, it floats; if it is greater, it sinks.
- The fact that iron sinks in water but floats in mercury is a direct consequence of these density relationships.
