Overview: Archimedes Principle and Salty Water
When a solid object is immersed in a liquid, it experiences an upward force known as buoyant force or upthrust. According to Archimedes Principle, this upward force is equal to the weight of the liquid displaced by the object. This experiment investigates how the density of the liquid affects this force by comparing tap water with strongly salty water.
Key Concepts
- Density Factor: Salty water has a higher density than tap water because of the dissolved salt.
- Upthrust Relation: The upthrust ($F_b$) depends on the density of the liquid ($\rho$). Since the density of salty water is higher, the upthrust exerted by salty water is greater than that of tap water.
- Apparent Weight: The apparent weight of a submerged object is its real weight minus the upthrust. Because upthrust is higher in salty water, the apparent weight is lower (the object feels lighter) in salty water compared to tap water.
- Loss in Weight: The loss in weight corresponds directly to the upthrust. Therefore, the loss in weight is greater in salty water.
Comparison: Tap Water vs. Salty Water
| Parameter | Tap Water | Strongly Salty Water |
|---|---|---|
| Density | Lower (~1 g/mL) | Higher (>1 g/mL) |
| Buoyant Force (Upthrust) | Standard | Greater |
| Apparent Weight of Solid | Higher (Heavier) | Lower (Lighter) |
| Loss in Weight | Less | More |
Experimental Inference
The experiment confirms that the weight of the water displaced by the solid is exactly equal to the loss in weight of the solid, regardless of the liquid used. However, because salty water is denser, a given volume of displaced salty water weighs more than the same volume of tap water. Consequently, the solid loses more weight in salty water.
5 Extra Practice Questions
- Q1: Does the volume of displaced liquid change if a solid is fully submerged in tap water vs. salty water?
Ans: No, the volume displaced depends on the volume of the solid, which remains constant. - Q2: Why is it easier to swim in sea water than in a river?
Ans: Sea water is denser, providing greater buoyant force. - Q3: What is the reading of a spring balance if a 100g mass displaces 20g of water?
Ans: 80g (100g – 20g). - Q4: If you add more salt to the solution, what happens to the spring balance reading of a submerged stone?
Ans: The reading decreases further as density and upthrust increase. - Q5: What is a saturated solution?
Ans: A solution in which no more solute (salt) can be dissolved at that temperature.
