Buoyancy: Does a Floating Object's Mass Change How Deep It Sits?
1 · Predict
A cork floats in water. If you use a heavier cork of the same size, how will the buoyant force holding it up change?
- The buoyant force increases to match the heavier weight.
- The buoyant force stays the same no matter the mass.
- The buoyant force decreases because the cork sits lower.
2 · Set Up
- Open the fluid-float preset and press Reset. A cork floats at the water's surface.
- Enable the buoyant-force probe on the cork.
- Set the cork's mass for each trial, let it settle to equilibrium, and record the submerged fraction and the buoyant-force reading.
3 · Collect Data
| Cork mass m (kg) | Submerged fraction | Buoyant force F_b (N) |
|---|---|---|
| 1 | ||
| 1.5 | ||
| 2 |
Plot buoyant force F_b (y-axis) against mass m (x-axis) for your three trials. What shape is the line?
4 · Analyze
- For each trial, compute m·g using g = 9.8 m/s² and compare it to the buoyant-force reading.
- Explain why a floating object's buoyant force always equals its weight, regardless of how much of it is submerged.
5 · Extend
- If you kept adding mass to the cork, at what point would it stop floating and sink instead? What would have to be true about the buoyant force at that point?
- A steel block sinks, but a steel ship floats. Using Archimedes' principle, explain how shape — not material — makes this possible.
The Physics Behind This Experiment
Archimedes' Principle
The buoyant force on a submerged (or floating) object equals the weight of fluid it displaces. At equilibrium, a floating object's buoyant force exactly balances its weight — that's why your two columns should match.