Explore density, relative density, and the law of floatation, including buoyant force.
Density = mass/volume. Relative density is the ratio of a substance's density to the density of water, and has no units.
A substance has density 2.5 g/cm³. Find its relative density (water density = 1 g/cm³).
2.5/1=2.5 (no units)
Why does relative density have no units?
Because it's a ratio of two densities, so the units cancel out
The law of floatation states that a floating object displaces a weight of fluid equal to its own weight. Buoyant force is the upward force exerted by a fluid on an object.
Why does a ship made of steel float, even though steel is denser than water?
The ship's overall shape displaces enough water that its weight equals the weight of displaced water, even though the steel itself is denser
What causes the upward buoyant force on a submerged object?
The pressure difference between the bottom and top of the object, since pressure increases with depth
1. A liquid has density 0.8 g/cm³. Find its relative density.
2. What does the law of floatation state?
3. What is buoyant force?
4. Why does an object with relative density greater than 1 sink in water?
5. A solid has mass 50g and volume 20cm³. Find its density.