Key learning points

1. The pressure in a fluid increases with depth because the weight of fluid above pushes particles closer together.
2. The pressure on an object in a fluid pushes with more force on the lower part of it and causes upthrust.
3. An object floats in water if its density is less than that of water.
4. The density of a material increases with the mass of each particle and the closeness of its particles.
5. Ice is less dense than water as its crystal structure fixes the particles further apart than they are in water.

Keywords

• Pressure - Produced by the forces from particles within a fluid acting on each other or on a surface.

• Particles - Atoms or molecules that make up matter.

• Upthrust - A force acting upwards on an object in a liquid due to pressure differences between the top and bottom surface.

• Density - The mass per unit volume of a substance; a less dense substance will float on top of a more dense one.

Common misconception