Study Notes
Pressure is the force exerted over an area, and it varies depending on whether it is applied to surfaces, within liquids, or gases. Density is the mass per unit volume of a substance and determines whether objects float or sink in a fluid.
- Pressure — the force exerted per unit area. Example: A chair leg on the floor exerts pressure based on its weight and the area of contact.
- Density — mass per unit volume. Example: Water has a density of about 1000 kg/m³, and objects with higher density will sink in it.
- Gas Pressure — the force exerted by gas particles colliding with the walls of their container. Example: Air in a car tire exerts pressure on the tire walls.
- Upthrust — the upward force exerted by a fluid on a submerged object. Example: A floating object experiences upthrust equal to its weight.
Exam Tips
Key Definitions to Remember
- Pressure: Force per unit area.
- Density: Mass per unit volume.
- Upthrust: Upward force by a fluid on an object.
Common Confusions
- Confusing pressure with force; pressure is force per area, not just force.
- Assuming all objects float if they are light; floating depends on density, not just weight.
Typical Exam Questions
- What happens to pressure if the area decreases but force remains the same? Pressure increases.
- How do you calculate the density of an object? Divide its mass by its volume.
- Why does a gas take up more space than a liquid? Because the particles are more spread out.
What Examiners Usually Test
- Calculating pressure and understanding its units.
- Understanding the relationship between density and floating.
- Effects of changing volume on gas pressure.