Density and Pressure

Summary and Exam Tips for Density and Pressure

Density and Pressure is a subtopic of Solids, Liquids, and Gases, which falls under the subject Physics in the Edexcel IGCSE curriculum.

Density is defined as the mass per unit volume of a material, expressed by the equation $\rho = \frac{m}{V}$. To determine density, both mass and volume must be known. For liquids, mass is found by weighing the container with and without the liquid, while volume is read from a measuring cylinder. For irregular solids, volume is determined by water displacement in a measuring cylinder. Upthrust is the upward force exerted by a fluid, allowing objects to float if the upthrust equals or exceeds the object's weight. In fluids, a lower density liquid will float on a higher density liquid.

Pressure is the force applied per unit area. It increases with force and decreases with area. For example, a pointed nail exerts more pressure than a rod due to its smaller area. In fluids, pressure is uniform and increases with depth and fluid density. The pressure at the bottom of a fluid column is calculated using $P = \rho \times g \times h$.

Exam Tips

• Unit Conversion: Be adept at converting units, such as meters to centimeters and grams to kilograms. Remember, multiply to convert to smaller units and divide for larger units.
• Density Calculations: Practice calculating density using the formula $\rho = \frac{m}{V}$ and understand how to measure mass and volume accurately.
• Pressure Understanding: Grasp the concept of pressure in both solids and fluids, and practice calculating pressure using $P = \rho \times g \times h$.
• Conceptual Clarity: Ensure you understand the principles of upthrust and how it affects floating and sinking in fluids.
• Practical Examples: Relate theoretical concepts to real-world examples, like why a nail penetrates wood more easily than a rod.