Physics (9-1) - 0972 CIE

Pressure

Overview

A sharp knife slices easily while a blunt one tears, a camel crosses soft sand on its broad feet, and a deep-sea diver feels the water squeeze harder the deeper they go. All three are about pressure: how a force is shared over an area, and how a liquid presses on whatever is beneath its surface.

In this topic you will define pressure, use the equation linking force and area, and explain everyday examples where changing the area changes the effect of a force. You will then look beneath a liquid surface, see qualitatively how pressure grows with depth and density, and use the Supplement equation for the change in pressure in a liquid.

Objectives

Define pressure as force per unit area; recall and use the equation F p = A
Describe how pressure varies with force and area in the context of everyday examples
Describe, qualitatively, how the pressure beneath the surface of a liquid changes with depth and density of the liquid
[Supplement] Recall and use the equation for the change in pressure beneath the surface of a liquid ∆p = ρg∆h

Lesson Note

Pressure decides whether a tool cuts or a tractor sinks, and it sets the loads on dam walls and submarine hulls. In the exam you must define pressure, apply \( p = F/A \) with correct units, and use the liquid pressure equation, so the calculations here earn direct marks.

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Lesson Evaluation

Congratulations on completing the lesson on Pressure. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.

You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.

Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.

A force of 40 N acts on an area of 0.5 m^2. The pressure is: A. 20 Pa B. 80 Pa C. 0.0125 Pa D. 40 Pa Answer: B
The SI unit of pressure is the: A. newton B. joule C. pascal D. watt Answer: C
Pressure beneath a liquid surface increases with: A. depth and density B. width of container only C. surface area only D. colour of the liquid Answer: A
A diver is 10 m deep in water of density 1000 kg/m^3 (g = 9.8 N/kg). The increase in pressure is: A. 980 Pa B. 9800 Pa C. 98000 Pa D. 100 Pa Answer: C
Why does a sharp knife cut more easily than a blunt one? A. it has more mass B. its small edge area gives higher pressure C. it is heavier D. it has lower density Answer: B