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Pressure in solids — KCSE Physics

KCSE Physics · 118 practice questions · 8 syllabus objectives · 8 revision lessons

39 easy40 medium39 hard

Last updated · Aligned to the KNEC KCSE syllabus

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Identify factors affecting pressure and describe the relationship between area and pressure

Define pressure and state its SI unit (pascal), and write the formula P = F/A

Calculate the pressure exerted by a solid object on a surface using P = F/A

Explain everyday applications of pressure (e.g. sharp knives, wide tractor tyres, snowshoes)

Define pressure as force per unit area and state its SI unit (Pascal); convert between Pa, bar and millibar

Apply the formula P = F/A to calculate pressure, force or area in solid-on-surface problems

Explain everyday applications of pressure including wide tyres, many wheels, sharp edges and mattresses

Pressure in solids

Revision Notes

Concise lesson notes for Pressure in solids, written to the KCSE Physics marking standard. Read the first lesson free below.

Understanding Pressure in Solids

Pressure is defined as the force applied per unit area. The formula for pressure (P) is given by:

P = F/A
Where:

  • P = pressure (Pa)
  • F = force (N)
  • A = area (m²)

Several factors affect pressure in solids:

  • Force: An increase in the applied force increases the pressure.
  • Area: A decrease in the area over which the force is applied increases the pressure.

The relationship between area and pressure is inversely proportional. This means that as the area decreases, pressure increases, and vice versa. For example, a sharp object like a nail exerts more pressure than a flat object like a board because the nail has a smaller area of contact.

To illustrate this, consider a scenario where a force of 100 N is applied over an area of 0.5 m²:

  • The pressure exerted would be:
    P = 100 N / 0.5 m² = 200 Pa
    This shows that a smaller area results in higher pressure.

Key points to remember

  • Pressure is force per unit area.
  • Increased force leads to increased pressure.
  • Decreased area results in increased pressure.
  • Pressure is inversely proportional to area.
  • Sharp objects exert more pressure than flat ones.

Worked example

A force of 50 N is applied on an area of 2 m². Calculate the pressure.

  • P = F/A = 50 N / 2 m² = 25 Pa

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More lessons in this topic

Lesson 2: Understanding Pressure in Solids

Objective: Define pressure and state its SI unit (pascal), and write the formula P = F/A

Pressure is defined as the force applied per unit area on an object. It is a measure of how concentrated a force is over a particular area. The formula to calculate pressure is given by:

P = F/A
Where:

  • P = Pressure (in pascals)
  • F = Force applied (in newtons)
  • A = Area over which the force is applied (in square meters)

The SI unit of pressure is the pascal (Pa), which is equivalent to one newton per square meter (N/m²). This means that if a force of one newton is applied uniformly over an area of one square meter, the pressure exerted is one pascal.

Understanding pressure is crucial in various applications, such as engineering and meteorology, where it helps in determining how forces interact with materials and the environment.

  • Pressure is defined as force per unit area.
  • SI unit of pressure is pascal (Pa).
  • Formula for pressure is P = F/A.
  • 1 pascal equals 1 N/m².
  • Higher pressure results from greater force or smaller area.

Define pressure and state its SI unit.
Pressure is the force applied per unit area. The SI unit of pressure is the pascal (Pa).

Lesson 3: Calculating Pressure from a Solid Object

Objective: Calculate the pressure exerted by a solid object on a surface using P = F/A

Pressure is defined as the force exerted per unit area. The formula for calculating pressure is P = F/A, where:

  • P is the pressure (in Pascals, Pa)
  • F is the force applied (in Newtons, N)
  • A is the area over which the force is applied (in square meters, m²)

To calculate the pressure exerted by a solid object, follow these steps:

  1. Measure the force applied by the object (weight).
  2. Measure the area of contact with the surface.
  3. Substitute the values into the formula P = F/A.

For example, if a block weighs 20 N and has a base area of 0.5 m², the pressure can be calculated as follows:

  • F = 20 N
  • A = 0.5 m²
  • P = 20 N / 0.5 m² = 40 Pa Thus, the pressure exerted by the block is 40 Pascals.
  • Pressure is force per unit area, P = F/A.
  • Force is measured in Newtons (N).
  • Area is measured in square meters (m²).
  • Pressure is measured in Pascals (Pa).
  • Always ensure units are consistent when calculating.

A solid cube exerts a force of 30 N on a surface with an area of 0.2 m². Calculate the pressure.

  • P = F/A = 30 N / 0.2 m² = 150 Pa
Lesson 4: Everyday Applications of Pressure

Objective: Explain everyday applications of pressure (e.g. sharp knives, wide tractor tyres, snowshoes)

Pressure is defined as the force applied per unit area. In everyday life, we encounter various applications of pressure that enhance functionality and efficiency. Here are a few examples:

  • Sharp Knives: A sharp knife has a narrow blade, which concentrates the applied force over a small area, resulting in high pressure. This high pressure allows the knife to cut through materials easily.
  • Wide Tractor Tyres: Wide tyres distribute the weight of the tractor over a larger surface area. This reduces the pressure on the ground, preventing the tractor from sinking into soft soil and allowing it to move more easily.
  • Snowshoes: Snowshoes have a large surface area that spreads the weight of the person over a broader area. This reduces pressure on the snow, preventing the person from sinking and allowing for easier movement on snowy terrain.

Understanding these applications helps us appreciate how pressure influences our daily activities and the design of tools and equipment.

  • Pressure is force per unit area.
  • Sharp knives cut better due to high pressure.
  • Wide tyres reduce ground pressure for better mobility.
  • Snowshoes prevent sinking by distributing weight.

Explain how a sharp knife works better than a dull knife. A sharp knife has a narrow edge, creating high pressure when cutting. This allows it to penetrate materials easily, unlike a dull knife which has a wider edge and applies lower pressure.

Sample Questions

Read 3 questions and answers free. Sign up to access all 118 questions with full KNEC-style marking schemes and a personalised study plan.

1
easySHORT ANSWER3 marks

Define pressure in terms of force and area, and explain how the area over which a force is applied affects the pressure exerted by an object. (3 marks)

Answer & marking scheme

Part (a) — 1 mark
Pressure is defined as force per unit area (P = F/A) (1 mk)
Part (b) — 2 marks
As the area increases, the pressure decreases if the force remains constant (1 mk)
This is because pressure is inversely proportional to area (P ∝ 1/A) (1 mk)
2
easySHORT ANSWER2 marks

Identify two reasons why a mattress is designed to distribute weight evenly. (2 marks)

Answer & marking scheme

Part (a) — 2 marks
To reduce pressure points that can cause discomfort during sleep (1 mk)
To support the body properly, preventing misalignment of the spine (1 mk)
3
easySHORT ANSWER4 marks

A cylindrical metal rod weighs 50 N and has a radius of 2 cm. (a) Calculate the area of the circular end of the rod. (2 marks) (b) Determine the pressure exerted by the rod on a flat surface when resting on its end. (2 marks)

Answer & marking scheme

Part (a) — 2 marks
Area = π × radius² = π × (0.02 m)² = 0.00125664 m² (1 mk)
Area ≈ 0.0013 m² (to 2 significant figures) (1 mk)
Part (b) — 2 marks
Pressure P = F/A = 50 N / 0.00125664 m² (1 mk)
Pressure ≈ 39815.5 Pa (to 4 significant figures) (1 mk)
4

List two reasons why using a sharp knife is more effective than a blunt knife when cutting materials. (2 marks)

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Frequently asked questions

What does the KCSE Physics topic "Pressure in solids" cover?

Pressure in solids covers Identify factors affecting pressure and describe the relationship between area and pressure; Define pressure and state its SI unit (pascal), and write the formula P = F/A; Calculate the pressure exerted by a solid object on a surface using P = F/A, and more, all aligned to the official KNEC KCSE Physics syllabus.

How many practice questions are available for Pressure in solids?

HighMarks has 118 Pressure in solids practice questions for KCSE Physics, each with a full marking scheme. The first 3 are free; sign up to access the rest, plus all KCSE mock exams and past papers.

Are these aligned with the KNEC KCSE syllabus?

Yes. Every objective on this page is taken directly from the official KNEC KCSE Physics syllabus. Practice questions match the KCSE exam format and are graded against the standard KNEC marking scheme.

How should I revise Pressure in solids for the KCSE exam?

Start with the revision notes on this page to refresh the core concepts, then work through the practice questions in increasing difficulty. Sign up for HighMarks to get a personalised study plan that adapts to the topics you keep getting wrong, plus mock exams, subject-wide practice, and detailed performance tracking. See pricing.

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