Force and Energy

Pressure - Meaning of pressure as used in science

By the end of the lesson, the learner should be able to:

- Define pressure as the force acting on a unit area
- State the formula: Pressure = Force ÷ Area
- Show interest in understanding how force and area determine pressure

In groups, learners are guided to:

- Carry out an activity using a pencil or nail on a piece of carton to investigate the effect of area on pressure
- Discuss which two factors pressure depends on from the activity
- Discuss the meaning of pressure from observations

What is pressure and what factors does it depend on?

Active Integrated Science Grade 8 pg. 130
Pencil or nail
Piece of carton
Reference books

Observation Oral questions

Force and Energy

Pressure - Pressure in solids

By the end of the lesson, the learner should be able to:

- Describe pressure in solids as the force exerted per unit area on a surface
- Explain how the area of contact affects the pressure exerted by a solid
- Appreciate that the same force exerts more pressure on a smaller area

In groups, learners are guided to:

- Discuss how a rectangular block exerts different pressures depending on which face rests on the surface
- Study Figure 3.16 showing a block exerting more pressure in position A than position B
- Describe pressure in solids based on observations in Activity 3

How does the area of contact affect the pressure exerted by a solid?

Active Integrated Science Grade 8 pg. 131
Rectangular blocks
Sand or soft clay
Reference books

Observation Oral questions Written tests

Force and Energy

Pressure - Pressure in liquids: variation with depth

By the end of the lesson, the learner should be able to:

- Describe how pressure in liquids varies with depth
- Explain why pressure in a liquid increases with depth
- Show interest in investigating pressure in liquids experimentally

In groups, learners are guided to:

- Carry out an activity using a bottle with holes at different heights to show how depth affects water pressure
- Observe through which hole water jets land farthest and discuss the relationship between depth and pressure
- Study Figure 3.18 showing water jets from holes at different depths

How does depth affect the pressure in a liquid?

Active Integrated Science Grade 8 pg. 133
Plastic bottle
Holes at different heights
Water
Basin

Observation Oral questions

Force and Energy

Pressure - Pressure in liquids: effect of density and communicating tubes

By the end of the lesson, the learner should be able to:

- Describe how the density of a liquid affects the pressure it exerts
- Explain the principle of communicating tubes using the example of water at the same level
- Appreciate the application of pressure in liquids in everyday tools and systems

In groups, learners are guided to:

- Carry out an activity comparing pressure in water and kerosene at the same depth using Figure 3.21
- Study the communicating tubes in Figure 3.20 and discuss why water settles at the same level
- Discuss the application of communicating tubes in plumbing and water level indicators

How does the density of a liquid affect the pressure it exerts at a given depth?

Active Integrated Science Grade 8 pg. 134
Communicating tubes
Water
Kerosene
Funnel

Observation Oral questions Written assignments

Force and Energy

Pressure - Pressure in liquids acts in all directions

By the end of the lesson, the learner should be able to:

- Describe that liquid pressure acts equally in all directions at the same depth
- Demonstrate that liquid pressure acts in all directions using a funnel and rubber sheet
- Show interest in using experiments to verify properties of liquid pressure

In groups, learners are guided to:

- Carry out an activity using a funnel with a rubber sheet stretched over its mouth submerged in water
- Observe the rubber sheet bowing equally regardless of the direction the funnel faces
- Study Figure 3.24 showing pressure acting in all directions in a liquid

Why does pressure in a liquid act equally in all directions at the same depth?

Active Integrated Science Grade 8 pg. 135
Funnel
Rubber sheet
Water
Beaker

Observation Oral questions

Force and Energy

Pressure - Pressure in liquids: horizontal pressure at the same depth

By the end of the lesson, the learner should be able to:

- Describe that liquid pressure at the same depth is equal regardless of horizontal position
- Demonstrate that liquid pressure is equal at the same horizontal level
- Appreciate that the properties of liquid pressure have important practical applications

In groups, learners are guided to:

- Carry out Activity 8 to show that pressure is equal at the same depth in a horizontal direction
- Observe water jets from holes at the same height in Figure 3.23
- Discuss why water from holes at the same depth travels the same horizontal distance

Why is liquid pressure equal at the same depth regardless of horizontal position?

Active Integrated Science Grade 8 pg. 137
Plastic bottle with holes at same height
Water
Basin

Observation Written tests

Force and Energy

Pressure - Calculating pressure in solids

By the end of the lesson, the learner should be able to:

- Apply the formula Pressure = Force ÷ Area to calculate pressure exerted by solids
- Solve worked examples calculating greatest and least pressure of a rectangular block
- Show interest in applying mathematical skills to solve pressure problems

In groups, learners are guided to:

- Study the worked example: rectangular block 15 cm × 6 cm calculating greatest and least pressure
- Solve practice problems on pressure in solids
- Discuss the units of pressure: pascals (Pa) or N/m²

How do we calculate the pressure exerted by a solid on a surface?

Active Integrated Science Grade 8 pg. 138
Worked examples
Reference books
Calculator

Written tests Calculations

Force and Energy

Pressure - Calculating pressure in solids: practice problems

By the end of the lesson, the learner should be able to:

- Solve problems calculating pressure exerted by rectangular and cylindrical solids
- Convert units of area and force correctly when calculating pressure
- Show confidence in solving pressure calculation problems

In groups, learners are guided to:

- Solve problems in the Checkpoint: rectangular block of concrete 3.6 N and cylindrical block 77 g
- Calculate pressure for a rectangular stone block 32 cm × 25 cm × 20 cm
- Peer-check calculations and discuss common errors

How do we apply the pressure formula to solve problems involving solids of different shapes?

Active Integrated Science Grade 8 pg. 139
Calculator
Past exercise books
Reference books

Written tests Calculations

Force and Energy

Pressure - Calculating pressure in liquids

By the end of the lesson, the learner should be able to:

- Apply the formula P = hρg to calculate pressure in liquids
- Solve worked examples on pressure in liquids at given depths
- Show interest in applying the pressure formula to liquid problems

In groups, learners are guided to:

- Study the formula for pressure in liquids: P = hρg where h = depth, ρ = density, g = gravitational field strength
- Solve worked examples calculating pressure at the bottom of a water column
- Solve practice problems on pressure in liquids

How do we calculate the pressure exerted by a liquid at a given depth?

Active Integrated Science Grade 8 pg. 140
Worked examples
Calculator
Reference books

Written tests Calculations

Force and Energy

Pressure - Applications of pressure in solids

By the end of the lesson, the learner should be able to:

- Describe applications of pressure in solids in day-to-day life
- Explain how knowledge of pressure is applied in the design of tyres, cutting tools and shoulder straps
- Appreciate that understanding pressure helps in designing safer and more efficient tools

In groups, learners are guided to:

- Discuss why trucks that carry heavy loads have many wheels
- Discuss why cutting tools are more efficient when sharp
- Discuss why a backpack has broad shoulder straps as shown in Figure 3.29

How is knowledge of pressure in solids applied in the design of everyday tools and equipment?

Active Integrated Science Grade 8 pg. 142
Reference books
Internet access
Charts

Oral questions Written assignments

Force and Energy

Pressure - Applications of pressure in liquids: Pascal's principle

By the end of the lesson, the learner should be able to:

- State Pascal's principle: pressure applied to an enclosed liquid is transmitted equally in all directions
- Describe how Pascal's principle is applied in hydraulic machines
- Appreciate that Pascal's principle enables small forces to lift heavy loads

In groups, learners are guided to:

- Read the information on Pascal's principle and discuss in groups
- Discuss how hydraulic machines such as the hydraulic press and hydraulic jack use Pascal's principle
- Discuss the hydraulic braking system as an application of liquid pressure

How does Pascal's principle explain the working of hydraulic machines?

Active Integrated Science Grade 8 pg. 143
Reference books
Internet access
Charts on hydraulic systems

Oral questions Written tests

Force and Energy

Pressure - Applications: hydraulic press, hydraulic jack and hydraulic braking system

By the end of the lesson, the learner should be able to:

- Describe how the hydraulic press and hydraulic jack use Pascal's principle
- Describe the hydraulic braking system and how it slows down a car
- Show interest in understanding how liquid pressure is used in engineering

In groups, learners are guided to:

- Study the working of the hydraulic press: pushing plunger down transmits pressure to lift a load
- Discuss the hydraulic jack used to lift vehicles in a garage
- Discuss the hydraulic braking system: pressing brake pedal transmits force to brake pads

How do hydraulic machines use Pascal's principle to multiply force?

Active Integrated Science Grade 8 pg. 144
Charts showing hydraulic systems
Internet access
Reference books

Oral questions Written assignments

Force and Energy

Pressure - Calculating pressure in hydraulic systems

By the end of the lesson, the learner should be able to:

- Apply Pascal's principle to calculate forces and pressures in hydraulic systems
- Solve worked examples on hydraulic press calculations
- Show confidence in applying Pascal's principle to solve problems

In groups, learners are guided to:

- Study the worked example: force of 10 N applied on smaller piston, calculate force on larger piston
- Solve practice problems on hydraulic systems using the relationship P₁ = P₂
- Peer-check solutions and discuss common errors

How do we apply Pascal's principle to calculate forces in hydraulic systems?

Active Integrated Science Grade 8 pg. 145
Worked examples
Calculator
Reference books

Written tests Calculations

Force and Energy

Pressure - More applications: pressure in solids and liquids

By the end of the lesson, the learner should be able to:

- Identify and describe additional applications of pressure in solids and liquids
- Explain how pressure principles are used in dams, syringes and water supply systems
- Appreciate the wide range of engineering applications based on pressure

In groups, learners are guided to:

- Use digital or print media to research applications of pressure in solids and liquids
- Discuss how tall dams hold back large volumes of water using liquid pressure principles
- Discuss how syringes use liquid pressure to administer medicine

What are the other ways in which pressure in solids and liquids is applied in our daily lives?

Active Integrated Science Grade 8 pg. 146
Internet access
Reference books
Charts

Oral questions Written assignments

Force and Energy

Pressure - Summative assessment

By the end of the lesson, the learner should be able to:

- Demonstrate mastery of pressure in solids and liquids, Pascal's principle, applications and calculations
- Solve structured and application-based questions covering sub-strand 3.2
- Show confidence in applying knowledge of pressure to real-life situations

In groups, learners are guided to:

- Complete a summative written assessment on sub-strand 3.2
- Discuss assessment answers after marking to consolidate understanding
- Reflect on learning progress across sub-strand 3.2

How well have we mastered the concepts in sub-strand 3.2: Pressure?

Active Integrated Science Grade 8 pg. 146
Assessment papers
Reference books

Written tests Oral questions