Density describes how much mass is packed into a given volume. To collect data for density:

1. Measure the mass of an object using a beam balance or scale
2. Measure the volume of the object:
   • For regular solids: measure length, width, and height, then multiply
   • For irregular solids: use water displacement in a measuring cylinder
3. Record all values in a table

Example: Measuring density of a stone

After collecting data, we analyse it by calculating and comparing values.

Step 1: Calculate density using the formula

$\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

For the stone above:

$\text{Density} = \frac{150\text{ g}}{60\text{ cm}^3} = 2.5\text{ g/cm}^3$

Step 2: Compare with known values

We can compare our result with standard densities:

Our stone (2.5 g/cm³) has the same density as glass.

Force is a push or pull. We collect force data using a spring balance:

1. Attach the object to the hook of the spring balance
2. Read the scale where the pointer stops
3. Record the force in newtons (N)

Example data collection:

The force needed to lift the sand is 5 newtons.

We analyse force data by comparing measurements:

• The weight of the sand alone = weight of filled box − weight of empty box
• $7\text{ N} - 2\text{ N} = 5\text{ N}$

This shows that force can be calculated by subtracting known values when direct measurement is difficult.

Pressure is the force acting per unit area. To collect pressure data:

1. Measure the force applied (using a spring balance)
2. Measure the area over which the force acts
3. Record both values

Example: Pressure of a wooden block

Calculate pressure using the formula:

$\text{Pressure} = \frac{\text{Force}}{\text{Area}}$

For the wooden block:

$\text{Pressure} = \frac{30\text{ N}}{50\text{ m}^2} = 0.6\text{ Pa}$

Comparing pressures:

If we place the same block on a smaller side (5 m × 4 m = 20 m²):

$\text{Pressure} = \frac{30\text{ N}}{20\text{ m}^2} = 1.5\text{ Pa}$

The pressure is greater on the smaller area. This explains why a sharp knife cuts better than a blunt one—the same force acts on a smaller area, creating higher pressure.

1. Identify the physical quantity you want to explain
2. Select appropriate measuring tools
3. Measure and record data in a table
4. Calculate using the correct formula
5. Compare results with known values or other measurements
6. Draw conclusions about what the data shows

In Tanzania, farmers and builders use these concepts daily. When constructing a house, a builder calculates pressure to ensure the foundation can support the walls—spreading the force over a larger area reduces pressure and prevents the soil from sinking. Similarly, when transporting grain in sacks, knowing the density helps estimate how much can fit in a truck without overloading it.