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Entry competency

Select by clicking the formula you would use to calculate the volume of the regular solid shown below.

Lesson Objectives

By the end of this topic, you should be able to:

- define density
- determine experimentally the densities of substances
- solve numerical problems on density

Volume of a Regular Solid

Volume of a regular solid can be obtained by calculation, using the right formula for the shape of that solid.

For a cube or cuboid (rectangular block or container),

Volume = Length x Width x Height

Volume of Irregular Solid

Volume of an irregular solid can be obtained by displacement method.

Procedure

Water is poured into a measuring cylinder upto a certain level. The volume is read and recorded (V1). Next, the solid is lowered gently into the cylinder till it is completely immersed. The new volume is then noted, say, V2. Volume, V, of the solid is then found from

V = V2 - V1

Observe the next animation and proceed to determine the volume of the irregular solid used.

Did you get the correct answer? The volume of the irregular solid is

Volume of Irregular Solid

The animation shows a piece of sponge dropped into one pan of a beam balance. It is followed by a stone, of nearly the same volume, placed in the other pan. What do you observe?

Volume of irregular solid

The volume of an irregular solid can be measured by the displacement method. First, water is poured into a measuring cylinder upto a certain level. The volume of water is read and recorded (V1). Next, the irregular object is completely immersed (gently) in the water and the the final volume, V2, is recorded. Volume of the irregular object is the found from

V = V2 - V1

In the example that follows, volume of the solid

V = 12.5 cm3.

Density of Solids

In the following animation, a piece of sponge is placed on one pan of a beam balance, followed by a stone on the other pan. Observe what happens.

Observation

Although the stone is about the same size as the sponge, it tilts the balance to its side, implying that it is heavier than the sponge. That is, for equal volumes, stone has a larger mass than sponge.

Activity

Work out the ratio mass : volume (by dividing mass by volume) for each pair of values given. Then enter your results in the third column of a table similar to Table 1.

Table 1

Check your answers against the values given in Table 2.

Table 2

The ratio mass/volume you have entered in the last column is the mass per unit volume. This ratio is called **density****.** *Density is the mass per unit volume of a substance*. It varies from one substance to another. Stone, for example, has a higher density than sponge.

Fill in the spaces by dragging and dropping the correct answers from the list given.

**Conclusion**

The mass and volume of a stone may be different, but the ratio mass/volume of the remains the same.

The ratio mass/volume is the mass per unit volume.

This ratio is called __density__ of the substance.

Density = Mass/Volume.

Type the answer of mass/volume in the last column

The ratio mass/volume is the mass per unit volume

This ratio is called the__ density__ of the substance.

__Exercises__

Fill in the spaces by dragging and dropping answer from the list given

The mass and volume of the stone are different, but the ratio mass/volume remains the same

The ratio mass/volume is the mass per unit volume

This ratio is called the__ density__ of the substance.

Density =Mass/__Volume__

Experiment on Density

Drag the sponge and drop it on one pan of the bean balance. What do you observe? Repeat but drag and drop the stone on the other pan

Select one of the statements in the boxes to describe the relationship between the volume of the sponge and the volume of the stone

Drag the sponge and drop it on one pan of the bean balance. What do you observe? Repeat but drag and drop the stone on the other pan

Density of Liquids

Density of a liquid can be obtained by measuring its volume, V, using a measuring cylinder or burette. The sample is then weighed using a beam balance or compression balance (shown on the previous page) to obtain its mass, M. Density, D, is then calculated from D = M/V.

Density of a substance is characteristic of the substance. No two substances have the same density.

Exercises

How to determine the density of a liquid

**Activity**

Label the apparatus by dragging and dropping the correct label to the apparatus

__Conclusion__

Type the answer of mass/volume in the last column

The ratio mass/volume is the mass per unit volume

This ratio is called the__ density__ of the substance.

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