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Different types of solids

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«Физика пәнін ағылшын тілінде оқып үйрену»

Density = mass/volume in symbols, d= m/v
12. Inertia

Different types of solids

Density

In daily usage, iron is said to be “heavier” than wool. This does not mean that an iron nail has more mass than 1m3 wool. What it means is that a piece of iron has more mass than a piece of wool if both have the same volume. In science, when comparing substances, we consider their densities.

Density is defined as the mass in a unit of volume. We calculate the density of matter using the following equation:

Density = mass/volume in symbols, d= m/v

In the SI unit system, mass is measured in kg and volume is measured in m3, thus, the unit of density is kg/m3 (kilogram per cubic meter). But this is inconvenient for most substance, therefore, g/cm3 ( gram per cubic centimeter) is a more common unit of density.

Density is a characteristic property of matter. We can differentiate substances by using their densities. Table 1.7 shows the density of different substances.

Substance	Density (g/cm³)
Helium	0.00018
Hydrogen	0.00009
Oxygen	0.0013
Air	0.0013
Alcohol	0.8
Oil	0.9
Ice	0.9
Water	1.0 (at+4⁰C)
Sugar	1.6
Table salt	2.2
Aluminum	2.7
Iron	7.9
Copper	8.9
Silver	10.5
Lead	11.3
Mercury	13.6
Gold	19.3

The density of copper is 8.9 g/cm3, which means 1 cubic centimeter of copper has a mass of 8.9 g. in other words,8.9 g copper occupies a 1 cm3 volume. (Figure 1.16).

Figure 1.16

12. Inertia

An object that has mass will have a reluctance to change its state of rest or motion. This property is known as inertia. State formally:

Inertia of an object is a tendency of object as rest to remain at rest or tendency of object at motion to remain at motion ay initial direction.

O another definition given by Isaac Newton.

“An object in motion tends to say in motion, and an object at rest tends to stay at rest unless acted upon by an external force.”

The inertia of an object depends on its mass. An object with more mass has greater inertia. In other words, the larger the mass of an object, the harder it is to start moving, show down, move faster of change direction.

A reason that drivers wear seat belts for safety when driving is because of inertia. Without a seat belt, if the driver suddenly applies the brakes, he will continue to move forward due his inertia and crash into the windscreen (figure 1). With a seat belt (figure 2), the driver will be prevented from crashing into the windscreen.

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