Page 160 - Volt Elevate The World Around Us Book 4

Materials around Us

The world around us is full of different objects. Some are natural like wood, stones,
cotton and water while others are man-made like plastic, glass and steel. Each of these

objects is made of materials that have certain special properties. These properties help
us understand why some materials are used for building houses, others for making

clothes, and still others for cooking or storage. To know this better, let’s learn about
some common properties such as weight, mass and density.

Weight

Weight is the measure of how heavy an object feels. It is the force with which the Earth
pulls everything towards itself due to gravity. This is why when we drop something, it

always falls down. For example, a big stone feels heavier to lift compared to a wooden
block of the same size because the stone has more weight.

Some objects are very light such as feathers or balloons while others are very heavy like
a metal rod or a bag of rice.

Weight can also change depending on where we are. For example, on the moon, objects

weigh less because the moon’s gravity is weaker than Earth’s.

Mass

Mass is the amount of matter or substance present in an object. Unlike weight, mass

never changes, no matter where the object is. For example, if we have a 1 kilogram brick,
it will always have 1 kilogram of mass, no matter where it is taken.

Density

Density tells us how tightly matter is packed inside an object. Objects that are very
dense feel heavier for their size. For example, a small piece of iron may feel heavier than

a larger piece of wood. This is because iron is denser than wood. On the other hand,
objects that are less dense feel lighter even if they are big in size. For example, plastic or
cork is less dense, so they feel light and often float on water.

Density is an important property because it explains why some objects float and others
sink.

Floating and Sinking in Water

When we put different objects in water, we notice that some float on the surface while
others sink to the bottom. This happens because of the relation between the density of

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