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Acids are sour in taste and change the colour of blue litmus to red, whereas, bases are bitter and change the colour of the red litmus to blue.

Whenever a chemical change occurs, a chemical reaction has taken place.

Sound is a form of energy which produces a sensation of hearing in our ears.

Two conditions need to be satisfied for work to be done: (i) a force should act on an object (ii) the object must be displaced. If any one of the above conditions does not exist, work is not done.

A force is needed to change the speed or the direction of motion of an object. An object dropped from a height falls towards the earth. All the planets go around the Sun. The moon goes around the earth.

A force can be used to change the magnitude of velocity of an object (to make the object move faster or slower) or to change its direction of motion. A force can change the shape and size of objects.

Life begins when a single cell divides itself several times to give rise to a large number of cells. These cells gradually form the skin (protection), muscles (movement), bones (support), nerves (control and coordination), and all other organs.

Atoms and molecules are the fundamental building blocks of matter. The existence of different kinds of matter is due to different atoms constituting them.

Ancient Greek philosophers, Democritus and Leucippus suggested that if we go on dividing matter, a stage will come when particles obtained cannot be divided further. Democritus called these indivisible particles atoms.

All living organisms need food. Food supplies proteins, carbohydrates, fats, vitamins and minerals. Both plants and animals are major sources of food. We obtain most of this food from agriculture and animal husbandry.

Mixtures are constituted by more than one kind of pure form of matter. Dissolved sodium chloride can be separated from water by the physical process of evaporation. However, sodium chloride is itself a pure substance and cannot be separated by physical process into its chemical constituents.

Matter is made up of small particles. The matter exists in three states - solid, liquid and gas. The forces of attraction between the particles are maximum in solids, intermediate in liquids and minimum in gases.

While there are billions of planets in the universe, Earth is the only one where life, as we know today, exists and thrives in all its forms.

The living beings are termed as the biotic components and non-living things as the abiotic components of a habitat.

The bright portion of the Moon decreases from a full circle to a half circle in about a week.

Spherical mirrors are a common type of curved mirrors which are shaped like a part of a hollow glass sphere. Mirrors, whose reflecting surfaces are spherical are called spherical mirrors.

When salt and sugar are mixed with water, a uniform mixture is formed, whereas when chalk powder or sand, or sawdust is mixed with water, the components are not evenly distributed. Such mixtures are known as non-uniform mixtures.

When two or more substances are mixed, where each substance retains its properties, it is called a mixture. The individual substances that make up a mixture are called its components.

A constituent particle is the basic unit that makes up a larger piece of a substance or material. The spaces between the particles are known as interparticle spaces.

When we carry a bag, we feel its weight because of the force of gravity acting on our shoulders. The weight of the bag with narrow straps acts on a smaller area of our shoulders, whereas the weight of the bag with broad straps is spread out over a larger area of our shoulders.

In everyday life, we come across many situations where a force is applied, for example, opening a drawer, stretching a rubber band, a fielder stopping a ball, kicking a football, applying brakes on a moving bicycle, rolling a chapati, or turning the steering handle of an auto rickshaw.

When the current flows, the compass needle gets deflected from its original direction. When the current stops, the needle returns to its original direction.

There was a boy called Mario who loved to have lots of friends. He showed off a lot, always talking about how many friends he had at school, and how he was so friendly with everyone.

May my friendships always be
The most important thing to me.

Gajaraj, the elephant, lived in the best booth of the royal stables. The king was fond of Gajaraj, and he had ordered that the elephant should be well looked after.

Mr Raven was perched upon a limb,
And Reynard the Fox looked up at him;
For the Raven held in his great big beak,
A morsel the Fox would go far to seek.

Rama Natha was the son of a rich landlord. His father left him large tracts of land when he died. But Rama Natha did not spend even one day looking after his land.

As per the World Health Organization (WHO), health is defined as a state of complete physical, mental, and social well-being, and not merely the absence of disease.

The human eye can only see objects that are above a certain size. For a long time, many tiny things around us remained unknown.

The Earth spins (or rotates) on its own axis in space. The Earth’s axis of rotation passes through its geographic North Pole and the South Pole. The Earth completes one rotation in about 24 hours.

The Sun gives out or emits its own light and is the main source of natural light on the Earth. Stars, lightning, natural fire, and certain animals also emit their own light.

plants require both sunlight and water for their growth.

Life processes such as nutrition, circulation, respiration, excretion, and reproduction are essential for the survival of living beings. These processes are collectively called life processes.

Humans got interested in keeping track of time long ago. They started noticing that many events in nature repeat themselves after definite intervals of time.

There are three ways in which heat is transferred from one place to another - conduction, convection, and radiation.

The journey of life of a human can be divided into different stages - infancy, childhood, adolescence, adulthood, and old age. Each person experiences these stages at their own pace, and the duration of each stage may vary from one individual to another.

The changes could be in the size, shape, smell, or other property of the substance or object.

Metals are generally hard, lustrous, malleable, ductile, and good conductors of heat and electricity.

Electricity is generated in multiple ways - by windmills, by using wind energy, by solar panels capturing the Sun’s energy, by falling water and by using natural gas or coal. The electric supply from these sources reaches homes and factories via wires.

Substances around us may be classified as acidic, basic, and neutral in nature.

At night, when you look up at the sky, you see many stars. Some stars are bright and others are dim. Stars shine with their own light.

Resources required for our survival are provided by nature. Resources provided by nature are called natural resources. Some important natural resources are air, water, energy from the Sun, forests, soil, rocks, minerals and fossil fuels.

All living beings share some common characteristics. For example, all living beings show movement, they need food, and they grow. They also respire, reproduce, excrete, respond to stimuli, and eventually, die. Absence of any of these features indicates that they are non-living things.

The method of picking by hand from a mixture (when two or more substances are mixed) such as small stones and husk from wheat and rice is called handpicking.

Ice and water are the two forms of the same substance. These forms are also called states. These different states of water show many differences in their behaviour. Water flows but ice does not. Water splashes but ice does not.

Some bodies are hotter than others. For example, during summers, the tap water may be hotter than the cold water from a matka (earthen pot) or a refrigerator. You can realise this by merely touching the two samples of water.

Hand spans and other similar units, such as length of hand, foot, fist or fingers, differ from person to person. Thus, there is a need for such a unit for which measurements of the same length made by different people do not differ.

Any substance that is used to create an object is referred to as material.

The magnets used by sailors in the olden days were based on naturally occurring magnets, known as lodestones which were discovered in ancient times. Later on, people found out that magnets could also be made from pieces of iron.

Food is an essential component of our daily life. India is an agricultural country with diverse soil and climate types. Various crops are grown in its different regions depending on the soil types and climatic conditions.