CBSE Class 3 Science: Light, Sound and Force

• We need light to see the objects around us.
• Sun is the ultimate source of light on Earth.
• We also get light from objects like bulb, torch, candle, lantern, oil lamp and table lamp.
• Luminous Objects: Objects that give light.
• Non-luminous Objects: Objects like table, chair etc that do not give light.
• Transparent Materials: Materials like glass, air etc that allow light to completely pass through them.
• Translucent Materials: Materials like frosted glass and butter paper that allow light to pass through them partially.
• Opaque Objects: Objects like wood, bricks etc that do not allow light to pass through them.
• Rays: The straight lines along which light travels.



• Shadow: A shadow is formed when an opaque object blocks the path of light.


• Our Earth moves around the Sun. And the moon revolves around the Earth.
• Earth and moon do not have light of their own. They receive light from the Sun and reflect the light that falls on them.
• Solar Eclipse: On some new moon days the moon comes in between the Sun and the Earth and blocks the sunlight from falling on Earth. A shadow of the moon is formed on the Earth and people in this shadow region cannot see the Sun either totally or partially, for sometime. Such a phenomenon is called a Solar Eclipse.
• Lunar Eclipse: On some full moon days the Earth comes in between the Sun an the Moon and blocks the sunlight from falling on the Moon. A shadow of Earth is formed on the Moon and thus people cannot see moon (partially or totally) for sometime. Such a phenomenon is called a Lunar Eclipse.
• Sound: We hear different sounds around us. We produce sound when we speak or laugh.
• Pleasant Sounds: Soft sounds that make us happy.


• Noise: Unpleasant sounds that irritate us and make us sick. Unpleasant sounds cause noise pollution.
• We should avoid noise pollution by speaking softly, playing music / TV in low volumes etc.
• We do different types of works in our daily life. For doing work we either push or pull something by applying force on it.
• What is force? The push or pull applied on an object is called force.
• Effects of force:
  1. It can move objects.
  2. It can stop moving objects.
  3. It can change the shape of an object.
  4. It can change the direction of a moving object.