Light, Sound and Force Class 3 Notes Science

Light

Imagine you're in a room, and it's super dark because all the doors and windows are closed, and the light bulbs are switched off. In that darkness, you can't see anything—it's like your eyes are taking a nap!

But wait! If you flick a switch and turn on the light, magic happens. Suddenly, you can see everything around you. What made that magic? It's light! Light is like a superhero for our eyes. It helps us see the world.

So, when it's all dark and you can't see a thing, just bring in some light, and voila! You can see the amazing stuff in your room. Light is the secret ingredient that makes everything visible and turns the darkness into a fantastic world of colors and shapes.

Sources of Light

• During the day, the Sun is our primary source of light.
• At night, the Moon and Stars contribute some light to our surroundings.
• An insect, the glowworm, also emits light, adding to the natural sources.

Artificial Sources of Light:

Inside a room where sunlight can't reach, we rely on artificial sources.

• Glowing Electric Bulbs, Burning Candles, Torches, and Lamps help us see in the dark.
• Electric bulbs and candles are examples of artificial sources created by humans.

Luminous Objects:

Things that give off light are known as luminous objects.

• Natural sources like the Sun, Stars, and Glowworms fall into this category.
• Artificial sources such as Electric Bulbs and Candles are also considered luminous objects.

Non-Luminous Objects:

Objects like a Table or a Book do not produce their own light. They are called non-luminous objects because they don't give out light on their own.

Need for Light Indoors:

• When we're inside a room without sunlight, we need artificial sources like electric bulbs, candles, torches, and lamps to see. These artificial sources replace the natural light and make it possible for us to see things in the dark.

Artificial Sources Created by Humans:

Artificial sources of light are inventions made by humans to brighten our surroundings.

These sources play a crucial role in providing light when natural sources are not available.

Shadow

Light travels in straight lines

• Light Traveling in Straight Lines: Light moves in straight lines, creating thin beams of rays.
• Shadow Formation Process: When objects block the path of light, shadows are formed. Shadows are the dark areas that appear behind objects when they prevent light from passing through.
• Sunlight and Shadows: Standing in the sunlight blocks the path of sunlight, leading to the creation of a shadow. Your shadow mimics your shape and appears on surfaces behind you.

Observing Shadows at Different Times:

• Morning:

  • Shadows are longer in the morning.
  • The sun is low on the horizon, causing light to cover a greater distance before reaching the ground, resulting in longer shadows.

• Afternoon:

  • Shadows are shorter in the afternoon.
  • The sun is higher in the sky, making the distance between the object and the shadow shorter.

• Evening:

  • Similar to the morning, shadows are longer in the evening.
  • As the sun descends, the angle of sunlight changes, creating elongated shadows.

Factors Affecting Shadow Length:

The length of shadows depends on the position of the sun in the sky.

Shadows are longest when the sun is low, and shortest when the sun is high.

Shadows throughout the Day

Properties of Shadow

Playing with Shadows

• Shape of the shadow is similar to the shape of the object.
• The size of the shadow can be smaller or bigger than the object.
• Shadows are always black in colour.
• Shadow always forms on the opposite side of the source of the light.

Transparent, Translucent And Opaque Objects

Transparent Substances: Transparent substances are materials that allow light rays to pass through them clearly. Examples include glass, clear plastic sheets, and transparent water.

Use of Transparent Glass:

• In homes, we use transparent glass in window panes to allow sunlight to enter rooms and kitchens, enabling us to see outside.

Spectacles for Clear Vision:

• Spectacles are made of transparent glass or plastic to help us see clearly through them.

Translucent Substances: Translucent substances allow light to pass through them partially. Examples include frosted glass, colored plastic sheets, oiled paper, and light-colored wet handkerchiefs.

Use of Translucent Frosted Glass:

• In areas like bathrooms, where we want light to enter but also desire privacy, we use translucent frosted glass in window panes.

Translucent Window Glass

Opaque Substances: Opaque substances do not allow light to pass through them at all. Examples are wood, rocks, and metals.

Privacy at Night with Curtains:

• At night, when we switch on lights inside our homes, we use curtains made of opaque material (cloth) to cover windows, ensuring privacy by preventing outsiders from seeing inside.

Sound

Producing Sounds:

• We make sounds too! When we talk, laugh, clap, or run, we create sound waves.

Pleasant Sounds:

• Pleasant sounds are those that make us happy or don't bother us.
• Examples include birds chirping, someone singing, and the gentle ticking of a clock.

Unpleasant Sounds (Noise):

• Unpleasant sounds are irritating and can disturb us. These sounds are also known as noise.
• Examples include vehicles honking in traffic, loud music, and factory noises.

Effects of Noise:

• Noise can make us sick and even give us headaches.
• It disturbs our peace and can be harmful to our well-being.

Differentiating Pleasant and Unpleasant Sounds:

• Pleasant sounds bring joy and calmness, while unpleasant sounds create discomfort and irritation.
• Understanding the difference helps us appreciate the sounds that make us happy and address the ones that can be bothersome.

Force

Force is what we use when we want to move something. It's like a magical push or pull that makes things happen.

Pushing Actions:

• When you want to move something away from you, you push it.
• Example: Kicking a football involves giving it a powerful push.

Pulling Actions:

• When you want to bring something closer to you, you pull it.
• Example: Lifting a football with your hands involves a pulling motion.

Everyday Examples:

• Opening a Drawer:

  • You pull a drawer to open it.
  • You push to close it.

• Sports Activities:

  • In cricket, you push a ball with your bat.
  • When picking up a book, you pull it towards yourself.

Definition of Force:

• Any action of pushing or pulling on an object is called force.
• It's the invisible friend that helps us move, lift, and change the position of things.

Force in Daily Tasks:

• Throughout the day, we engage in a variety of activities that involve applying force.
• Whether it's opening doors, playing sports, or handling objects, force is always at play.

Effects of Force

A force can do many things. It causes change. Objects cannot move untill a force is applied. Force helps us to make an object move, slow down, speed up, stop, and change the direction.

Look at the picture. Rehan is throwing the ball using a force. Akash hits the ball and changes the direction of the moving ball. The ball flies and moves towards Ria. Ria catches the ball. She stops the movement of the ball.