Bouncing and Blocking Light

Light travels in straight lines, but it can bounce off some things and be stopped by others.

Reading is good — doing is better. Practice Bouncing and Blocking Light as an interactive lesson.

Definition

Light is a kind of energy we can see. When light hits an object, one of two things can happen: it can bounce off (like a ball bouncing off a wall) or it can be blocked and stopped. When light bounces off something, we call that reflection. When something stops light completely, it makes a dark area called a shadow.

Remember the rule

Light travels straight → hits object → BOUNCES (reflects) OR BLOCKS (makes a shadow)!

Key words

Light: Energy that lets us see things around us.
Reflect: When light bounces off a surface and changes direction, like a mirror bouncing light back at you.
Shadow: A dark shape made when an object blocks light from passing through.
Opaque: A word for objects that block all light, like a book or a wooden door.
Transparent: A word for objects that let all light pass right through, like a clear glass window.
Translucent: A word for objects that let some light through but not all of it, like a frosted bathroom window.
Surface: The outside layer of an object that light hits.
Source: Something that makes light, like the sun, a flashlight, or a lamp.

Worked examples

You shine a flashlight at a mirror. What happens to the light?

→ The light bounces off the mirror and travels in a new direction. You might see the bright spot appear on the wall or ceiling nearby. · Mirrors have very smooth, shiny surfaces that are great at reflecting light.

You hold your hand in front of a flashlight. What appears on the wall behind your hand?

→ A dark shape that looks like your hand appears on the wall. That dark shape is called a shadow. · Your hand is opaque, so it blocks the light and stops it from reaching the wall.

You shine a flashlight at a clear plastic water bottle. Does it make a dark shadow?

→ Only a very faint shadow appears because most of the light passes right through the clear bottle. · Clear objects are transparent, so they let light through instead of blocking it.

It is a sunny day. You stand outside. Where is your shadow?

→ Your shadow is on the opposite side of you from the sun. The sun's light hits you, you block it, and a shadow forms behind you. · The shadow moves during the day because the sun moves across the sky.

You put a piece of wax paper in front of a flashlight. What do you see?

→ Some light passes through the wax paper, but it looks dimmer and blurry on the other side. The wax paper only lets some light through. · Wax paper is translucent, not fully transparent and not fully opaque.

You hold a shiny spoon up near a sunny window. You see a bright spot of light on the wall. Why?

→ The smooth, shiny surface of the spoon reflected the sunlight and bounced it onto the wall, making a bright spot. · Any smooth and shiny surface, not just mirrors, can reflect light.

Common mistakes

Thinking shadows are made of something solid. A shadow is just a space where light is missing, not a real object.
Thinking light goes around objects to make a shadow on all sides. Light travels straight, so the shadow only appears on the side away from the light source.
Confusing transparent and translucent. Transparent means ALL light passes through; translucent means only SOME light passes through.
Thinking only mirrors can reflect light. Any smooth or shiny surface, like water, aluminum foil, or a polished spoon, can also reflect light.
Thinking a bigger object always makes a bigger shadow. The size of the shadow also depends on how close the object is to the light source, not just how big the object is.

FAQs

Why does a mirror show my reflection but a wall does not?

A mirror has an extremely smooth and shiny surface that bounces light straight back to your eyes in an organized way. A wall is rough, so it scatters light in many directions and does not send a clear picture back to you.

Can light bounce more than once?

Yes! Light can keep bouncing off surfaces again and again. If you stand between two mirrors facing each other, you can see your reflection repeating many times because light bounces back and forth between them.

Why is my shadow sometimes long and sometimes short?

It depends on where the light source is. When the sun is low in the sky in the morning or evening, your shadow is long. When the sun is high in the sky at midday, your shadow is short and almost under your feet.

Does light bounce off water?

Yes! Water has a smooth surface and can reflect light. That is why you can see reflections of trees and clouds in a still pond or lake.

What happens to the light that gets blocked? Where does it go?

When an opaque object blocks light, the light energy is absorbed into the object, which can make the object feel slightly warmer. The light does not disappear; it just changes into a tiny bit of heat energy.

Is glass transparent or opaque?

Clear glass is transparent because light passes right through it. But painted glass or very thick glass can be opaque or translucent, blocking some or all light. It depends on the type of glass.

Want the whole picture for your child?

Every K–6 subject, an AI tutor that teaches step by step, unlimited practice, and a reward world.

Start a 3-day free trial