Light 4th Grade Science

Core Content Unifying Concepts SC-04-4.6.2 Students will: analyze data/evidence of the Sun providing light and heat to earth; use data/evidence to substantiate the conclusion that the Sun’s light and heat are necessary to sustaining life on Earth. Simple observations, experiments and data collection begin to reveal that the Sun provides the light and heat necessary to maintain the temperature of Earth. Evidence collected and analyzed should be used to substantiate the conclusion that the sun’s light and heat are necessary to sustain life on Earth.

Essential Questions How does light travel? What happens when light strikes an object?

Vocabulary Reflection – The bouncing of light off an object. Refraction – The bending of the path of light when it moves from one kind of matter to another. Absorption –The stopping of light when it hits a wall or other opaque object. Opaque – Reflecting or absorbing all light; no image can be seen. Translucent – Allowing some light to pass through; blurry image can be seen. Transparent – Allows most light to pass through; clear image can be seen.

Light Energy Did you know that energy is the ability to cause things to change. Ex. The energy in a fire changes a sheet of paper into ashes. The heat from a fire can change your hands from cold to warm. Light is also a kind of energy.

Light Energy cont’d. Without light energy, you could not see anything. Light gives things colors. Light energy can make many changes. The sun shines on the soil, and plants grow Doctors use light energy to perform operations Light energy can make cars move. In space, satellites and the space station use solar cells to change light energy into electricity.

Shadows Shadows occur when an object blocks light. When you put your hand in front of a lamp, you make a shadow on the wall because your hand has blocked the light. The shadows move and change shape when you move your hand.

Shadows Cont’d Light travels in straight lines. When you put your hand in front of a lamp, some of the straight lines of light hit your hand. The shadow on the wall shows where the light is blocked by your hand. When you move your hand, the shadow moves because your hand blocks different lines of light.

Shadows Cont’d When you stand in the sun, you block some of the lines of sunlight. As the sun moves in the sky, you block different lines of light. In the morning and afternoon, your shadow is long. When the sun is high overhead, your shadow is short.

Shadows Cont’d Long ago, people figured out that they could predict the pattern of changing shadows during the day. They used the pattern to tell time. A device used to do so is called a sun dial. As the sun moves across the sky, the shadow of the sun dial moves from left to right and points to the hours of the day.

Reflection Reflection is the bouncing of light off an object. Light bounces from a mirror like a ball bounces from a wall. If you roll a ball straight at a wall, it bounces straight back to you. If you roll a ball toward a wall at an angle. Light strikes a mirror at an angle and bounces to your eyes.

Reflection Cont’d Light bouncing off a smooth surface gives an image you can see. A mirror is very smooth. So are shiny metal and still water. You can see yourself in these things. But most things aren’t as smooth as mirrors. Most things are bumpy. When light hits a bumpy surface, each straight line of light goes off in a different direction, so you can’t see an image.

A mirror can also have a smooth, curved surface A mirror can also have a smooth, curved surface. Mirrors like this make your reflection seem bigger or smaller than you really are. Carnival fun houses and science museums often have such mirrors on display.

Refraction Refraction is the bending of light when it travels from one kind of matter to another. Refraction happens when light goes through a surface instead of reflecting.

Refraction Cont’d Refraction happens because light travels at different speeds in air, water, and glass. If light hits new matter straight on, it keeps going straight. But if light hits the new matter at a slant, the light bends or refracts. Ex. In line skater dropping off concerete onto grass

Refraction Cont’d Examples of refraction: Magnifying glass Glasses Contact lenses

Stopping Light Absorption – When light hits an object and is stopped or absorbed by the object. Ex. Rain falling on grass is absorbed like most matter absorbs light. When light hits most objects, some of the light bounces off and the rest is absorbed. Smooth, shiny objects reflect light. Other objects absorb most of the light that hits them and reflect the rest.

Stopping Light Cont’d Can you see your neighbor? No, you can only see the light that is being reflected off of him or her. You can’t actually see your neighbor. Think about it, can you see your neighbor if you turn off the lights? Nope. There is no light being reflected off him or her.

Stopping Light Cont’d There are three ways an object can interact with light. The light’s interaction with an object is based on what the object is made from. Opaque Translucent Transparent

Opaque An opaque object reflects or absorbs all light. If you try to look through an opaque object, you see only light reflecting from the object. Ex. Wooden door, ceiling, walls, floor

Translucent A translucent object reflects and absorbs some light. You can see a blurry or fuzzy image when you look through a translucent object. Some light is reflected from the object and goes through. Ex. Plastic cup, fogged window

Transparent A transparent object does not reflect or absorb much light. You can see a clear image when you look through a transparent object. Ex. Windows, plastic wrap, colored or clear glass

Ticket Out the Door How does light interact with a mirror? Your shadow is shorter than you at 10:00 in the morning. How do you predict its length will change over the next two hours? Give an example of an object that is opaque, translucent, and transparent. Tell whether each object reflects, absorbs, or reflects and absorbs light. You stick your hand in an aquarium to get something out. Why does your arm look as if it is broken?

Let’s Review Light energy can cause things to change. Plants require light to make food. Some machines use energy from light to generate electricity. Light travels in a straight line unless it is reflected, refracted, or absorbed. Mirrors produce clear images because their surfaces are smooth. Bumpy surfaces don’t produce clear images. Objects can be classified as opaque, transluscent, or transparent based on how they interact with light.