8.3 · Why Objects Look Colored

From Ohio 5th Grade Science Power Workbook · Chapter 8 · Lesson 8.3.

Big idea: An object looks a color because it reflects that color of light and absorbs the others.

Learning goals: Explain why an object looks the color it does

Explain why a black object looks black

Explain what happens to an object's color with no light

Reflected, not made

A red apple does not make red light. White light lands on it, the apple absorbs most of the colors in that light, and it reflects the red back.

The color you see is the color the object reflects. Everything else was absorbed.

Black, white and in between

A white object reflects nearly all the colors, which is why it stays cooler in sunlight.

A black object reflects almost nothing and absorbs nearly everything, which is why it looks black and why it warms up fastest.

No light, no color

Colors are not a property an object carries around by itself. They depend on light arriving and bouncing off.

In a room with no light at all, you cannot see a red apple or its color. The apple is still there, but no light reflected from it reaches your eyes.

Worked examples

Question: A student says a green leaf must be making green light, because it looks green even from far away. Explain what is really happening.

Steps: Ask whether the leaf glows in a dark room. It does not — with no light you cannot see it at all.

So the light must be coming from somewhere else and bouncing off.

White light lands on the leaf, the leaf absorbs most of the colors, and it reflects the green back to your eyes.

Answer: The leaf is not making light. White light lands on it, it absorbs most of the colors and reflects green, and that reflected green light is what reaches your eyes.

Common mistakes

A colored object does not make colored light

Because a red shirt looks red wherever you take it, it feels as though redness is something the shirt carries and gives off.

The shirt makes no light at all. It reflects the red part of whatever white light is landing on it, and absorbs the rest.

Check your thinking: Ask whether the object would glow in a completely dark room. If not, it is reflecting, not making.

Color depends on light

It is tempting to treat color as a fixed property, like how heavy something is.

Color only exists where light is arriving and bouncing off into your eyes. Take the light away and there is no color to see.

Check your thinking: If a question removes the light, remove the color from your answer too.

Remember

You see what bounces back

The color you see is the one the object did not absorb. Red apple — red bounced back, everything else soaked up.

Investigation

What happens to color when the light fades?

Question: Does an object look the same color when there is almost no light?

Safety: Do not make the room completely dark if anyone would have to walk across it. Leave a clear path and have an adult nearby.

Materials: three objects with strong colors: one red, one blue, one green

a room that can be darkened

a small flashlight

paper to record on

Steps: In bright light, write down what color each object looks.

Darken the room as much as you safely can and wait one minute.

Without switching anything on, say out loud (or remember) what color each object looks now. Write it down as soon as the lights are back on.

Shine the small flashlight on each object in turn and write down what color it looks under the flashlight.

Turn the lights back on, then repeat all the steps once more to check.

Compare your three sets of notes.

Fair: The objects never move and never change. The only thing different between the observations is how much light there is.

Cer: Prompt: What happened to how the colors looked as the light faded, and why?

Claim hint: Describe what happened to how the colors looked.

Ev hint: Give what you wrote down in bright light, in dim light and under the flashlight.

Re hint: Explain why color depends on light reaching the object and bouncing back to your eyes.

Practice tip

Remember: Name both halves.

Tip: Ohio's color questions want reflection and absorption. 'It reflects blue' is half an answer; 'and absorbs the other colors' is the other half, and usually the second point.

Written practice

Explain why a blue jacket looks blue in sunlight. Use the words reflect and absorb.

Sample response: Sunlight is white light, which contains all the colors. When it lands on the jacket, the jacket absorbs most of the colors and reflects the blue. That reflected blue light travels to my eyes, so the jacket looks blue.

Scoring guide: 1 point: says the jacket reflects blue light.

1 point: says it absorbs the other colors in the white light.

Ohio's content limit is the color of objects as it relates to reflection and absorption, so both words have to appear.