Section 2: Light behaves in very predictable ways.๏ปฟ

Key Ideas     Unit Checklist

  Unit C: Section 2 โ€“ Introduction


Figure C.S.2.1 โ€“ ๏ปฟIn the early morning or late evening, objects block horizontal light rays to create long shadows.

Figure C.S.2.2 โ€“ Short shadows occur in the middle of sunny days.


Figure C.S.2.3 โ€“ Shadows form interesting shapes.
Shadows

Shadows are dark areas behind an object that demonstrate how light travels in straight lines. An object with a shadow absorbs and reflects light rays. The absorbed and reflected light rays cannot travel through the object to the other side. This creates a dark area with a similar outline to the object, which is the shadow.

The shape of shadows depends on the location of the light source. Outdoor shadows change through the course of a day because the sunโ€™s location changes position. At noon, the sun is at its highest point in the sky. Light rays travel down from the sun at a slight angle. The top view of an object blocks light, which is why shadows appear short in the middle of the day. Early or late in the day, the sunโ€™s light rays are nearly horizontal. The side of an object blocks more horizontal light rays, creating long shadows.

 Watch More

Shifting Shadows

๏ปฟWatch this video to learn more about how the length and direction of shadows change throughout the day .๏ปฟ

 
 

  Words to Think About:

Check out the word cloud below. It pictures the important words that you are going to learn in this section. Watch for these words, and combinations of these words, as you read. When you see them highlighted, you can click on them to learn more about what the word means. You can also visit the course glossary and read definitions for all of these words.


Lessons in This Section

Lesson C4: Reflection, Transmission, and Absorption
Key Question โ€“ How does light interact with other materials?

Lesson C5: Mathematics of Light
Key Question โ€“ What are some predictable patterns of light motion?

Lesson C6: Refraction and the Speed of Light
Key Question โ€“ Why does light change speed when it travels through different substances?

Lesson C7:  The Many Uses of Lenses
Key Question โ€“ How do lenses form images?

Lesson C8:  The Wave Model of Light
Key Question โ€“ What forms of electromagnetic radiation exist in addition to light? 
Reading and Materials for This Section

Science in Action 8
Reading: Pages 188โ€“225

Materials Lists for Unit:
Master List of all materials
Materials organized by lesson and activity

  Try It!


Shadows

Try this simple activity to observe how shadows form.

Download:

DOWNLOAD this document. It provides a space for you to record your observations later in this activity. Also use the document to write your answers to the analysis questions that you will find at the end of this activity.

Materials: 

  • Desk lamp
  • Wall
  • Meter stick or measuring tape
  • Pencil

Instructions: 
    1. Place the lamp at one end of a table.

    2. If possible, remove the lampshade from the desk lamp. Turn on the lamp.

    3. Hold the pencil upright below the lamp. The top of the pencil should be 10 cm below the top of the lamp.

       

       

    4. Measure and record the length of the pencilโ€™s shadow in the observations table.

    5. Have a friend or parent hold a meter stick or measuring tape that touches the top of the lamp and the top of the pencil. What do you observe about where the meter stick extends to touch the table?

    6. Repeat steps 3 to 5. Keep the pencil 10 cm below the light, but move it 20 cm to the side of the light to make your observations.




    7. Repeat steps 3 to 5 for the pencil at distances of 40, 60, 80, and 100 cm from the lamp.

Questions: 

Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.

The shadow became longer as you moved the pencil further away from the lamp. Rays of light coming from the lamp became more horizontal in relation to the pencil. This caused the side of the pencil to block more light rays, creating a longer shadow.
A line between the top of the lamp and the top of the pencil always extended in a straight line to touch the top of the shadow on the table, demonstrating that light travels in straight lines.