Light Travels in a
Straight Line
apter 5
Ch
왖 Beams of sunlight travel in straight lines.
Have you ever seen beams of sunlight streaming down
through the clouds? A light beam is made up of many
light rays. A thin line of light energy is called a light ray.
Light beams and light rays always travel in straight lines.
This explains why shadows form behind objects. Shadows
form when an object blocks a light beam.
NEL
왖 Why is there a shadow
here?
97
Observe How Light Travels
Skills Focus: observing, measuring, inferring
1. On four index cards, draw lines from corner to corner to make
an X. Make a hole at the centre of the X with a hole punch.
For a review on
measuring length, see
the Skills Handbook,
page 228.
2. Stand the index cards up on a table using small lumps of
modelling clay. Place the cards about 10 cm apart and try to
make sure the holes are in a straight line.
3. Put a flashlight 10 cm from the first card. Turn on the flashlight.
If needed, put the flashlight on a book to make sure the light
goes through the holes.
4. Ask your teacher to darken your classroom. Can you see the
light coming through the last hole? If not, adjust your cards.
What does the light beam look like? Spray a fine mist of water
along the light beam to make it show up better.
5. Move one card out of line. Can you still see the light shining
through the last card? Explain what you see to a partner.
98
NEL
Offer opinions about
what you have read. Do
you think sundials have
any advantages over
modern clocks?
Compare your opinion
with a partner.
Before clocks were invented,
people used shadows to tell the
time. Sundials are made of an arm
that casts a shadow on a base.
Times are labelled around the base.
As Earth spins, the Sun appears to
travel across the sky. The shadow
made by the arm of the sundial
moves as the position of the Sun
in the sky changes.
noon
afternoon
morning
arm
base
1. In what type of path does light travel?
2. Why do you see shadows?
3. Why are there no shadows on faces when we take a picture
using a camera flash?
NEL
99