|
|
|
|
|
|
|
|
|
|
Experimenting with rotation, revolution and Earth's tilt on its axis. |
|
FIRST
GRADE - EXPLORING NIGHT/DAY
OBJECTIVES:
VOCABULARY:
MATERIALS:
VIDEOS
BACKGROUND: The
Solar System and all its planets are in constant motion. Each of the
planets revolves around the Sun. The planets also rotate, or spin, around
an internal axis. One manifestation of rotation is the cycle of night and
day. Day after day, month after month, year after year, the alternation of
night and day continues. Sometimes it is sunny outside, and other times it
is dark. In addition to rotation, day and night occur because the Earth is
spherical. When a portion of the Earth faces the Sun, it is daytime. When
the same are rotates away from the Sun, it is nighttime. The cycle of
light and dark is continuous except near the North and South Pole. During
the Northern Hemisphere summer, the North Pole always faces the Sun, so
daytime is continuous for several weeks. At the same time, the South Pole
faces away from the Sun (Southern Hemisphere winter) and is in continuous
night. The
origin of night and day is very difficult for children to understand. The
idea that the dark side is really a shadow of the planet as it rotates
away from the Sun’s rays is difficult to imagine. The rotation of the
Earth on its axis, is also not easy to understand, because we cannot feel
this motion.
Light rays from the Sun touch only the side of the Earth that is facing
the Sun. While the Earth is spinning on its axis, it is also revolving
around the Sun. The Earth is always rotating, spinning eastward. We do not
sense this motion, however, because everything else on the Earth’s surface
is moving as well. There is no independent frame of reference for
observing rotation. Viewed from space, however, the Earth is clearly
spinning. A point on Earth takes 24 hours to complete one rotation and
come back to its starting point. The Earth spins completely once in 24
hours or in 1 day. The axis is the internal line around which the Earth
rotates. The axis is tilted 23.5o from an imaginary vertical
line drawn through the Earth.
Light rays from the Sun touch only the side of the Earth that is facing
the Sun. While the Earth is spinning on its axis, it is also revolving
around the Sun.
PROCEDURE:
1.
Last time we talked about what produced light in the sky (like … stars)
and what reflects light in the sky (like the moon and the planets, etc.).
Today we are going to put it together and talk about why we have
day and night, a year and seasons.
First you need to know two words “rotate” and “revolve”.
Rotate means to turn around on an
axis. Imagine there is a stick
going down my body and I turn around on it.
That is rotating (demonstrate).
Show them the globe rotating on its axis. Revolve means to go
around something. Use the
earth sun model to show the earth revolving around the sun.
You can also demonstrate by calling a student up and going around
them. So the earth is both
rotating and revolving around the sun at the same time.
2.
Play the rotation and revolution song.
3.
Have the students stand up, and rotate or spin. Make sure they understand
that this is rotation. 4.
Have students work in pairs. Have one student revolve around the other.
Explain that this is revolution.
5.
Tell the students that the Earth rotates as it revolves around the Sun.
Ask them to figure out what these motions will look like, using one pair
of students. Don’t let them do these activities for too long or else you
will have many dizzy students!
6. Explain why the Earth has night and day. Divide the students into groups
of two. Give each group a flashlight. Instruct them to think about
creating day and night. Have one student be the Sun by holding the
flashlight. The other student is the Earth (Earth Ball).
7.
Ask the students to create day in the United States, then night.
If one country is day, which country is in night?
Go through as many locations as it takes for the students to
understand the concept of day and night.
8. What causes day
and night? The shadow from one side of the Earth.
So the rotation of the earth is what causes …..(pause and let them
answer)… day and night since one side gets the light and the other is in
shadow. And the revolution of
the earth around the sun causes
….. (a year).
9. What causes the seasons???
Turns out it is the tilt of the earth on its axis!
10. Play video Bill Nye and
Seasons (this is just 4 minutes of a longer video but covers all important
parts)
11. Use the earth sun model in
the lab. When the northern
hemisphere is pointed toward the sun, it is summer there and winter in the
south. Then demonstrate the
reverse. Then show fall and
spring are in between. Tell
them you now get to act out the seasons using a flashlight and a Styrofoam
ball on a stick. Show them
that if the northern hemisphere is pointed toward the sun is it summer in
the northern hemisphere (and winter in the southern hemisphere).
When the northern hemisphere is pointed away it is winter in the
north and summer in the south.
Call out seasons and have them position their sun and earth balls
correctly.
12. Next, Stick a pushpin in
the middle or the northern hemisphere (~ where we are) on the Styrofoam
ball with the stick. Have one
person use a flashlight and face it directly at the ball.
Have them watch the shadows on the ball.
When is the shadow shorter? (summer, when the axis is pointed
toward the sun/flashlight).
When is the shadow longer (winter, when the axis is pointed away from the
sun/flashlight). How are the
length of the shadows during spring and fall? (in between length).
13. Tell them this is what is
happening in their measurements of the shadows in their long term project
they have been doing in class.
The shadows are longest in the winter when the northern hemisphere is
pointed away from the sun and shorter when the northern hemisphere is
pointed toward the sun. This
is why the days are longest in summer but the shadows are the shortest and
the days are shortest in winter but the shadows are the longest.
14. FINAL REVIEW (these can be
phrased as questions)
Rotation of the earth causes day and night
Revolution around the sun is our year.
Earth’s tilt is why we have seasons.
|
