# Occurrence of Day/Night and Change in Seasons

#### Students’ Learning Outcomes

·         Define the term revolution.
·         Identify that the distance between the earth and The Sun, affects the time earth takes to revolve around the sun.
·         Explain that the Earth is tilted on its axis and this tilt causes seasons.

#### Information for Teachers

·         One round trip of an object around another is called a revolution. Time taken to complete one revolution is called time period.
·         The Earth revolves around the Sun.
·         Time taken by the Earth for one revolution is 365 days.
·         The path followed by the Earth is not exactly circular. It is an oval shaped path.
·         The Earth is tilted on its axis. That is why there is winter in the southern half of the Earth, when there is summer in the northern half.
·         The revolution of the Earth around the Sun and the tilt of axis of the Earth cause change in seasons.

#### Material / Resources

Torch, piece of chalk, a rubber ball, knitting needle, textbook

#### Worm up activity

·         Take a top and ask 2 or 3 students to spin it on the table or floor.
·         Ask the students to observe this movement closely and describe it.
·         Ask the students: What is a spin motion?
(Expected response: When an object rotates about its own axis, it is called spin motion. Axis is an imaginary line that passes through the center of an object)
·         Ask the students: Can something else spin?
(Expected response: Globe)
·         Ask them: Do you know that our Earth also spins like top?
·         After that introduce the today’s topic by asking various questions like:
v  Do you know what a revolution is?
v  What are the four seasons?
v  How do seasons change on the Earth?

#### Activity 1

·         Take a string of about half meter length.
·         Tie a small object at one end of the string.
·         Whirl the object around your head holding the other end of the string.
·         Ask the students: What is the shape of the path traced by the object? Is it circular?
·         Inform them that one complete round trip of an object around the other is called a revolution. Time taken to complete one revolution is called its time period.
·         The Earth also revolves around the Sun. this motion is called orbital motion.
·         The duration of one revolution of the Earth depends upon the distance of the Earth from the Sun.
·         If an object is at a distance larger than that of Earth from the Sun, its time period of revolution around the Sun will be larger.

#### Activity 2

·         Pass a knitting needle through a big rubber ball.
·         Mark a red line around the ball at the middle with a marker.
·         Draw an oval shaped line on the table.
·         Place a lighted bulb fitted in the holder at the center of the oval path.
·         Tilt the needle slightly towards right.
·         Ask the students to hold and observe the ball at position 1, 2. 3 and 4 turn by turn without changing the tilt.
·         Inform them that the distance of Earth from the Sun varies at these positions.
·         Ask them to observe the light of falling on ball. Then ask the following questions:
v  What will be the season on the part of the earth where the sun rays fall at right angle?
v  What will be the season on the part of the Earth where the sun rays don’t fall at right angle?
v  Show the students charts which mention the revolution of the Earth and four seasons.

#### Sum up / Conclusion

·         One round trip of an object about another is called a revolution.
·         The time period of a revolving object around the other object depends upon the distance between them. Greater the distance the longer is the time period.
·         The Earth makes one revolution around the Sun in 24 hours.
·         There is summer in the half portion of Earth on which sun rays are falling normally.
·         There is winter in the other half portion of Earth on which sun rays are not falling normally.
·         The season is moderate on both part of the Earth when the rays fall slightly oblique on both the halves.
·         The revolution of Earth and the tilt of its axis cause change in seasons.

#### Assessment

·         Ask oral questions to the students.
v  How the seasons on Earth are changed?
v  What do you know about the axis of the Earth?