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?
Development
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?
Follow up
· Suggest some low cost activities to develop the concept of change of seasons on Earth.
· Ask them to write two examples of revolution from daily life in their notebook.
