Pstti -Introduction of light
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Pstti -Introduction of light

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Pstti -Introduction of light Pstti -Introduction of light Presentation Transcript

  • PRASEEDA Student, PSTTI
  • DAY  A day is when there is light everywhere and the sun shines  We can see everything around us during day.  A day is from sunrise to sunset.
  • NIGHT  A night is when the sun does not shine and everything is dark  We can see the moon and stars in the sky.  Night is from the sunset to sunrise.  It is necessary to have the electric lights on at night.
  • Day time activities  We work and play  Flowers bloom  Birds fly  Animals are active
  • Night time activities  We sleep and rest at night  Some people work at night  Some animals hunt at night
  • The cycle of day and night  The day and night system helps us to live better on Earth.  When the sun comes up in the morning we get up and ready to go to school, work or play.  When it is night, we end up our activities and go to sleep.  We use this cycle of day as the way to identify when we should be active and when we should rest.
  • What causes day and night?  To answer the question let us do this      activity. Take a globe and a torch. Assume that the globe is the Earth and torch is the Sun. Now place the globe on the table and throw the light of the torch on it. Half of the globe will be lighted up. The other half will be dark.
  • Day and night  Now slowly rotate the globe  The half that was dark will be lighted .  The half that was lighted will be dark.  This shows that only that half of the globe that faces the torch gets light.  In the same way , when the Earth rotates from west to east, only half of it faces the sun.  This half which faces the sun has day .  The other half which does not get sunlight has night.
  • CONCLUTION  When the earth rotates, day changes to night and night changes to day.  Thus the rotation of the Earth causes day and night.  Earth makes one complete rotation every 24 hours.  A whole day lasts 24 hours and consists of both day(light) and night(dark).