Physics 1 Topic 1

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Changing ideas about the Solar System

Geocentric - Everything orbits the Earth.

Heliocentric - Everything orbits the Sun:

  • Introduced by Copernicus.
  • Most convincing evidence for this theory was Galileo's observations.

Galileo's observations:

  • Observing Jupiter and saw three stars aligned near the planet
  • The next evening, the stars moved in the 'wrong' direction.
  • Week later, 4th star appeared. they never moved away from Jupiter
  • He then realised they were moons orbiting Jupiter.
  • Not everything orbited the Earth, proving geocentric model wrong.

Current model still says everything orbits the Sun, but the orbits are elliptical (oval) rather than circular.

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Visible Light and the Universe.

Most scientists know things about the universe due to detecting waves from objects in space.

Stars give out visible light which is why we can see them despite their distance from us.

We can see the plants because they reflect sunlight.

Early astronomers made observations using the naked eye.

Telescopes magnify images.

Telescopes on Earth have some issues which space telescopes can overcome - but they're expensive.

Telescopes can be used to take photographs of the universe, allowing 'zoom in'.

This makes it easier to share observations with others.

Faint objects can be seen by allowing a long exposure time so you can collect more light.

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Waves

Waves transfer energy and information without transferring matter.

  • Wavelength - the distance from one peak to the next
  • Frequency - how man complete waves there are per second (measured in Hertz)
  • Amplitude - the height of the wave (midline to peak)
  • Speed - how fast the wave goes.

Transverse: THE VIBRATIONS ARE AT 90* IN THE DIRECTION OF TRAVEL OF THE WAVE.

  • Light and all EM waves.
  • S-Waves.
  • Waves of strings and springs.
  • Ripples on water.

Longitudinal: THE VIBRATIONS ARE ALONG THE SAME DIRECTION THE WAVE IS TRAVELLING.

  • Sound and ultrasound
  • P-Waves
  • A slinky spring when you push and pull the end.
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Reflection and Refraction

Reflection:

  • When a wave hits a boundary between one medium and another, some of the energy is reflected.
  • The angle of reflection is the same as the angle of incidence.
  • The light's reflected because of the change in density. (How ultrasound scans work)

Refraction:

  • When a wave crosses a boundary between two substances, from glass 2 air, it changes speed
  • When light shines of a glass window pane, some of the light is reflected but a lot is passed through & gets refracted.
  • As the light passes from the air into the glass, it slows down causing the light ray to bend towards the normal
  • Light reachs 'glass 2 air' boundary on other side of window it speeds up and bends away from normal because its passing into a less dense medium.
  • The light ray that emerges on other side of glass is now travelling in the same direction as it started.
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