space

• the solar system


  sun, planets, and all the other objects that revolve around the sun
• planets


  major bodies that orbit a star that have a gravitational field strong enough to have pulled in any nearby objects (apart from their satellites)
• dwarf planets


  a celestial body resembling a small planet lacks the gravitational forces needed to pull in and accumulate all of the material found in their orbits
• moons


  smaller bodies that orbit planets and are natural satellites
• satellites


  any object that revolves around another object in space
• artificial satellites


  man-made objects that revolve around planets
• galaxy


  a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction
• gravity provides the force that creates...

  orbits
• planets move around the Sun in...

  (almost) circular orbits
• if an object is travelling in a circle it is constantly...

  changing direction, which means it it constantly accelerating (and changing velocity, but not speed)
• for an object is accelerate, there must be...

  a force acting on it - this force is directed towards the centre of the circle
• centripetal force


  a force that acts on a body moving in a circular path and is directed toward the center around which the body is moving
• why doesn't the object fall towards whatever its orbiting?

  because the object is already moving, so the centripetal force just causes it to change direction
• what keeps the object travelling in a circle while it accelerates?

  instantaneous velocity
• instantaneous velocity


  the velocity of an object at some instant or at a specific point in the object's path
• what is centripetal force provided by?

  the gravitational force between the planet and the Sun (or between the planet and its satellites)
• the size of the orbit depends on...

  the object's speed
• the closer you get to a star or planet, the stronger the ... is

  gravitational field
• the stronger the force, the ... the orbiting object needs to travel to remain in orbit

  faster
• for an object in a stable orbit, if the speed of the object changes...

  the radius of its orbit must do too
• faster moving objects will move in a stable orbit with a smaller radius than...


  slower moving ones
• what does centripetal force depend on?

  the mass of the object, its tangential velocity, and the distance of the object (radius) from the center of the circular path
• geostationary satellite


  a satellite that orbits the earth at the same rate that the earth rotates and thus remains over a fixed place above the equator. orbits take 24 hours, they are typically 36000km above the Earth's sea level and move at speeds of around 3km/s
• geostationary satellite uses


  communication, weather monitoring and navigation
• polar satellite


  a satellite that orbits Earth over its poles. orbits take around 100 minutes, they are typically 200km above the Earth's sea level and move at speeds of around 8km/s
• polar satellite uses


  military application, taking images of the Earth's surface and weather monitoring
• the universe seems to be...

  expanding
• galaxies in the universe seem to be moving...


  away from each other
• light from more distant galaxies have an ... wavelength


  increased
• red-shift


  the change in the wavelength of light due to an object moving away from the observer
• what do measurements of the red-shift indicate?

  The distant galaxies are moving away from us very quickly, and is the same result in whichever direction you look in
• more distant galaxies have ... red-shifts than nearer ones


  greater
• more distant galaxies are moving away ... than nearer ones

  faster
• Big Bang theory


  the theory that all the matter in the universe occupied a very small space (that was very dense and hot) and then it exploded, releasing all matter and energy and formed the universe - space started expanding from here, and the expansion is still going on at an increasing rate
• dark matter


  an unknown substance that holds galaxies together but does not give off electromagnetic radiation and is quite abundant in the universe
• dark energy


  a theoretical repulsive force that counteracts gravity and causes the universe to expand at an accelerating rate