Space Physics (Part 1)

Space Physics (Part 1)

1. Circular motion

   • When an object moves in a circle at a constant speed, its direction of motion is changing all the time so it's velocity is also changing. Acceleration is the rate of change of velocity so the object must be accelerating. This means there must be a force acting on it. The force causing this circular motion is called centripetal force and acts towards the centre of the circle.
   • Swinging bung
     • The string provides the centripetal force to make the bung travel in a circle. The greater the mass of the bung the greater the force needed. The greater the speed of the bung the greater the force needed. If the string is released, the bung would travel in a straight line at a tangent to the circle.
   • The centripetal force needed to keep a planet in orbit is provided by gravity. The further a planet is from the sun, the weaker the gravity and the slower it travels. The planets follow an elliptical path (squashed circles) with the sun at one focus.

2. Satellites

   • Natural
     • Caused by collisions or explosions in space, an example of a natural satellite is our moon, Luna
   • Man made/ artificial
     • Made by humans and sent up to space to monitor space, an example of an artificial satellite is satnav
   • Satellites are objects that orbit a planet. Planets are not satellites, even though they orbit the sun.

3. Stars

   • Life history of a star
     • A cloud of dust and gas called a nebula will be drawn together by gravity forming a protostar. As it gets denser and hotter, nuclear fusioncan start and a star it born.
       • The star is stable as the force of gravity collapsing the star is balanced by the radiation pressure pushing out. When it runs out of hydrogen, a star the size of the sun will expand and cool to become a red giant. Some heavier elements will be fused in the core. Eventually it will shrink and heat becoming a white dwarf before cooling to become a black dwarf.
         • Much larger stars will expand to become a supergiant instead. They undergo a dramatic end, exploding in a supernove. The core is compressed becoming a neutron star or a black.
   • Life cycle of a star
     • Black hole
       • Supernova
         • Neutron star
         • Red Supergiant
           • Main sequence star (like the sun)
             • Red giant
               • STARS THE SAME MASS AS OUR SUN
               • White dwarf
                 • Black dwarf
             • Protostar
               • ALL STARS START AS A NEBULAR
           • STARS MUCH BIGGER THAN THE SUN
     • Stages of a star, after the Main Sequence period, to eventually become a Black Dwarf
       • The star will last for billions of years until all of the hydrogen has been fused. After that the core contracts briefly, fusing helium, then a build up of pressure causes massive expansion, so the star turns into a Red Giant.
         • When there is no more helium left, fusion stops and the star shrinks. This leaves a hot dead star, a White Dwarf.
           • This then cools, after time, leaving a Black Dwarf.
     • Stages of a star, much bigger than the sun, once the star has reached the end of the Main Sequence period.
       • Hydrogen fuss until there is no more left. After that the core contracts, temporarily fusing helium, then the star expands into a Red Super Giant.
         • Fusion continues with heavier substances until it reaches iron, then all fusion stops, the core collapses and the star becomes a Super Nova
           • All the heavier elements that were formed disperse into a new nebular. In a massive star the star becomes a Neutron Star
             • In a super massive star it becomes a Black Hole
   • Stars are formed when dust and gas from space are pulled together by gravitational attraction. Which starts getting hotter and fusing hidrogen
   • The rate of nuclear fusion in a large star is a lot faster than in a smaller star because the bigger star is hotter and so the particles collide faster
   • Scientist don't have good enough technology yet to calculate the exact mass of a star

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