GCSE Physics P8: Space

name the planets

mercury, venus, earth, mars, jupiter, saturn, uranus, neptune, pluto

larger plants have rings which means their gravitational force is stronger to attract debris

The Sun

• formed from a cloud of dust and gas (nebula) pulled together by gravitational attraction

• the sun is heliocentric (lies at the centre of our solar system)

solar system model

• initially earth was at the centre and everything else orbitted around earth

• geocentric model

• everything orbited in perfect circles

• with fixed background of stars

• then 600yrs later heliocentric model was formed

• its evidence was that mars had retrograde motion

• galileo observed moons orbiting jupiter showing not everything orbited earth

• kepler showed that planets orbited in ellipses not circles

planetry orbits

as planets orbit the sun, gravitational force causes the planet to change direction constantly (moves in a circle around the sun)

this means velocity is always changing hence the force causes the planet to accelerate without increasing its speed

relationships of orbits

for a stable orbit:

the radius must change if the speed changes

if the planet moves closer to the sun (orbital radius decreases) the gravitational attraction to the sun inreases (force increases, and so does acceleration)

so the orbital speed of the planet increases

life cycle of a star

• dust and gas cloud is present in a galaxy

• the gravitational attraction between the gas/dust particles draws them together

• the cloud becoes more concentrated, as the particles get closer

• the temp and pressure of the cloud increases as the particles get pushed so close together

• eventually the pressure gets so great that the dust/ gas particles are able to fuse together

• fusion occurs as light (mainly hydrogen gas) nuclei fuse together to form helium nucleu which creates a large amount of energy.

• this releases opposes the collapsing of the cloud due to gravity

• so eventually an equilibrium forms, where the energy is released due to fusion balances the pressure of gravitational collapse

• this means a star has now formed and it will stay like this for billions of years

• eventually the star runs out of gas to fuse which means that it is not in equilibrium so it collapses

• if massive the star will collapse increasing the pressure + temperature of the core, meaning heavier elements can fuse. once all the fusion has happened, it is too massive to be stable, so the star collapses, rebounds on its centre and produces a supernova what remains is either a neutron star or a black hole.

• if normal sized, the same process happens, less fusion occurs however (less fuel to fuse). the star collapses and produces a planetary nebula (a low scale supernova)

• a white dwarf remains

red shift

light appears red shifted from galaxies which are moving away from earth

the change with distance of each galaxy’s speed is evidence of an expanding universe so initially it must have been formed from a single point

• the distance from the galaxies expand

• light from a galaxy has its wavelength ‘red shifted’ as it sppears to move away from us

• as wavelength appears to get larger

• frequency decreases as each time a wavelength is emitted, the source (galaxy) is further away

planet

a collapsed star, with huge gravitational pull on nearby objects

moon

a natural object orbiting a planet 

natural satellite

celestial body formed by natural procesess

evidence for the big bang

• red shift

  shows the universe is exapanding so initially it must have been formed from a single point

• CMB

  cosmic microwave background radiation

CMB

when the universe was very young, the stars and rock would be very hot and emit lots of short - wavelength radiation

this radiation as a universe expanded over time and would have been stretched to become microwaves

this background radiation is present wherever you point a telescope in the sky which proves that the hot young universe has cooled and expanded since

there is still much about the universe that is not understood for example dark mass and dark energy