module p7 l7
TRANSCRIPT
Module P7 L7
“If, in some cataclysm, all scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words?
“I believe it is the atomic hypothesis . . . that all things are made of atoms — little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another.
“In that one sentence you will see an enormous amount of information about the world, if just a little imagination and thinking are applied.”
Richard Feynman (1918-1988)
Nobel Laureate (1965) for the theory of Q.E.D. (Quantum
Electrodynamics)
Gas!The Kinetic Theory of Matter pictures matter as being made of particles in constant motion.
For example, a gas exerts pressure on the walls of the container because the particles are colliding with it.
Pump down the volumeIf the volume of a fixed mass of gas is reduced then the particles collide more often with the walls of the container so the pressure increases.
Pressure is inversely proportional to volume.
V
P
1/V
P
Change the temperature
If the temperature is increased then the particles move faster and collide with the walls more often.
Pressure increases with temperature.
t / °C
P
- 273
-273 °C is the temperature at which the pressure is zero i.e. the particles are not moving.
This is absolute zero - the coldest possible temperature.
t / °C
P
Note that the pressure is not proportional to the temperature in degrees Celsius.
(It’s a straight line with a +ve gradient but it doesn’t go through the origin.)
T / K
P
However, the pressure is proportional to the temperature in degrees Kelvin.
The zero of the Kelvin scale is at Absolute Zero.
°C K : Add 273
K °C : Subtract 273
Real exam question
Stars are not forever.
• This is the star Betelgeuse (“beetlejuice”) in the constellation of Orion.
• It is a Red Giant star.• It is in its ‘old age’.• Stars do not last forever.• They are ‘born’, ‘live’ and
‘die’
What does a ‘baby’ star look like?
• These huge clouds of gas and dust in deep space…
• …will eventually turn into a star (perhaps more than one).
The entire Solar System out to the orbit of Pluto could fit in here
A star is born: stage 1/5
• A huge cloud of dust and gas (larger than the Solar System)…
• …starts to shrink because of gravity.
• Gravity makes it fall in on itself.
[artist’s impression]
A star is born: stage 2/5
• The centre starts to get hot…
• …because of friction.• GPE is turning into
heat energy(GPE = gravitational potential energy)
[artist’s impression]
A star is born: stage 3/5
• The centre shrinks fast and becomes…
• …very hot and dense.
• It is called a protostar.
[artist’s impression]
A star is born: stage 4/5
• Nuclear fusion starts in the core.
• Hydrogen atoms are fused into helium atoms…
• …releasing huge amounts of energy.
• The star has begun to shine.
[artist’s impression]
A star is born: stage 5/5
• The light, heat and particles produced by the new star…
• …blow away the remains of the cloud.
• Some parts of the cloud may form planets.
[artist’s impression]
Young stars
• Stars often form in groups or clumps called clusters…
• This is a cluster of stars called the Pleiades.
• Note the left over gas cloud which gave birth to them.
• They are Blue Giants. They will ‘burn’ hotter and faster than our Sun. They will have shorter lives than the Sun even though they are larger.
A typical Main Sequence star
• Our Sun is about 4500 million years old.
• It ‘burns’ four million tons of fuel every second…
• …turning hydrogen into helium.
• It has got enough hydrogen to keep going as it is now…
• …for another 4500 million years!
• This stage is called the main sequence.
Death of the Sun: 1/3
• When the hydrogen fuel runs out…
• …the outside swells and the star becomes a Red Giant.
• When this happens to the Sun, the Earth will be swallowed up.
• The Sun will eat her children.
Death of the Sun: 2/3
• The outer layers of the star are blown away into space…
• …leaving a white dwarf which will eventually cool into a black dwarf.
Death of the Sun: 3/3
• From far away, this is what we would see.
• The white dwarf is the point of light in the centre of the circle.
[artist’s impression]
Death of a Big Star: 1/4
• A big star will become a Red Giant and then…
• …explode as a supernova.
• A supernova is the largest explosion in the Universe.
• For a few days, one star will outshine the 100 billion other stars in the galaxy.
[artist’s impression]
Death of a Big Star: 2/4
• The star literally blows itself to pieces.
• What is left behind is this…
• …shreds of gas and dust…
• …blown away from the star.
Death of a Big Star: 3/4
• If the star is 10 times the mass of the Sun…
• …it will become a neutron star.
• The pressure of the explosion and gravity squeezes the electrons into atoms until you get a solid ball of neutrons.
• The picture shows a jet shooting out of a neutron star in the constellation of Vela.
Death of a Big Star: 4/4
• An even bigger star may become a black hole.
• Here we see gas and dust spiralling into a black hole…
• …and getting hot as the particles collide with each other (which explains why black holes are not black)
You and the Universe…
The Sun is a second generation star.
The Sun and planets were formed from the ‘ashes’ of long dead stars.
Carbon atoms can only be formed inside stars. Organic molecules are based around carbon atoms.
This means that the theory of stellar evolution theory tells us that human beings are quite literally made from star-stuff.
Life Story of a Star – a summaryLife Story of a Human Life Story of a Star
BabyNEBULA: a giant cloud of dust and gas in space starts to collapse because of gravity.
ChildPROTOSTAR: the centre gets hot because GPE* is turned into heat energy. *GPE=gravitational potential energy
AdultMAIN SEQUENCE: nuclear fusion reactions (hydrogen into helium) start. The star is shining.
O.A.P.RED GIANT: the star runs out of hydrogen fuel and the outer layers swell and turn red as it fuses helium into heavier elements. The inner planets are destroyed as it grows.
DeathSmall star: outer layers blown away to leave a WHITE DWARF which eventually cools into a BLACK DWARF
Large star: explodes as a SUPERNOVA which leaves behind a NEUTRON STAR or BLACK HOLE.
Real Exam Question
