Sep. 27 – 2B03 27/09/2011 9:34:00 AM
Modern definition of the metre.
Vs. the historic piece of metal sitting in France.
Mass – piece of metal sitting in France.
4 fundamental forces of nature.
Strength of gravity:
Strong enough to kee moon in orbit around earth
Keeps galaxies together
o Balance between gravity of mass and motions of the stars.
Gravity acts on short as well as really long ranges.
Is it a strong force (relative to other forces?)
The Big Crunch idea -> possible scenario for outcome of the
universe (not the favoured model).
It is strong - the big crunch has gravity at its base.
Gravitational attraction between neighbour and I are small.
Force is too small.
Other fundamental forces:
1) Strong force – only imp. on incredibly small scales
o Keeping protons and neutrons in the nucleus -> keeps corks
o *We are using strong force as our metric.
2) Electromagnetic force –
o interaction of light w/ matter -> keeps atoms together
o 100x less strong than Strong force.
o Infinite range. 3) Weak force – main importance in nuclear decay (fission
o Only force imp. for neutrinos.
o Pretty weak
o Significantly weaker than Strong force.
IMP. forces for atoms & molecules.
4) Gravity – force of attraction of one amass on another