Orbits, Doppler, & Dark Matter Flashcards
What is Kepler’s first law?
Planetary orbits are elliptical in shape
What is Kepler’s second law?
The radius vector sweeps out equal areas in equal intervals of time
What is Kepler’s third law?
T^2 is proportional to r^3
time period squared is proportional to the radius cubed
How is Kepler’s third law derived?
› By equating the force an object in orbit feels due to gravity, and the centripetal force the object feels due to circular motion
› Circular motion equations for v and ω can then be subbed in
What is another name for the radius of an orbit when referring to planetary objects?
The semi-major axis
How is the existence of dark matter proven?
› When looking at spiral galaxies, stars which are distant from the central galactic bulge appear to move too fast
› The value for velocity is bigger than it should be, and as G is constant and r is fixed, M must be bigger
› In the equation v^2 = GM/r
› This ‘missing’ matter is referred to as dark matter
What is the Higgs boson and what does it cause?
› The Higgs field has a non-zero constant value almost anywhere
› As particles move through the Higgs field, they interact with it and accumulate mass (E=mc^2)
› The Higgs boson is incredibly unstable and decays almost immediately into a photon and dark matter
What are some examples of objects in mutual orbit? And what must they have to be in mutual orbit?
› Pluto and its moon Charon
› Binary star systems
› The two objects must have similar mass
What two equations are equated when deriving the critical density of the universe equation?
› Kinetic energy equation and gravitational potential energy equations equated
› Density equation used (where volume is volume of a sphere, and mass is found from the other two equations)
› Hubble constant equation used
