Our Dynamic Universe Flashcards
What is Dark Energy
The unidentified source of energy causing the accelerating expansion of the universe
What is Dark Matter
Material existing in space that we cannot detect - explains orbital speeds
Why should the expansion of the universe be decelerating?
The force of gravity should slow expansion
Why does the fate of the universe depend on its mass?
If the mass is large enough there will be a Big Crunch
If the mass is small enough there will be a Big Rip
Or expansion could go on indefinitely
How does the orbital speed of the sun determine the mass of our galaxy
Orbital speed of the sun is directly proportional to the mass inside of the orbit
Orbital speed -> gravitational force keeping it in orbit-> mass of galaxy inside orbit
How does the actual orbital speed of stars give evidence for dark matter?
The actual orbital speed of stars is greater than predicted which gives evidence of material inside galaxies which we cannot detect - dark matter
What is a stellar object?
a naturally occurring physical structure or entity that exists in the observable universe
Stellar objects emit radiation over a ….. range of wavelengths
Wide
Each object emitting radiation has a ….. wavelength which depends on its …….. and can use this to measure the ……. of a stellar object
Peak
Temperature
Temperature
Is peak wavelength shorter in hotter or cooler objects
Hotter
Hotter objects emit less radiation per unit surface area at all wavelengths than cooler objects. True or False.
False
Hotter objects emit more radiation at all wavelengths than cooler objects
How does Cosmic Microwave Background (CMB) radiation provide evidence for the big bang?
CMB radiation has been detected coming uniformly from all directions in the Universe. This suggests that it was produced at a single point and time. The big bang.
What is Olber’s paradox?
The darkness of the night sky suggests the universe is non -static (expanding)
What is Nucleosynthesis?
The ratio of hydrogen and helium in the universe is as expected if it were created in the early stages of the universe after the big bang
How does the temperature of the universe give evidence for the big bang
The average temperature of the universe is only 2.7k. This suggests that it has cooled down as it expanded after the big bang
What is average velocity?
The displacement per unit time
What is instantaneous velocity?
The velocity over a small time interval.
What is acceleration?
The change in velocity per unit time
What is terminal velocity?
When the force is acting on an object, moving through liquid or gas are balanced
What is the law of momentum?
Total momentum before a collision equals total momentum after a collision, in the absence of net external forces
What is the difference between elastic and inelastic collisions?
An elastic collision is when kinetic energy is conserved. An inelastic collision is when kinetic energy is not conserved
What is impulse?
Change in momentum
What rule do we follow when calculating explosions?
Total momentum before equals total momentum after
Why does a projectile follow a curved path/ how does a satellite stay in orbit?
They have a constant horizontal velocity and a constant acceleration downwards
Is the speed of light in a vacuum the same for all observers?
Yes
What is length contraction?
Objects travelling at relativistic speeds appear shorter than they would do at rest
What is time dilation?
As the speed of an object increases, the time measured by a stationary observer increases
What is the Doppler effect?
The change in frequency/ wavelength observed when a source of sound or light waves is moving, relative to an observer
What is redshift?
Light from objects moving away from us is shifted to longer more red wavelengths
