Unit 1 - Our Dynamic Universe - Part 2

Question 1

why on earth do objects travel downwards with an acceleration of 9.8ms-2

Answer 1

gravitational field strength on earth

Question 2

in newtons universal law of gravitation what is G

Answer 2

gravitational constant (6.67x1011m3kg-1g-2) - in data booklet dont worry :)

Question 3

define a uniform field

Answer 3

constant in both strength and direction

Question 4

how do satellites stay in orbit?

Answer 4

the gravitational field keeps them accelerating towards earth and the earth’s surface falls away at the same rate

Question 5

what are some examples of natural satellites?

Answer 5

moon in orbiting earth and the planets in orbit around the Sun

Question 6

why does it not matter that charged particles and atoms experience a gravitational force?

Answer 6

it is insignificant as the electrical and nuclear forces are much stronger

Question 7

state Einstein’s postulates

Answer 7

The speed of light in a vacuum is a constant (3x10^8ms^-1) for all observers, regardless of their speed
The laws of physics are the same for all observers that travel at constant speed, within their own frame of reference

Question 8

what are the effects of special relativity?

Answer 8

Length contraction - disagreeing about the lengths of objects when they are moving relative to an observer
Time dilation - disagreeing on the passage of time when a clock is moving relative to an observer

Question 9

in the time dilation formula, what is the difference between t and t dash?

Answer 9

t is measured from perspective inside the frame of reference (astronaut on ship)
t dash is from observer outside the frame of reference (person on earth)
t dash = longer time
t= shorter time

Question 10

with length contraction what direction does the object contract?

Answer 10

the lengths of objects decreases in the direction of its motion from the point of view of the stationary observer

Question 11

in the length contraction formula, what is the difference between l and l dash?

Answer 11

l is measured from perspective inside the frame of reference (astronaut on ship)
l dash is from observer outside the frame of reference (person on earth)

Question 12

for a stationary source of noise what happens to wavelength and frequency?

Answer 12

same in all directions, waves form concentric circles

Question 13

if there is a source of noise moving towards you, what happens to wavelength and frequency?

Answer 13

the wave fronts are compressed, smaller wavelength higher frequency - therefore higher pitch sound

Question 14

if there is a source of noise moving away from you, what happens to wavelength and frequency?

Answer 14

the wave fronts are stretched, bigger wavelength lower frequency - therefore lower pitch sound

Question 15

what is fo?

Answer 15

frequency observed by the onlooker (Hz)

Question 16

what is fs?

Answer 16

frequency of the source (Hz)

Question 17

what is vs?

Answer 17

speed of the source (ms-1)

Question 18

for doppler effect equation when do you + and when do you use -?

Answer 18

+ when source is moving away, - when source is moving towards

Question 19

what happens to objects that move away from us

Answer 19

emit light - wave fronts more stretched out, larger wavelength and lower frequency. Light is therefore shifted towards the red end of the spectrum - redshift

Question 20

what happens to objects that move towards us

Answer 20

emit light - wave front less stretched out - smaller wavelength and larger frequency. Light shifted towards the blue part of the spectrum - blue shift

Question 21

define redshift

Answer 21

a measure of the ratio of the change of wavelength against the original wavelength or as the ratio of velocity of the receding object and the speed of light

Question 22

what did Hubble’s studies find out?

Answer 22

Hubble’s studies found that most galaxies are receding from us and the recessional velocity increases with distance. There was a near proportional relationship between these two: v ∝ d

Question 23

what is Ho in Hubble’s law?

Answer 23

Hubble’s constant 2.34x10-18s-1 in data booklet dont worry :)

Question 24

what is the estimated age of the universe?

Answer 24

13.8 billion years

Question 25

what is the four pieces of evidence that support the big bang?

Answer 25

Cosmic microwave background radiation Majority redshift if distant galaxies Abundance of hydrogen and helium Olbers' Paradox

Question 26

what is meant by abundance of hydrogen and helium?

Answer 26

the abundance of hydrogen and helium present in the universe today matches those predicted by the big bang model - heavier elements would not survive such an event and can only be produced later through fusion in stars and eventually in supernovae for the heaviest elements.

Question 27

what is meant by Olbers' Paradox?

Answer 27

if the universe was static and infinite in size and age then in every direction we look, we would eventually see the surface of a star and the sky would be constantly aglow. This is not true as stars move away from us and have not had enough time for their light to reach us yet. This tells us that the universe has a finite age (13.8 billion years) and is expanding.

Question 28

what is meant by Majority redshift if distant galaxies?

Answer 28

almost all galaxies are redshifted and therefore are moving away from us. In fact almost all other galaxies are moving away from each other telling us that the universe is expanding and this expansions origin is the Big Bang

Question 29

what is meant by Cosmic microwave background radiation?

Answer 29

shortly after the big bang as the universe cooled enough for electrons to recombine with hydrogen and helium atoms this recombination resulted in the release of light from all of these atoms, everywhere, all at once and in every direction. This light has been stretched out with the expansion of the Universe into the microwave part of the spectrum and can still be detected in every direction today.

Question 30

how can we estimate the mass of a galaxy?

Answer 30

by the orbital speed of stars within it - greater gravitational force causes larger accelerations

Question 31

what is dark matter?

Answer 31

the stars in most galaxies move faster than predicted, something must be adding to the gravitational force that we cannot detect

Question 32

what is dark energy?

Answer 32

All of our observations suggest that the expansion of the universe is accelerating. However if gravity is an attractive force this expansion should be slowing and will eventually cause the universe to collapse again. This expansion must there fore be driven by some unseen and undetectable force

Question 33

JUST LEARN THIS: | dont really understand, cant turn into questions :)

Answer 33

Temperature of Stellar objects is related to the distribution of emitted radiation over a wide range of wavelengths Hotter stars are bluer as there is more light at shorter wavelengths - high peak and larger area of graph Cooler stars are redder as there is more light at longer wavelengths - low peak and small area of graph