ODU(part 2) Flashcards
What is a projectile
A projectile is any object which freely accelerates due to gravity whilst moving forward at the same time.
What are the 2 main types of projectiles
horizontal and angled
What 2 componenets are projectiles made up of
projectiles are made up of horizontal and vertical components which act independently.
Describe the horizontal component of a projectile
Constant velocity, no acceleration
Describe the vertical component of a projectile
constant downwards acceleration due to gravity, where a = 9.8 ms^-2
What is the formula for the horizontal component of velocity in an angled projectile
uh = ucos0
uh = initial horizontal speed
0 = angle of projectile
u = initial speed of projectile
What is the formula for the vertical component of velocity in an angled projectile
Uv = usin0
uv = initial vertical velocity
0 = angle of projectile
u = initial speed of projectile
The moon is a …
natural satellite
The ISS is an…
artificial satellite
What does gravitiation force between two objects depend on
the two masses
distance between their centres
State newtons law of gravitation
F = Gm1m2/r^2
m1 and m2 are masses of the two objects in kg
r is the distance between the centres of the objects.
G is the universal constant of gravitation.
State the universal constant of gravitation
G = 6.67*10^-11 Nm^2kg^-2 (given on data sheet)
the gravitational force between an object and a planet is its []
weight
What is a frame of reference
How you describe the motion of an object depends on how you observe it
What is an inertial reference frame
Simply two places that are moving at constant speeds relative to one another.
What is an absolute reference frame
A unique, universal frame of reference from which everything could be defined or measured. Einstein proved no such reference frame exists.
What are einsteins 2 postulates (assumptions)
1) observers moving at constant speed relative to one another (inertial frames) will observe the same laws of physics.
2) the speed of light in a vacuum is the same for all observers regardless of their motion relative to the light source.
What is time dilation
Time dilation is the difference in a time interval as measured by a stationary observer and a moving observer.
State the dilated time formula
t’ = t/ (√(1-(v/c)^2))
where t is proper time
t’ is dilated time
v is the velocity of the object relative to a rest frame
c is the speed of light in a vacuum
Define proper time
Proper time is the time measured in the frame in which the clock is at rest relative to the event. The time will always be shorter in the rest frame.
Define dilated time
Dilated time is the time measured on a clock that is moving with a constant velocity relative to you. The time will be longer so the clock is seen to be running slow.
What is length contraction
Length contraction is a difference in the length of an object as measured (parallel to the direction of travel) by a stationary observer and a moving observer.
What is the formula for length contraction
l’ = l(√(1-(v/c)^2))
Define proper length
Length measured by the observer at rest with respect to the moving object
Define contracted length
Contracted length of the object as measured by another observer.
What is the lorentz factor
The lorentz factor is a way of taking into account the speed of a moving object.
State the lorentz factor
Y = 1/(√(1-(v/c)^2))
At what point relative to c are relativistic effect neglible at
Relativistic effects are neglegible when speed are below about 0.1c
At what speed relative to c does length contraction become significant
0.8c
Dilated time is measured by
an observer who is not in the frame of reference that the event is taking place.
Length contraction only occurs in
the direction parallel to the motion.
What is the doppler effect
The doppler effect is the change in observed frequency when a sound source is moving relative to a stationary observer
What happens when a sound source is moving towards a stationary observer
more waves reach you per second so the frequency of the sound is increased (wavelength is decreased)
What happens when a sound source is moving away from a stationary observer
Less waves reach you per second so the frequency of the sound is decreased (wavelength is increased)
State the doppler equation
fo = fs(v/(v+/-vs)
where v is the velocity of sound
fo is frequency heard by the observer
fs is the frequency emmited by the source
vs is of the moving source
State 2 applications of the doppler effect
Ultrasound in medicine
Radar speed guns
Define redshift
When a lightsource is moving away from you, the frequency decreases, so the spectrum shifts to longer wavelengths. This is called redshift.This is the doppler effect applied to light.
State the redshift formula
z = (λo - λr)/ λr
where z is redshift (no units)
λo is the observed wavelength in metres
λr is the rest wavelength in metres
z is positive for _______ and negative for _________
Redshift, Blueshift
State the formula for redshift provided that stars and galaxies are moving at non relativistic speeds
z = v/c
where:
z is redshift with no units
v is recessional velocity of the star in metres per second
c is the speed of light in metres per second
What were Hubbles two conclusions (Hubble Lemaitre’s law)
1) The bigger the magnitude of the shift the greater the speed the galaxy was moving away from the earth.
2) The further away a galaxy is the greater the speed it is travelling
State 2 things known about the expansion of the universe
The galaxies do not expand (they are gavitationally bound)
Space between the galaxies expands carrying the galaxies with it.
State the hubble lemaitre’s law formula
V = Hod
where:
Ho is hubbles constant with units per second
d is distance to the galaxy from earth in metres, m
v is the recessional velocity of the galaxy in metres per second
Plotting a graph of recessional velocity of galaxies against their distnace from earth gives a straight line of best fit through the origin, the gradient of this graph gives….
the value for hubbles constant.
State hubbles constant
2.3x10^-18 s^-1
Explain how the age of the universe can be found using hubbles law
Hubbles law suggests that galaxies further away from us are moving away faster than galaxies closer to us.
Therefore the universe is expanding
If we asusume the rate of expansion is fixed then most galaxies have been moving apart at a constant rate.
So time taken for them to reach their relative positions (ie age of the universe) must be t = d/v
Since Ho = v/d, then the age of the universe = 1/Ho = 4.35x10^17 s
What is dark matter and how do we know it exists
We can determine the mass of galaxies from their orbital speed, but the total masses measured are bigger than the mass accounted for by the observable stars in a galaxy.
The unaccounted mass is called dark matter.
Why is the universe still expanding despite the existence of dark matter, what is opposing the additional gravitational effects caused by the increase of matter
Dark energy
Define dark energy
Dark energy is a source of energy capable of producing a force which acts against the gravitational force of attraction, pushing matter apart.
Ordinary matter and energy make up what % of the universe
4%
Dark energy makes up what % of the universe
74%
Dark matter makes up what % of the universe
22%
A hot star will appear what colours
blue ish
A cooler star will appear what colour
reddish
How does peak wavelength relate with temperature
Peak wavelength is shorter for hotter objects than for cooler objects
How does radiation relate with temperature of objects
Hotter objects emmit more radiation per units surface area per unit time than cooler objects.
