Our Dynamic Universe Flashcards
Explain the equation Ft = mv - mu
Ft is the impulse
mv – mu is the change in momentum
What is the law of conservation of momentum
In the absence of external
forces the total momentum before a collision equals the total momentum after a collision.
m1u1 + m2u2 = m1v1 + m2v2
Recognise the formulae for work done, kinetic energy, gravitational potential energy and power
Ew = Fd
Ek =1⁄2mv2 Ep = mgh P = E/t
Describe why projectiles follow a curved path
They have a constant horizontal velocity (ignoring air resistance) and a constant vertical acceleration due to the force of gravity (weight)
How do you calculate the horizontal and vertical components of a vector?
Vh =Vcosθ
Vv =Vsinθ
How is the mass of a galaxy estimated?
By measuring the orbital speed of stars within the galaxy
What (simply put) is time Dilation?
Moving clocks appear to run slow (to an outside observer).
What is the Time Dilation formula in terms of the Lorentz Factor?
t’ = t γ
What is meant by the terms elastic and inelastic collisions ?
In an elastic collision both momentum and energy are conserved. In an inelastic collision only momentum is conserved
Write down the quantities and units for the equations
v = u + at
s = ut + 1/2at^2
v^2 =u^2 +2as
s is displacement (m) u is initial velocity (ms^-1) v is final velocity (ms^-1) a is acceleration (ms^-2) t is time (s)
State Newton’s First, Second and Third Laws of Motion
NI – If the forces on an object are balanced the objects velocity remains constant.
NII – If there is an unbalanced force then the object accelerates.
NIII – For every action force there is an equal size but opposite direction force.
What are three ways to find impulse?
Average force x time or Area under a force time graph or Change of momentum
Describe & explain the motion of a satellite.
Satellites are in free fall around a planet or star. They have a constant horizontal velocity and a constant vertical acceleration.
What do we mean by the phrase Conservation of Energy?
Energy is not created or destroyed it changes from one form to another
What do we get if we calculate the gradient or area of a velocity time graph?
Gradient calculates the acceleration. Area calculates the displacement.
What is Proper Time, t ?
The time measured in a f.rame in which the clock is at rest relative to the event e.g. the clock actually on the spaceship. Time is always shorter in this frame.
What (simply put) is Length Contraction?
Moving objects appear shortened (to an outside observer.)
What do measurements of galaxy velocities and their distance from us tell us about the universe?
The universe is expanding
How do you work out the component of weight acting down a slope?
Component of weight down slope
= mg sin θ
Give a second example showing Time Dilation
Clocks on satellites e.g. GPS, run slow. Systems must take this into account if they wish to calculate an accurate position.
What is Dilated Time, t’ ?
The time measured in a frame where you are observing the event from the outside e.g. on the planet watching the spaceship fly past. Time passes faster here. The moving clock seems to be running slow.
What is Proper Length, l ?
The length measured in a frame in which the measurer is at rest relative to the event e.g. the length actually measured on the spaceship. Length is always longer in this frame.
Formula for the Doppler Effect for sound
f0 = fs(V/V(+or-)Vs) V = Speed of sound Vs = Speed of source f0 = Observed frequency fs = Source frequency
Howdo you calculate a Z value? Give two methods
Z= Δ λ / λrest Z=v/c
What is Dilated Length, l’ ?
The length measured in a frame where you are observing the event from the outside e.g. on the planet watching the spaceship fly past. The moving object length is shorter.
Doppler Effect - if the source is approaching, do you add or subtract the source velocity in the divisor? Why?
Subtract the source velocity.
It makes the perceived frequency higher.
State the second basic postulate of special relativity
The speed of light in a vacuum is the same for all observers
What is Redshift?
A measure of the red- shift of an object, given as a fraction of the speed of light.
What is Blueshift?
Waves coming from a source moving towards an observer are measured to have a higher frequency (bluer) than the source
What is the Doppler Effect?
Observed change in frequency of a wave when the source is moving relative to the observer.
Newton’s law of gravitation.
F=Gm1m2/r^2.
F = force G = gravitational constant m_1 = mass of object 1 m_2 = mass of object 2 r = distance between centers of the masses
What is a Z value?
A measure of the red- shift of an object, given as a fraction of the speed of light.
Formula for Hubble’s Law
V = H0d V = Recessional velocity of a galaxy Ho = Hubble’s constant d = distance to the galaxy
Which Greek Letter represents the Lorentz Factor?
Gamma
γ
State the first basic postulate of Special Relativity.
Two observers moving at constant speed observe the SAME laws of Physics.
Give evidence for the existence of dark matter
Stars in galaxies are orbitting faster than predicted.
What is the Lorentz Factor?
1/√1-v ²/c ²
State the formula for Length Contraction
l’=l√1-v²/c²
State the formula for time dilation
t’= t /√1-vsquared/csquared
Give evidence to support the Big Bang Theory
Cosmic Microwave Background Radiation.
The abundance of hydrogen and helium.
The darkness of the sky (Olber’s Paradox).
Large number of galaxies showing redshift.
How is the age of the universe estimated from Hubble’s Law?
d/v = 1/Ho = age of universe
Give one example showing time dilation
Moving clocks appear to run slow to an outside observer
Describe the relationships between the temperature of a stellar object and the wavelength and irradiance of radiation emitted.
Peak wavelength is shorter for hotter objects. Hot objects emit more radiation per unit surface area per unit time.
Give evidence for the existence of dark energy
Cosmic microwave background radiation
The abundance of hydrogen and helium
The darkness of the sky(Olbers paradox)
Large number of galaxies showing redshift
