Unit 1 - Kinematics And Dynamics Flashcards
Horizontal component velocity
U(h) = R*cosx°
Vertical component velocity
U(v) = R*sin°
Newton’s Universal Law of Gravitation
F = Gm(1)m(2)
————
r^2
G = gravitational constant (6.67*10^-11m^3kg^-1s^-2)
Gravitational field strength definition
The gravitational force per kilogram or weight per unit mass
Inverse square nature of gravitational force
As the distance between two masses increase, the gravitational force decreases
As it doubles, force quarters
As it triples, force is 1/9th etc
Why do satellites orbit?
Gravitational force exerted on satellite
Force accelerates the satellite
Orbital speed is constant, but velocity vector changes direction
Satellite follows curved path that follows the curvature of the Earth
Newton’s first law
Balanced forces mean the object will be at rest or constant velocity
Newton’s second law
Unbalanced forces accelerate masses
Newton’s third law
Each force exerts an equal and opposite reaction
If tension force and weight are balanced
At rest, constant upwards speed or constant speed downwards
If tension is greater than weight
Constant upward acceleration or constant downward acceleration
If weight is greater than tension
Constant downward acceleration
What must happen when calculating forces applied at an angle?
Get horizontal and vertical components
Equations for weight component
W(c) = WsinX°
Or
W(c) = mgsinX°
Equation for gravitational potential energy
E(p) = mgh
Equation for kinetic energy
E(k) = 1/2mv^2
Equation for work done
E(w) = Fd
What is momentum?
Product of mass and velocity:
p = mv
What is the principle of conservation of linear momentum
The total momentum before a collision or explosion is equal to the total momentum after a collision or explosion when there are no external forces like friction
What is an elastic collision
Total E(k) before = Total E(k) after
Total kinetic energy conserved
What is an inelastic collision?
More kinetic energy before collision
Most energy lost to heat
What happens in an explosion?
One mass splits into two Total E(k) increases Total energy and momentum conserved
Equations for impulse
Impulse = F(avg)*t(c)
Impulse = change in momentum
Impulse = mv-mu
F(avg)*t(c) = mv-mu
Impulse = area under graph
The effect of hardness of surface on impulse
Softer surfaces increase contact time which results in the average force being less if change in momentum is the same
Find random uncertainty
Random uncertainty = max-min --------- N
Calculate percentage uncertainty
Percentage uncertainty = Random Uncertainty --------------------- * 100 Mean
What uncertainty do you use when calculating something
Biggest uncertainty in one of the variable
Same with percentage
Analogue scales for uncertainties
Far apart divisions = 1/5
Close divisions = 1/2
Digital scale for uncertainties
Always +/-1 of the last digit
Eg 9.98 would be +/-0.01
Systematic uncertainties
Give consistently too high or too low reading
Eg scale that isn’t reading 0 before you weigh something
What happens during the Doppler effect
Sounds waves propagate outwards from the source at 340ms^-1 (in air)
Doppler effect when source is moving towards observer
Source is moving towards so waves bunch closer together and therefore the source is heard to be higher pitched
Doppler effect when source is moving away from observer
Source is moving away so waves spread further apart and therefore the source is heard to be lower pitched
What sign do we use when the source is moving away?
Away = add
What sign do we use when the source is moving towards the observer?
Towards = take away
Equation for Hubble’s constant
v = Hd
recession velocity = hubble’s constant * distance
Hubble’s constant = 2.3*10^-18s^-1
Redshift equations
z=v/c
Redshift = recession velocity / speed of light
z = observed wavelength - rest wavelength
————————————-
rest wavelength
How can the age of the universe be calculated?
Rewinding the expansion process back to a singularity at the start of the universe
t = 1 / Hubble’s constant
Evidence for the Big Bang
Expanding universe
Most galaxies redshifted
Rewinding expansion leads to singularity that contained everything in universe
Cosmic microwave background radiation- the “after glow” of the Big Bang
Abundance of hydrogen and helium as these were most likely to form as universe cooled from Big Bang
What is dark energy?
Fuels the expansion of the universe
What is dark matter?
Not detected easily as it weakly interacts with detectors
Evidence for dark matter?
Rotational speeds of galaxies requires a bigger gravitational force than can be accounted for by mass detected
Gravitational lensing - light is affected by dark matter which explains some astronomical explanations
How do you calculate temperature of stellar objects?
By plotting intensity of radiation against wavelength
Peak wavelength * temperature in kelvin = constant (2.9*10^-3)