2. Gravitational fields And Orbits Flashcards
Difference between EF and GF
Charge moves from positive to negative
GF the mass is only a positive value
Similarities between EF and GF
The relationship between their fieldstrengths and distance is an inverse square relationship
Fieldstrength becomes 0 at infinite away from a point
Gravitational force is proportional to …
mass
Weight =
mass x gravitational field strength
Gravitational field strength
force / mass
How could you show the earths gravitational field strength close to earth?
Using a pendulum with the same mass, use time and mass to calculate g in a period
Force between two masses equation
F = GM1M2 / r^2
What is the G constant
6.67 x 10^-11
what does r represent in the force mass equation
the distance between the centres of the two masses
Gravitational potential
the work done in bringing unit mass from infinity to that point
grativitational potential equation
Vg = -GM / r
gravitational energy equation
energy = m x g x change in h
work done equation
w = egrav= m x change in potential energy
on a graph how can you find the potential difference`
the area under the g -r graph
What other laws can be used to explain keplers laws
Newtons laws of gravtitation
What are keplers three laws
- The orbit is an elliptical shape with the sun at one focus
- A line joining the planet and the sun sweeps around in equal intervals of time and area
- The square of time period is proportional to the cube distance from the sun
What is the equation linking centripetal motion and orbits
GMm/r² = mv²/r
What is the doppler effect
If the object is moving towards the observer then the frequency appears to increase so is blueshifted.
If the object is moving away then the frequency decreases so is redshifted
Doppler effect equation
Changing in wavelength / wavelength = velocity of object / speed of light
The difference between observed wavelength and wavelength
Observed is the bottom of the equation which is the one seen from the galaxy
Wavelength is the normal length found in the lab on earth
So change in wavelength is the difference between the two values
Equation for time period of an orbit
T = 2Pi x square root of d³/ G ( m1 + m2)
What is the relationship between m1 and m2
The value of m1 is astronomically bigger than m2 so if need be we can assume that the mass of m2 is insignificant to the equation
This is the same as keplers third law
Radius of planet equation
r1 = (m2 / m1 + m2) x d
What is hubbles law
V = H⁰ x d
The recessional velocity is equal to hubbles constant time distance between earth and the galaxy
It also explains the relationship that the speed of travel is proportional to the distance travelled
Eg. The further they are the faster they are moving
What is hubbles constant
2.3 x 10 ^-18 s^-1
How do you estimate the age of the universe
Use 1 / hubbles constant which equals time in seconds
V = d/t so can substitute into equation
Why would the calculated age of the universe be different to the actual age
The calculated value assumes a constant rate of expansion using hubbles constant which we know isn’t true
Equation for the critical density of the universe
Pc = (3H⁰)² / 8Pi x G
What is dark matter
A type of matter that cannot be observed using EM radiation however we know it exists
How do we know dark matter exists?
- Use a velocity distance graph to show the difference between observed and calculated values for a galaxy
- Show that v is proportional to 1 / Square root of radius ( should work for all sections of the galaxy)
- Explain that the difference on the graph shows there must be other mass present
- As this mass is not seen it is written as dark matter
- If we didn’t have dark matter then the galaxies wouldn’t be able to rotate at the speeds it does
What is it meant by the critical density of the universe
The average density of the universe needed to halt its expansion
How do you explain keplers third law with equations
Force on two objects (orbits) = Centripetal force
Rearrange to get time squared is proportional to radius cubed
What is baryonic mass
The mass made from baryons like protons and neutrons
What is the higgs boson
An elementary particle observed by scientists to suggest the presence of dark matter
