i don't understand this dot point... plz help (1 Viewer)

[d00d]

hey i'm writing my notes to briefly cover each of the dot points. and this one doesn't make sense! or is it just me...

2. Many factors have to be taken into account to achieve a successful rocket launch, maintain a stable orbit and return to Earth.

* define the term orbit velocity and the quantitive and qualitive relationship between orbital velocity, the gravitational constant, mass of the central body, mass of the satellite and the radius of the orbit using Kepler's Law of Periods.


Now, nowhere in kepler's 3rd law can i see m (for mass of the satellite) or a v (for orbital velocity)..... wtf are they going on about?

if u've got notes for this dot point can u plz post it up or fill me in. ta

 

[sukiyaki]

are you tokin abt re-entry? escape velocity

i done a heaps of dots points
but i have no idea what exactly that is under 0_O

so you noe what exaclt teh sub topic is?

im a bit lost

 

[Minai]

umm...I think this dot point has changed, coz its not in our (2002) syllabus

and sukiyaki, its on the topic of Geostationary satellites/motion of satellites

 

[d00d]

yeah it's new syllabus...

topic is space, and sub-topic is motion of satellites orbitting earth.

plz someone help me with that dot-point

 

[Lazarus]

Maybe Kepler's Law of Periods is different to Kepler's 3rd Law?

 

[d00d]

i'm pretty sure its the same thing coz in one of the textbooks (jacaranda i think) there's a sub-heading saying Kepler's Third Law - The Law of Periods.

can anyone else help me out? this lil dot pt is giving me a hard time

 

[d00d]

no ones got it yet

cmons fellas, the dot point is:

* define the term orbit velocity and the quantitive and qualitive relationship between orbital velocity, the gravitational constant, mass of the central body, mass of the satellite and the radius of the orbit using Kepler's Law of Periods.

 

[kini mini]

Originally posted by d00d
no ones got it yet

cmons fellas, the dot point is:

* define the term orbit velocity and the quantitive and qualitive relationship between orbital velocity, the gravitational constant, mass of the central body, mass of the satellite and the radius of the orbit using Kepler's Law of Periods.

You realise that is a potential 8 mark monster, albeit unlikely as it is calculations based and we can't have those anymore, oh no

AFAIK Kepler's Law of Periods is the T^2 / R^3 = k a constant, for satellites of the same body. Surely this simply needs a plug n chug with the various formulae like F = G x mass1 x mass2 / R^2? Then throw in centripetal force F = mrw^2 and you're home...

Connecting all those bits is your job, it's good practice. You've been shown the path and now you have to walk it..

 

[marsesbars]

Kepler's Third Law = Law of Periods, and mathematically it's:

  3
 r      G M
 --  = --------  
  2            2
 T      4 (pi)

* define the term orbit velocity and the quantitive and qualitive relationship between orbital velocity, the gravitational constant, mass of the central body, mass of the satellite and the radius of the orbit using Kepler's Law of Periods.

Now, nowhere in kepler's 3rd law can i see m (for mass of the satellite) or a v (for orbital velocity)..... wtf are they going on about?

Everything that is in the dot point is in the formula, except for:

* mass of satellite - because the ratio of r cubed to t squared is INDEPENDENT of the mass of the satellite! When you derive the formula the mass of satellite cancels out (the proof is in most textbooks). So if you have a feather and a Porsche in orbit at the same radius around a planet, the ratio of r cubed to t squared is the same for both of them.

* orbital velocity - Get radius (r) and period (T) and remember that distance = speed x time. So to get orbital velocity (speed) divide distance by time. Distance = circumference of orbit = 2 (pi) r. Time = T, the period. So, orbital velocity is

v  =   2 (pi) r 
       --------
           T

 

[d00d]

thx for that it really helped.

but according to jacaranda textbook, the orbital velocity is calculated by

v = square root of ( GM / r)

where M = mass of planet
r = radius of orbit

 

[wogboy]

The Jacaranda book is just putting v in terms of G, r, and M (note that by M, the mass of the object in the CENTRE of the orbit is the one that counts, not the orbiting mass). You can derive that formula simply by simultaneously solving the two equations by marsesbars and eliminating T mathematically.

 

[MiuMiu]

shit.............you people are maniacs!

 

[sukiyaki]

Originally posted by YEAR11
shit.............you people are maniacs!

i too also for that!

 

[d00d]

ok thx for that wogboy.

do u think i would need any formulas that aren't in the syllabus? coz the two we've been discussing above arn't in the syllabus, prolly not in the formula sheet either...

 

[CLuver?]

The law of periods qualitatively is just Keplers sketches of elliptical orbits, how bodies cover a smaller area of the elipse in the same amount of time and thus must move faster. (planets around our sun)

 

[Saintly Devil]

Originally posted by d00d

* define the term orbit velocity and the quantitive and qualitive relationship between orbital velocity, the gravitational constant, mass of the central body, mass of the satellite and the radius of the orbit using Kepler's Law of Periods.

This dot point is broken up into two parts.

First, define the term orbital velocity.

Second, Define the quantitative and qualitative relationship between orbital velocity, the gravitational constant, mass of the central body, mass of the satellite and the radius of the orbit using Kepler's Law of Periods.

Now, nowhere in kepler's 3rd law can i see m (for mass of the satellite) or a v (for orbital velocity)..... wtf are they going on about?

The mere fact that the mass of the satellite is not present in both the equation for orbital velocity and kepler's law of periods implies its relationship. The relationship is, that there is no relationship. i.e. the mass of the satellite doesn't determine the orbital velocity (and obviously it can't determine the mass of the planet, G, etc.)

Also for the orbital velocity, kepler's third law is essentially a redo of orbital velocity, so if u look in jacaranda, the step before where the formula given is:

2(pi)r__________(G*m_E)^0.5
------ = --------------------------
T ___________r^0.5

(ignore the underscore's, i'm crap at formatting)

This is basically saying orbital velocity = orbital velocity with just two ways to say it. so i think this is pretty much defining the relationship between orbital velocity and every other thing listed.

i think this is what is happening, although not too sure. i had a bit of trouble with this dot point as well. can anyone clarify it?

 

[Saintly Devil]

and just another dot point which is causing me some confusion:

*discuss the role of the Michelson-Morley experiments in making determinations about competing theories

I don't really know what this is talking about.

anyone?

 

[marsesbars]

*discuss the role of the Michelson-Morley experiments in making determinations about competing theories

Hmm.. my take on it is "how did the result of the MM experiment show how correct the theories of the day were?"

I think the sentence 'making determinations about theories' means seeing how well the theories hold up to experimental evidence.

Hrm, but what were the 'competing theories'? The MM experiment's result showed the ether theory didn't hold up, and people tried changing it to explain this:
1 the ether moves parallel with the earth
2 the earth drags the ether with it
3 the MM experiment equipment was being distorted by motion through the ether

4 Einstein tried to scrap the ether theory totally, saying there is NO ETHER, because light travels at a constant velocity and doesn't need a medium

Don't know if what i wrote is right though, so