Syllabus Points (1 Viewer)

[allGenreGamer]

The half-yearly approaches... plz help me with some of the syllabus dot-points:

1. Explain that a changein gravitational potential energy is related to work done
2. Discuss the effect of the Earth's orbial motion and its rotational motion on the launch of a rocket
3. Account for the orbital decay of satellites in low Earth orbit
4. Identify that there's an optimum angle for safe-entry for a manned spacecraft into the earth's atmosphere and the consequences of failing to achieve this angle.
5. Discuss the importance of Newton's Law of Univseral Gravitation in understanding and calculating the motion of satellites
6. Discuss th role of the Michelson-Morley experiments in making determinations about competing theories
7. Identify that if c is constant then space and time become relative
8. Explain qualitatively and quantitatively the consequence of special relativity in relation to: the equivalence between mass and energy

Sorry i understand that there's a lot but it'd be a great review for all who enters this topic and especially to the one(s) who is(are) kind enough to discuss these dot points Thanks

 

[eneleon]

Originally posted by allGenreGamer
The half-yearly approaches... plz help me with some of the syllabus dot-points:

1. Explain that a changein gravitational potential energy is related to work donebetween mass and energy

Gravitational energy is energy that a mass has in relation to a gravitational field

PE=mgh

Gravitational potential energy is the work done to move a mass to a point which is also the same as the force required times the distance moved, which is again the same as m x g x h.

therefore you just hae to know the formula that gravitational potential energy is equal to mgh.

hope that helps you

 

[+:: $i[Q]u3 ::+]

sorry, i'll have to answer it in parts cuz i got a habit of writing uberlong answers then accidentally clearing the whole screen (i dont' quite understand hte new keyboard shortcuts on my new comp =P)

1. Explain that a changein gravitational potential energy is related to work done


An object with mass will have gravitational potential energy when placed in a gravitational field. Within this field, it experiences a force. To change this object's potential energy, it requires moving it to a different position in this field. work done = force x distance.

With an example: say if you have a ball. When you lift it, its gravitational potential energy increases because it's being moved away from the earth. But in order to lift it, you had to do work. On the other hand, if you drop it, its gpe decreases. This is because some of the potential energy has been converted into kinetic energy as the ball drops. The ball does work on the environment.

 

[+:: $i[Q]u3 ::+]

2. Discuss the effect of the Earth's orbial motion and its rotational motion on the launch of a rocket

the earth's rotational/orbital motion can be used to give a VELOCITY BOOST to the launch of a rocket.

When a satellite is fired into orbit, it is fired to the east to give it a velocity boost from the Earth's rotational motion. The velocity of the rocket relative to the launch pad is added to the velocity of the launch pad relative to the earth's rotational axis, to give an overall greater rocket launch velocity.

when a satellite is going to be fired into space, its launch is carefully timed so as to exploit the orbital velocity of the earth around the sun. The velocity of the satellite relative to the earth is added to the velocity of the earth relative to the sun (about which the earth orbits) to give an overall greater launch velocity.

This also means rockets can attain higher velocities whilst using less fuel.


3. Account for the orbital decay of satellites in low Earth orbit

all satellites in low earth orbit encounter a small degree of atmospheric drag. this comprises of air molecules that cause friction along the rocket. This eventually slows down the rocket, decaying their orbit. As the rocket slows, it spirals down towards earth, where there is denser air. More air molecules = more friction, and this speeds up the process. A lot of heat is generated (because of the friction) in this process and most satellites burn up before they reach the ground.

4. Identify that there's an optimum angle for safe-entry for a manned spacecraft into the earth's atmosphere and the consequences of failing to achieve this angle.

there is an optimum angle for safe reentry. -6.2 (+- 1) rel earth's horizon.
if the angle is too shallow, the rocket will bounce off the earth's atmosphere.
if the angle is too steep, the heat generated from hte friction and the high g-forces will be too much to ensure survival of the ship and its occupants.

 

[Xayma]

Originally posted by allGenreGamer
7. Identify that if c is constant then space and time become relative

Newtonian physics stated that space was relative and time wasn't.

For the special theory of relativity if c is to remain constant (ie have a constant speed) since speed=distance/time if one is relative then time must also change to keep a constant c.

 

[Constip8edSkunk]

5. Discuss the importance of Newton's Law of Univseral Gravitation in understanding and calculating the motion of satellites

It allows predictions and calculations of satellites orbital velocity and orbit
it can b equatede 2 centrpetal force
F=GMm/r^2=mv^2/r -> GM/r=v^2... giving the relationship btween orbital radius and velocity of teh satellite...facillitating the work required 4 launching satellites into desired orbits

6. Discuss th role of the Michelson-Morley experiments in making determinations about competing theories

The null result of the MM experiment showed the deficiency in the accepted aether model of the time. The null result contradicts the predicted results and this catalyzed a multitude of attempts to adjust the aether model(most notably by Lorentz) to suit the MM experiment and new theories/models to explain teh propagation of light. Einsteins special relativity became accepted partly due to the fact that it can be used to explain the MM experiment whereas the old aether model could not.

8. Explain qualitatively and quantitatively the consequence of special relativity in relation to: the equivalence between mass and energy

Mass and Energy are interchangeable. In Special Relativity, when travelling close to c, portions of kinetic energy is converted into mass by the eqn E=mc^2. This is termed mass dialation and the relativistic mass can be calculated by: m_v=m_o/sqrt[1-v^2/c^2]....note as v never reaches c, the mass increase(conversion of energy -> mass) is asymptotic, ie. v->c, m_v -> inf

 

[speersy]

i have also got a quick question.
In Space
explain lenght contration.
I don't know what to do as any explanation usually refers to time dilation (which the point after this one) or gives a massive einsteinyen thought experiment.

 

[+:: $i[Q]u3 ::+]

hmm...that einsteinian thought experiment is there for a reason =P have a read through it eh?
length contraction is based on a feature of special relativity; that the speed of light c is constant in all reference frames (regardless of how fast you are travelling) and this means length and time are not absolute. So the length of an object, or the time taken for an event to occur are actually dependent on how fast you are travelling. Basically, the length of an object, when observed from a frame in relative motion, 'contracts'.
e.g. if you are on earth, and you observe a spaceship going past at 0.6c, you are in relative motion to the spaceship. Because of this, length contraction occurs, and you see the ship shorter than it actually is. (ie if the craft is 10m long, then you might only see it as 5m long). But if you're on the spaceship, there's no relative motion between you and teh spaceship. So no length contraction occurs and the spacecraft you measure is still 10m long.

 

[t-i-m-m-y]

*looks at own notes

*looks at thread

goes back to uni work

 

[allGenreGamer]

More syllabus dot point questions:
1) Discuss importance of Newton's Law of Universal Gravitation in understanding/calculating motion of satellites.
2) Discuss the role of the Michelson-Morley experiments in making determinations about competing theories.
3) Competition between Westinghouse and Edison to supply electricity to cities (discuss)
4) Identify some of the energy transfers and transformations involving the conversion of electrical energy into more useful forms in home and industry.

Thanks eneleon, +:: $i[Q]u3 ::+, Xayma and Constip8edSkunk for helping with my previous questions. Thanks to you ppl I'm more confident with the coming exam.

*looks at own notes

*looks at thread

goes back to uni work

Yeah I know u r in uni and got 99% in HSC t-i-m-m-y, peace

 

[Xayma]

Did you also look at his notes? Because they probably cover it.

 

[Constip8edSkunk]

uh... yeah all the syllabus summaries and notes floating around here should cover these pretty well.. anyways, 1 and 2 are same as 5 and 6 in the 1st set.

3) Competition between Westinghouse and Edison to supply electricity to cities (discuss)
You can search the physics forum bout this... there are heaps of threads on this. basically edison's company used DC generator to generate electricity. due to energy loss through resistance in wires this was very inefficient. he had to build alot of power stations close 2 urban areas(to reduce transmission distance) which also wasnt very economically and environmentally viable. The problem with DC is that it is very difficult to be stepped up or down.

Tesla identified this problem but was frustralted that Edison ignored his advice while he was an employee there. So instead he went to Westinghouse and started up their AC electricity generation company. THrough Transformers, the electricity can b transmitted at very high voltages, reducing Power loss through heat from resistance in wires, allowing much more efficiency. Tesla also patented his design of a triple phase AC generator which effectively allowed the power 2 b generated in 3 phases out of phase with each other ...creating a much smoother form

Edison got pissed so he started a propaganda that AC is very VERY dangerous to handle while DC is safe. He performed public electricutions of horses cows and even an elephant using AC 2 prove his pt. At first the public were swayed by edison(as he was a somewhat famous figure); electricution using AC was even trialled for capital punishment(..it turned out pretty messy however so was abandoned).

But more and more ppl realised the much better model of AC transmission engineered by tesla and westinghouse, and they gained favour. This culminated at the world fair in sanfransisco(?) at the turn of the century where westinghouse won the rights 2 provide power 2 the festival, lighting up the fair with thousands of lightbulb at night, which won the adulation of the public. Also tesla himself demonstrated the safety of AC, dispelling much of the fear instilled by edison. since then AC transmission prospered while edison electric died out.

since its a 'discuss' you wanna focus on the for/against of each method of transmission(relate back to AC vs DC)... especially regarding the main issue, ie the versatillity and efficiency of transmission.

4) Identify some of the energy transfers and transformations involving the conversion of electrical energy into more useful forms in home and industry.


mechanical energy -> electrical energy at the generator... stepped up to over several hundered thousdand volts for transmission. this is then stepped down over a series of substaions as it approaches surburbia and finally at the pole transformer it is stepped down 2 240volts as it is supplied into the home, where it can be further stepped down in some appliances (eg. computers) while stepped up in others (eg. cathode ray tubes in tvs) then it is converted to sound, light, heat, etc depending on the appliance

 

[Dash]

Originally posted by t-i-m-m-y
*looks at own notes

*looks at thread

goes back to uni work

lol yeh...
looks like these questions have been thoroughly answered

 

[Constip8edSkunk]

The last few questions are not in the space topic