In post #200:
The energy of the collision is exacly the same in the 3 cases. Here the speeds are much lower than the speed of light, there is no need for relativistic mechanic, the speed simply add.
You would get the same result considering particules colliding at speeds near the speed of light. Here the speeds do not simply add.
The energy of the collision is exacly the same in the 3 cases. Here the speeds are much lower than the speed of light, there is no need for relativistic mechanic, the speed simply add.
You would get the same result considering particules colliding at speeds near the speed of light. Here the speeds do not simply add.
I'm not sure what is meant by 'energy of collision' so, in the interests of science, I am going to explore Kevin's figures! 
Momentum is always conserved in a collision, but in an inelastic collision kinetic energy is not.
The final velocity of the two vehicles equals the sum of their original momenta divided by the sum of their masses.
let's assume the vehicles have equal masses of 1 unit and use Kevin's speed figures.
Then, in the first scenario the lead car has a KE of 0 units and the following car has a KE of 0.5 units, a total KE of 0.5 units.
In the second scenario, the lead car has a KE of 50 units and the following car has a KE of 60.5 units, a total KE of 110.5 units.
The final velocity in the first scenario is 0.5 units, giving a the combined KE of 0.25 units.
The final velocity in scenario 2 is 10.5 units, giving a combined KE of 110.25 units.
However, the reduction in total KE is the same in each scenario (0.25 units) and this is the energy converted to other forms during the collision.
If my calculations are correct (and it's getting late!), I think this is in accord with Kevin's premise that the relative velocities are of little importance in classical physics - I wonder if he agrees?
Momentum is always conserved in a collision, but in an inelastic collision kinetic energy is not.
The final velocity of the two vehicles equals the sum of their original momenta divided by the sum of their masses.
let's assume the vehicles have equal masses of 1 unit and use Kevin's speed figures.
Then, in the first scenario the lead car has a KE of 0 units and the following car has a KE of 0.5 units, a total KE of 0.5 units.
In the second scenario, the lead car has a KE of 50 units and the following car has a KE of 60.5 units, a total KE of 110.5 units.
The final velocity in the first scenario is 0.5 units, giving a the combined KE of 0.25 units.
The final velocity in scenario 2 is 10.5 units, giving a combined KE of 110.25 units.
However, the reduction in total KE is the same in each scenario (0.25 units) and this is the energy converted to other forms during the collision.
If my calculations are correct (and it's getting late!), I think this is in accord with Kevin's premise that the relative velocities are of little importance in classical physics - I wonder if he agrees?
There is conservation of energy: kinetic energy m*v²/2 and collision energy ( heat, work to break and distord ).
And
There is conservation of momentum m*v
_1
momentum of the vehicules before collision = momentum of the wrecks.
_2
kinetic energy of the vehicules before collision = collision energy + kinetic energy of the wrecks.
And
There is conservation of momentum m*v
_1
momentum of the vehicules before collision = momentum of the wrecks.
_2
kinetic energy of the vehicules before collision = collision energy + kinetic energy of the wrecks.
Yes the point is that the energy difference in a 1m/s relative velocity can be very different depending on the actual velocity. In this terrestrial example the inertial frame of reference is the surface of the Earth. Energy is proportional to velocity squared so in the three examples when a car moving 1m/s faster than another car hits it the energy absorbed by closing the 1m/s difference is much larger when the velocity is higher. So to summarize in physics relative speeds are uninformative when it comes to understanding the kinematics.
Due to accelerating expansion of space, there is an approaching spherical event horizon at distance X from an observer where expansion rate equals C. To the observer, all matter existing at the sphere boundary would appear to have infinite mass, hence for all practical purpose appear as black hole. Does observation match that assumption? Is there any kind of event horizon effects like Hawking radiation?
Your calculations are correct.I'm not sure what is meant by 'energy of collision' so, in the interests of science, I am going to explore Kevin's figures!
Momentum is always conserved in a collision, but in an inelastic collision kinetic energy is not.
The final velocity of the two vehicles equals the sum of their original momenta divided by the sum of their masses.
5
let's assume the vehicles have equal masses of 1 unit and use Kevin's speed figures.
Then, in the first scenario the lead car has a KE of 0 units and the following car has a KE of 0.5 units, a total KE of 0.5 units.
In the second scenario, the lead car has a KE of 50 units and the following car has a KE of 60.5 units, a total KE of 110.5 units.
The final velocity in the first scenario is 0.5 units, giving a the combined KE of 0.25 units.
The final velocity in scenario 2 is 10.5 units, giving a combined KE of 110.25 units.
However, the reduction in total KE is the same in each scenario (0.25 units) and this is the energy converted to other forms during the collision.
If my calculations are correct (and it's getting late!), I think this is in accord with Kevin's premise that the relative velocities are of little importance in classical physics - I wonder if he agrees?
They are in the case of a non elastic collision where there is maximum damage, a maximum of kinetic energy converted into collision energy.
On the other hand, in the case of a perfectly elastic collision, the collision energy is 0, the vehicles swap their speeds.
Other collision cases exist, where the collision energy is something in between 0 and maximum.
Calculations are a bit more, but end up to the conclusion that the results only depend of the relative speed 1m / s regardless of the absolute speeds 0, 10, 100 m / s.
All theses calculations can be done again with unequal masses.
Then all theses can be done again with speeds where speeds are not negligible versus the speed of light. That is more involved because mass now depends of speed. If those calculations are done correctly using conservation of momentum and conservation of energy, the results will show it only depends of relative speeds.
It may be interesting to list the different hypotheses regarding the expansion of the universe.
1. The universe expands until the attractive force of gravity slows it down, and eventually causes it to collapse in on itself.
2. The universe continues to expand forever.
3. The rate of expansion slows towards zero, but never quite reaches it.
4. The rate of expansion of the universe is not slowing down but speeding up.
The most recent observations of the large-scale geometry of the universe have indicated the fourth model to be plausible.
So the question is, what force is responsible for pushing the universe apart ever faster against the attractive force of gravity?
Was Einstein right about the need for a for cosmological constant with its antigravity effects, or can we blame it on dark energy?
Or what about phantom energy? This is postulated to produce such a huge repulsive force that the universe will end in a Big Rip!
P.S. The Big Rip mechanism requires the acceleration of the universe to pass the speed of light, as mentioned by indra1. This does not defy special relativity since it involves the expansion of the universe itself, not particles moving within it. This would cause objects to leave our observable universe faster than its expansion, as light emitted from distant galaxies would not be able to "catch up" with the expansion. Indra1 likens this to a shrinking 'event horizon' for the entire universe.
About vehicle collisions studied in previous post, you have noticed that the collision energy is at best no more than half the kinetic energy of the
hitting vehicle.
This why at CERN they do not collide a proton beam to a fixed target.
They do collide two proton beams running opposite way for front head collisions.
With two 7 Tev proton beams they get 14 Tev collision energy. ( a single 7 Tev beam onto a fixed target would only get 3.5 Tev because when hit the fixed protons then move with a 3.5 Tev mass )
A 7 Tev proton beam is speeding at 99.9999991% the speed of light.
Yes, there are 8 nines.
This can be dug from internet and verified calculating from the mass at rest of the proton that is 938 Mev.
Using m = m0 / sqrt ( 1 - v² / c² ).
m = 7 Tev
m0 = 938 Mev
hitting vehicle.
This why at CERN they do not collide a proton beam to a fixed target.
They do collide two proton beams running opposite way for front head collisions.
With two 7 Tev proton beams they get 14 Tev collision energy. ( a single 7 Tev beam onto a fixed target would only get 3.5 Tev because when hit the fixed protons then move with a 3.5 Tev mass )
A 7 Tev proton beam is speeding at 99.9999991% the speed of light.
Yes, there are 8 nines.
This can be dug from internet and verified calculating from the mass at rest of the proton that is 938 Mev.
Using m = m0 / sqrt ( 1 - v² / c² ).
m = 7 Tev
m0 = 938 Mev
It may be worth explaining what an inertial reference frame is.
An inertial reference frame is one in which isolated objects will be either at rest or moving in a straight line at steady speed. If you sit in an inertial reference frame and place a ball on the floor it will be observed to remain at rest. Newton's first law of motion is therefore seen to apply in an inertial reference frame.
However, spinning reference frames are not inertial. For example, imagine sitting on a roundabout. Your frame of reference rotates with the roundabout. If you place a ball on the floor of the roundabout it will not be observed to remain at rest, but will accelerate outwards with no apparent force being applied to it. The laws of physics therefore appear to be different in this non-inertial reference frame.
There's no special inertial reference frame, but as long as we adhere to them the laws of nature will be the same in each.
We are approximately sitting in an inertial reference frame on the surface of the Earth and that is why we don't feel as if we are moving.
Last edited:
Member
Joined 2009
Paid Member
Yes we do not feel it is approximate. There is very little to become aware of it:
_Coriolis acceleration that explains some meteorological phenomenums at the tropics.
_Foucault pendulum experiment that shows earth rotation.
_Gravity that is a tad lower at the equator.
Where I come from, we call that "throwing gasoline on the bonfire".
Dark drink to nurish the discussion: At any rate, my very dark cherry wine is nearing a proper taste test, I'll take a picture later in the evening.
And in regards to beer, I really love porter, stout and bock type beers. But sometimes I want something a little bit lighter, in about 7 liters "light beer" consumption I will set a small batch of bock with a tiny bit of extra smoked malt mixed in.
silverprout said:
Code:
$ dict onanism
2 definitions found
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Onanism \O"nan*ism\, n. [Onan (--Gen. xxxviii. 9): cf. F.
onanisme.]
Self-pollution; masturbation.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
onanism
n 1: manual stimulation of the genital organs (of yourself or
another) for sexual pleasure [syn: {masturbation},
{onanism}]
2: a method of birth control in which coitus is initiated but
the penis is deliberately withdrawn before ejaculation [syn:
{coitus interruptus}, {withdrawal method}, {withdrawal},
{pulling out}, {onanism}]Where does masturbation enter into what I wrote?
Shame on you.
Last edited:
I suspect it was an attempt at humour, what you wrote:
"That would be narcissistic and delusional, something worthy of embarrassment, and I dare also write, psychiatric treatment."
Was exactly the way the church and quite possibly some doctors and psychiatrists depicted the act of masturbation 100+ years ago, it's more or less a direct quote from some texts I've seen referenced. Probably not your intention, but I do see the reference. I thought it was funny, but I am not laughing at anyone in particular, merely the reference.
Perhaps it would be more beneficial to reply to some of the other posts, if you do not like a specific individuals response then perhaps write it down to "personal differences". We are all individuals, everyone is different, and very many of us do not have English as our main language.
"That would be narcissistic and delusional, something worthy of embarrassment, and I dare also write, psychiatric treatment."
Was exactly the way the church and quite possibly some doctors and psychiatrists depicted the act of masturbation 100+ years ago, it's more or less a direct quote from some texts I've seen referenced. Probably not your intention, but I do see the reference. I thought it was funny, but I am not laughing at anyone in particular, merely the reference.
Perhaps it would be more beneficial to reply to some of the other posts, if you do not like a specific individuals response then perhaps write it down to "personal differences". We are all individuals, everyone is different, and very many of us do not have English as our main language.
The expansion of the universe isn't really due to galaxies moving through space away from each other, but rather due to the stretching of space itself.
Although it's impossible for matter to move through space in a local inertial reference frame faster than the speed of light, it is possible for the distances between faraway galaxies to increase faster than the speed of light, due to the rate at which the space between them is stretching.
A speed of light expansion of the universe wouldn't have any effect on the matter that makes up the galaxies. Its energy or mass does not become infinite in the sense that matter approaching the speed of light in an inertial reference frame does.
To liken the anti-gravity expansion of the universe to the gravitational collapse of matter to form a black hole may be regarded as a 'stretch' too far.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.