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General Physics

Hot goIITian

 Joined: 25 Sep 2009 Post: 178
9 Apr 2010 16:25:20 IST
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12
823
its a challenge to all who say they are good in physics..
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its a challenge to all who say they are good in physics..

Hot goIITian

Joined: 25 Sep 2009
Posts: 178
9 Apr 2010 16:26:30 IST
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had there been negative masses existing on earth, the gravitational forces would have been---

1 attractive

2.repulsive

3.neither attractive nor repulsive

Blazing goIITian

Joined: 4 Aug 2009
Posts: 314
9 Apr 2010 16:44:51 IST
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i am not at all gud at physics, but still i would like to try....gravity is always an attractive force. if a negative mass is placed on earth's surface, it would move away from gravitational pull, and fall upward.but gravitational force has tendency to attract things towards itself. so a normal object will move towards earth, but in case of negative mass, earth will move towards object......so it is still a mystery, i guess!is it partly right???

Scorching goIITian

Joined: 19 Mar 2010
Posts: 247
9 Apr 2010 16:45:29 IST
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attractive, since F=Gm1m2/r2

(-m1)(-m2)=m1m2

therefore force is positive

Scorching goIITian

Joined: 19 Mar 2010
Posts: 247
9 Apr 2010 16:48:26 IST
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but if only one will be negative then the force will be repulsive

Blazing goIITian

Joined: 8 Oct 2008
Posts: 1252
9 Apr 2010 17:39:32 IST
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The answer is quite obious. And even a 8th class student can answer. But I guess thats not the answer right ?

New kid on the Block

Joined: 27 Mar 2010
Posts: 3
9 Apr 2010 18:16:05 IST
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Hot goIITian

Joined: 25 Sep 2009
Posts: 178
9 Apr 2010 18:38:41 IST
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well i must say none has been able to explain the correct answer right...speccialy..• » ÆσηιυΜ χєσηαχ «.

i m still in search for a perfect explanation..

Scorching goIITian

Joined: 26 Jul 2008
Posts: 290
9 Apr 2010 18:45:34 IST
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i think u wont get an answer,its not like charges or anything else.charges are given negative sign to simply distinguish the charges but mass can never be negative!!!just think what does really negative mass means? u cant because its obvious that it is meaningless

Scorching goIITian

Joined: 19 Mar 2010
Posts: 247
9 Apr 2010 18:49:05 IST
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#### Negative mass

Under general relativity, gravity is the result of following a spacial geometry (change in the normal shape of space) caused by local mass-energy. This theory holds that it is the altered shape of space, deformed by massive objects, that causes 'gravity', which is actually a property of deformed space rather than being a true force. Although the equations cannot produce a "negative geometry" normally, it is possible to do so using a "negative mass". The same equations do not, of themselves, rule out the existence of negative mass.

Both general relativity and Newtonian gravity appear to predict that negative mass would produce a repulsive gravitational field. In particular, Sir Hermann Bondi proposed in 1957 that negative gravitational mass, combined with negative inertial mass, would comply with the strong equivalence principle of general relativity theory and the Newtonian laws of conservation of linear momentum and energy. Bondi's proof yielded singularity free solutions for the relativity equations.In July 1988, Robert L. Forward presented a paper at the AIAA/ASME/SAE/ASEE 24TH Joint Propulsion Conference that proposed a Bondi negative gravitational mass propulsion system.Every point mass attracts every other point mass by a force pointing along the line intersecting both points. The force is proportional to the product of the two masses and inversely proportional to the square of the distance between the point masses:

$\mathbf{F_{12}} = G \frac{(-m_1) m_2}{r^2}\mathbf{r_{12}} = G \frac{m_1 m_2}{r^2}\mathbf{r_{21}} = \mathbf{-F_{21}},$

where:

• F12 is the magnitude of the gravitational force between the two point masses,
• G is the gravitational constant,
• m1 <0 is the (negative) mass of the first point mass,
• m2 >0 is the mass of the second point mass,
• r is the distance between the two point masses.

Bondi pointed out that a negative mass will fall toward (and not away from) "normal" matter, since although the gravitational force is repulsive, the negative mass (according to Newton's law, F=ma) responds by accelerating in the opposite of the direction of the force. Normal mass, on the other hand, will fall away from the negative matter. He noted that two identical masses, one positive and one negative, placed near each other will therefore self-accelerate in the direction of the line between them, with the negative mass chasing after the positive mass. Notice that because the negative mass acquires negative kinetic energy, the total energy of the accelerating masses remains at zero. Forward pointed out that the self-acceleration effect is due to the negative inertial mass, and could be seen induced without the gravititational forces between the particles.

The Standard Model of particle physics, which describes all presently known forms of matter, does not include negative mass. Although cosmological dark matter may consist of particles outside the Standard Model whose nature is unknown, their mass is ostensibly known - since they were postulated from their gravitational effects on surrounding objects, which implies their mass is positive. (The proposed cosmological dark energy, on the other hand, is more complicated, since according to general relativity the effects of both its energy density and its negative pressure contribute to its gravitational effect.)

Scorching goIITian

Joined: 19 Mar 2010
Posts: 247
9 Apr 2010 19:11:45 IST
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well explained or not??????????????

Hot goIITian

Joined: 25 Sep 2009
Posts: 178
9 Apr 2010 23:15:10 IST
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ya well explained...........

Blazing goIITian

Joined: 1 May 2009
Posts: 3960
10 Apr 2010 22:29:05 IST
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a negative mass implie an upward pinch in the space time fabric which will create a region on the fabric simiilar to a hilly proturbance on ground so it would make other nearby objescts roll away from it......................................................................

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