mcpng

So you're saying that everything inside and the planet has a gravitational pull toward the centre. Within the planet, the net force is still toward the centre even though not as strong as the surface. And because it just so happens that there are tons of stuff stuck between the crust and the centre of gravity, the strongest gravitational forces at the crust pulling the crust inward squeezes everything in between. This gravitational force of the crust is stronger than the opposing force the rocks would give to protest being squeezed. Net effect, squeezed rocks, resulting ultimately in high temp. and core? If gravity is based solely on distance and mass, then the photon must have a mass, right? Let's say we give it the smallest possible mass, x. How does this work out using F = ma, and F = GMm/R^2 ? This may be straying off topic, but first thing I notice is...does a photon have acceleration? Considering the speed of light is constant in a vacuum, I supposed not. In that case, the force of light is 0 (which so far makes sense since i'm not being pushed away from my monitor). But, since gravity works on mass, GMm/R^2 is definitely >0. This means any gravitational pull should change the direction of the photon completely to head toward the centre of gravity. Since net gravitational force on earth is toward the ground, all light should just hit ground now. You wouldn't need a black hole.

Regarding the comments about nothing moving faster than the speed of light, isn't a black hole sucking things in faster than light? My terminology may not be right, but the idea being that "movement" is inward toward the centre of the black hole even for light. Otherwise, any reaction that sparks either on or inside the event horizon would have at least one beam of light moving in the exact opposite direction from the black hole's center, and this photon would effectively be static in space, absolutely no movement in or out the black hole? Plus, I know light is somewhat special, but considering the balloon analogy of the universe expanding, wouldn't a light particle be moving faster than the speed of light relative to something else in the opposite direction? If the stuff inside the crust has gravitational forces cancelling one another out, then shouldn't it just be free floating, net zero gravity? This still means that the crust should be the point of highest gravitational force. Like a doughnut being held together toward the center, even though the centre is hollow for example. The compression because there's stuff above it still requires some force to make sense of why anything above should exert pressure on anything below. If it's not gravity (and assumedly not the other 3 forces), then what is it?

Hi, New here, just needed to fire off some burning questions. Been watching some vids on cosmology and here are few things I really don't get and can't find internet data about: 1) Shouldn't gravitational pull be strongest at the surface of a planet (assume uniform density for sake of simplicity). The gravitational pull inside the planet should have some cancelling effects on one another, and in the core will be net zero. This is validated by some google searches. But then, why do we believe the planets have a core? Isn't it more sensible to think we're just a spherical shell, perhaps many kilometers thick, held toward a center of gravity? 2) Following up on question one, how does gravity explain the theory that massive objects exert a force so powerful in the center due to gravity, that it overcomes electromagnetic forces and begins the process of fusion? If fusion takes place, shouldn't it be where gravity is strongest, ie. at some radius away from the center of gravity? 3) If gravitational force is directly related to mass and indirectly to distance from the center of mass, then hypothetically, 2 tiniest particles in terms of size touching each other would have a gravitational pull of infinity (as r approaches 0). This is provided the r can approach 0 more than mass m can approach 0. However, if this were true, then these 2 tiniest particles can be hypothetically broken down to think about the smaller exact point of contact between the 2 particles. This makes the gravitational effect further approach infinity, upon which, an infinite gravitational field should not just be a black hole, but should instantaneously suck in the entire universe. Since this didn't happen, would it be accurate to say that hypothetically, in 2 tiniest particles, mass m approaches 0 faster than r approaches 0?