What causes the earth to increase gravitational acceleration in one direction and a derease in the opposite?

Question

Clarification= the changes of direction as it orbits the Sun at the aphelion and at the perehelion.

Answer 1

Conservation of energy. Because the force of gravity eminates from a single point - the Sun - you can't have a net change in energy. The energy can just be converted from potential energy to kinetic energy and back again.

For some given distance, there's a set amount of potential energy (GMm/r). It doesn't matter whether the object is moving towards the Sun, away from the Sun, or stationary.

There's also a set amount of gravitational force (GMm/r^2). Divide the force by the mass (the small m in the equation) and you get acceleration. Since the force and acceleration depend on r, then it's distance from the Sun is the only thing that matters. The object has the same acceleration towards the Sun regardless of the direction it's moving or if it's moving at all.

The AFFECT of acceleration does depend on how the object's moving. If the object is moving towards the Sun, it's speed increases. If it's moving away from Sun, it's speed decreases. Still, the magnitude in the change in speed is the same - only the sign changes. That means the increase and decrease in speed has to be symmetrical.

The kinetic energy depends on the speed (1/2 mv^2). As the Earth loses potential energy by moving closer to the Sun, the affects of being accelerated build up to increase kinetic energy at the same rate that potential energy is being lost.

Applying that to the motion, you had to start from somewhere. If you started with no speed, an object would still experience a gravitational force from the Sun and begin moving towards the Sun. As it's accelerated, it's speed increases. As it gets closer to the Sun, the acceleration increases, meaning the speed is increasing at an even faster rate. If you could pass through the center of the Sun, the decrease in speed would occur at exactly the same rate that the increase in speed occurred. In other words, you'd reach the same distance away from the Sun that you started, except on the opposite side of the Sun.

Since you're tossing in at least a little bit of lateral motion (tangential speed) to start with, the object never actually hits the Sun. That lateral motion puts the Earth on a trajectory that misses the Sun. But you still reach a point where the speed of the Earth has increased enough that the Sun's gravity can't keep pulling the Earth closer. That's virtually the same condition that would exist at the center of the Sun if the Earth just passed back and forth in a straight line. Instead of pulling the Earth closer, the Sun just slows the Earth down at the same rate that it sped up. The increase/decrease has to be perfectly symmetrical since the force acting on the Earth depends only on its distance from the Sun, not the direction it's travelling. That means the Sun can only remove the kinetic energy it supplied. The tangential motion you started with can't be removed.

Answer 2

It's the other way around, the magnetic field is generated by the spinning action of the Earth's molten iron core acting like a huge dynamo. There is measurable evidence that the Earth's magnetic field is in a state of flux (no pun intended!) and that there are several areas of N magnetic field currently appearing in the southern hemisphere and vice-versa. Now, I'm only guessing here, but it seems reasonable to assume that the only way the magnetic field could possibly change it's orientation would be if the Earth's core changed it's orientation as well. So, you might assume that if the magnetic poles flipped N to S, then the Earth's core would also have flipped N to S as well. Now the core would be spinning in the opposite direction to previously. At present, the Earth spins anti-clockwise, but if the core 'flipped' over then we would have the strange situation where the core would now be spinning clockwise while the outer crust and the mantle would still be spinning anti-clockwise. At this point one of two things would happen - either the core's momentum would prevail and the outer shell would slow to a stop and then start spinning the other way, in which case the Sun would now rise in the West and set in the East ! Conversely, the shell's momentum could prevail and the core would eventually slow to a stop and then start spinning the other way, in effect flipping the entire magnetic field over again. If either of these events would actually happen is purely conjectural, but, there is geological evidence that the magnetic field flips on a regular basis every 100,000 years or so. Apparently we're overdue for the next one, so we may get to find out sooner than we think! In any event, it's pretty safe to say that, whatever happens, there's going to be some pretty major earthquakes and upheavals around the world. Just as an aside, I remember reading a book on ancient history that made reference to some ancient text describing a cataclysmic event where the Earth flipped over and changed it's physical rotational direction. According to the text this happened within a matter of hours, at a time when the Sun rose in the West and set in the East every day. After the event it rose in the East and set in the West as it still does today. I'm pretty sure I've still got the book somewhere, I'll try and dig it out if I can, if I find it I'll post a link to it if you're interested.

Answer 3

Earth is not causing "acceleration" per se, but it's creating a gravitaitional field. Assuming the Earth is round (which it roughly is, but not quite), the strength of the gravitational field on the surface of the planet is uniform everywhere, and the force of gravity exerted onto objects will be directed to the Earth's center. When dropped, object will indeed undergo acceleration, same for all objects -- "g".

Answer 4

Gravity from the earth's mass attracts all objects that get near it. When things are moving towards the earth they accelerate faster and faster as the gravity gets higher the closer they are to the earth's surface. When something is going away from the earth, the object decelerates because the earth's gravity is trying to draw it back. For example, if you throw a ball into the air, it gradually decelerates slower and slower until it stops at its highest point. Then it starts accelerating faster and faster as it comes down and gets closer to the earth's surface.

Answer 5

Gravitational acceleration with respect to *what*?

The force due to gravity is a function of mass and the separation of mass between the objects of interest.

Answer 6

Your question doesn't make sense.