if gravity and acceleration are oppositely directed, is acceleration due to gravity valid?

Question

i'm basing it on the special theory of relativity.

Answer 1

That is, if an object is moving away at an increasing rate of speed from another object which exhibits a strong gravitational acceleration of its own?

Yes, acceleration due to gravity is still valid and must be considered in calculations.

See the bending of light around objects such as planets or black holes for an example.

Answer 2

"...If gravity and acceleration are oppositely directed..."

Not real sure how to interpret the above, but I'm guessing you're talking about an effect that goes something like this --

Imagine you mysteriously wake up in a closed box. You have no perception whatsoever of what's outside the box. You do feel gravity keeping you on the floor of the box. Later on you learn that the box was inside a spaceship accelerating at 9.8 meters/second/second. In other words, the effects of gravity and acceleration are identical.

From Einstein's General Theory of Relativity, not the Special Theory : )

Answer 3

According to Newton, objects at rest tend to remain at rest and those in motion tend to remain in motion unless acted upon by a force.

Thus, a force acting on an object can change its velocity.

Change in velocity is called acceleration.

Gravity is a force that causes acceleration. On Earth the rate of acceleration due to gravity is 32 feet per second per second... that is, gravity changes the velocity of an object 32 feet per second for every second the object is subjected to gravity.

The distance an object moves is determined by the following formula.

d = V₀ t + ½ a t² where V₀ is the initial velocity, a is the acceleration (caused by some force), and t is the time the object has been in motion.

The only time when gravity is acting against acceleration is when the object is moving upwards... or, in the case of orbiting objects, when it's just trying to stay up there.

Objects moving upwards are impelled by some kind of force (rockets or some other explosion, or even by hand--when you throw a rock upwards).

Objects remain in orbit because what is called centrifugal force. Centrifugal force is cause by the object's tendency to move in a straight line. The force that bends that trajectory is gravity. As long as the force exerted by gravity and that of centrifugal force balance, the object orbits.

Gravity is only "oppositely directed" when it interferes with an object's attempt to move upward. While gravity can't be "directed," it can be used. To pick up speed in space one might aim their craft at an object with a large gravity well. The force of gravity would increase the velocity in the direction of the object. The velocity of the craft would be great enough to shoot past the object. But, as soon as the craft was moving away from the object, all the benefits derived from flying towards the object would be lost because the gravity would be working against the object's direction of motion.

Answer 4

The special theory of relativity doesn't deal with gravity or accelerations.

Answer 5

Well, the special theory of relativity does have something to do with acceleration..or the lack thereof. Remember that this is based on an inertial frame of reference (no acceleration).

Answer 6

???
Where in SR does it say that gravity and acceleration are 'oppositely directed' ?

In any event, the total acceleration is just the vector sum of the individual accelerations.

Doug