# In physics problems, the earth is usually considered to be an inertial frame. The earth has a gravit

In physics problems, the earth is usually considered to be an inertial frame. The earth has a gravitational field and the second postulate of the general theory of relativity says:
"In the vicinity of any point, a gravitational field is equivalent to an accelerated frame of reference in gravity-free space (the principle of equivalence)."
Does this mean that accelerating frames of reference can be inertial?
You can still ask an expert for help

• Questions are typically answered in as fast as 30 minutes

Solve your problem for the price of one coffee

• Math expert for every subject
• Pay only if we can solve it

odvucimo1pp17
Accelerating frames are never truly inertial; however, in many situations the acceleration is sufficiently small that we can assume the accelerating frame to be inertial. It largely depends on the scale relevant to the problem.
For example, for purposes of projectile motion, we can consider the Earth to be an inertial reference frame and still model the projectile's path accurately. However, in orbital mechanics, we definitely cannot consider the Earth to be an inertial frame, since it constantly accelerates in its orbit around the Sun.
###### Not exactly what you’re looking for?
Noelle Wright
An inertial frame is equivalent to a frame's velocity at any given time. An accelerating frame still has intertial frames for the same reason that we can calculate instanteous slopes of a function. An accelerating frame is changing inertial frames constantly but that doesnt mean it isn't an inertial frame at a given point it time.