The Constant Speed of Free Falling Objects

[isyang94]

When an object free falls, its accerleration is constant, but does its speed change? If so is it practicing uniform or non uniform motion?

 

[Dale]

That depends what you mean by acceleration. In relativity there are two distinct concepts called acceleration. One is proper acceleration, which is the acceleration measured by an accelerometer. The other is coordinate acceleration, which is the second time derivative of the coordinate position.

An object in free-fall has a proper acceleration of 0, so its speed is constant in any local inertial frame.

In non-inertial frames it may have a non-zero coordinate acceleration so its speed would not be constant in that coordinate system.

 

[isyang94]

Acceleration as in the gravity 9.8m/s/s
thanks for the reply

 

[Passionflower]

When an object free falls, its accerleration is constant, but does its speed change? If so is it practicing uniform or non uniform motion?

Why do you mistakenly conclude that a free falling object's coordinate acceleration is always constant?

Consider a radially free falling test object approaching a black hole as modeled by the Schwarzschild solution, its coordinate acceleration is not constant and may in some cases and 'locations' even be negative (e.g. directed away from the black hole).