# Why there is no horizintal acceleration?

1. Dec 27, 2004

### Gughanath

When a stone is thrown over a clift, there is vertically acceleration, I don't understand why there is no horizintal acceleration?

2. Dec 27, 2004

### Clausius2

Hi London! How about my friend the BigBen?

Well, that depends on HOW do you throw the stone.If you merely leave it falling free it won't have any horizontal acceleration. But if you push it horizontally probably it will have horizontal acceleration.

3. Dec 27, 2004

### alpha_wolf

As soon as you let go of the stone, it will no longer have horizontal acceleration. This is due to Newton's 2nd law of motion, most videly known as F=ma. If there are no forces acting on the object, it will not accelerate. It's called inertia, and works independantly for each axis of any coordinate system.
EDIT: actually, inertia is Newton's first law, and the 2nd law (F=ma) is a generalization of the first.

Note however, that the above is an approximation: in real life, you usually have air, which causes a drag force propotional to the object's velocity. So in that case there is a horizontal acceleration (deceleration), but it is usually very small (because the horizontal velocity is usually small). You also have drag in the vertical direction, which is why you get a terminal velocity (= a velocity where the vertical drag balances out the object's weigth, so the object can't accelerate any further in the vertical direction).

Last edited: Dec 27, 2004
4. Dec 27, 2004

### Clausius2

Oops. Thanks alpha. Well, eeemmmmm.... I meant the deceleration due to air drag effects :tongue2: