# B Objects randomly moving

1. Jan 23, 2017

### albertrichardf

Hello
This is a rather weird question but anyway...
Have you ever seen something just fall for no apparent reason? Its rather stable for some time and then suddenly it falls or moves? And you haven't touched anything. There is no wind. Nothing
What causes that?
It seems pretty strange, because there needs to be a force to make objects fall. I know there is gravity pulling it, but if it is balanced now, why would it not be balanced later?
Any idea what causes that?
Thanks

2. Jan 23, 2017

### rumborak

What one perceives as a stable, motionless object often is not. So, there are tiny imperceptible changes that occur that eventually result in the topple. This can be as "hidden" as a temperature change causing a slight expansion of the object, thus overcoming a former point of friction.

3. Jan 23, 2017

### albertrichardf

I see. Thanks for the explanation

4. Jan 23, 2017

### Staff: Mentor

@rumborak 's answer is a good one.

Think of a tree falling in the forest, or a sudden landslide on a mountain.

5. Jan 23, 2017

### albertrichardf

Real systems can't always maintain equilibrium because of the enormous number of variables to account for

6. Jan 23, 2017

### pixel

This happens sometimes in a dish rack if things are piled up. As the dishes dry over time, an item can move as the forces on it are no longer balanced in its initial position.

7. Jan 23, 2017

### Khashishi

In the case of a tree fruit, it is ripening over time, or drying or something, but the process is slow, so you view it as static, until it suddenly falls. On a microscopic scale, nothing is stationary. Take a look at https://en.wikipedia.org/wiki/Brownian_motion
At temperatures above absolute zero, you have molecules randomly moving around. These bump into larger objects and can cause the larger objects to move around a little bit. If the object is near a precipice, it could get knocked over by a small force.

8. Jan 23, 2017

### Staff: Mentor

So how many variables can real systems account for? Just kidding.

9. Jan 24, 2017

### albertrichardf

I was actually thinking of brownian motion as a cause for random movement. It's always interesting to see how the invisible will come to play into the visible when you least expect it.