Both have to move
This fun activity helps us understand the relation between weight and friction. For this, you need a wooden stick.
Keep a finger each, beneath the ends of the stick. Try to slide one finger towards the centre. The other finger should stay where it is.
After moving a certain distance the finger stops and the sticks slide over the other finger. After a while, the stick stops and the first finger slides once again.
This continues until the fingers meet. The point where the fingers meet is the centre of gravity of the stick.
At this point you can balance the stick on one finger too.
If you slide an object on any surface, it encounters friction. The frictional force depends on roughness of the surfaces and the weight of the object. More the weight more is the friction.
Once again balance the stick keeping one finger near its centre and the other near its end. Feel that the stick exerts less weight on the finger, which is away from the centre.
In our experiment too, at any point of time, the finger farther from the centre is subjected to lesser weight, resulting in lesser friction and hence slides more easily.
Now, keep both the fingers below the centre of the stick and move them apart. Can you move both the fingers?