Why doesn't the leaning tower of Pisa topple over?

Weightlessness in space: Space travellers as well as objects in the spacecraft appear to be floating. Why does this happen? Though the spacecradft is at a height from the surface of the earth the value of g there is not zero. In the space station the value of g is only 11% less than its value on the surface of the earth. Thus, the height of a spacecraft is not the reason for their weightlessness. Their weightlessness is caused by their being in the state of free fall. Though the spacecraft is not falling on the earth because of its velocity along the orbit, the only force acting on it is the gravitational force of the earth and therefore it is in a free fall state. As the velocity of free fall does not depend on the properties of an object, the velocity of free falls is the same for the spacecraft, the travellers and the objects in the craft. Thus, if a traveller releases an object from her hand, it will remain stationary with respect to her and will appear to be weightless. Why doesn't the spacecraft fall towards the Earth?

i. Will the velocity of a stone thrown vertically upwards remian constant or will it change with time? How will it change? ii. Why doesn't the stone move up all the time? Why does it fall down after reaching a certain height? iii. What does its maximum height depend on?

Why don't we hear sounds when our ears are closed?

The drift speed is defined as v_(d)=(Delta l//Delta t) where (Delta l)is the distance drifted in a long time (Delta t). Why don't we define the drift speed as the limit of (Delta l//Delta t) as (Delta t (rarr)0)?

If heavier bodies are attracted more strongly by the earth why don't they fal faster than the lighter bodies?

Which point effect in crystal doesn't alter the density of the relevant solid ?

Why crossing over does not take place in some species of male Drosphila?

Why don't we use water instead of mercury in Torricelli experiment? If we are ready to do this experiment, what length of tube is needed?