Why does the stick in a moving frame shrink vertically?

[heman]

dear friends,
i have one problem regarding the inertial frames.it is said that freely falling elevator satisfies the above property.if there are two particles inside the elevator the distance betn. them will remain same as long as the distance is small.but when the distance betn. the paricles is large there will be tidal force from which we can detect the external gravitational fields.

so my query is regarding the origin of tidal forces and this concept is not getting down my throat.please help me understand this concept i will be highly thankful to you.

 

[heman]

based on relativity

dear friends ,

this is the second concept in which i found difficulty to understand.let's consider an lab and rocket frame in which the x-axis of both the frames coincide in the beiginning and rocket will be moving wrt x axis.now the problem is if they both contain one stick and rocket's stick is below the lab stick then we will have to conclude that the moving stick will shrink in the vertical direction.thus i want to know why this will shrink in the vertical direction.and this consistency can be removed when tip of both the sticks will coincide and the sticks are arranged in vertical direction in both the frames.

please explain the concept involved.