if a big stone and a small stone is dropped simultaneously from the certain height. they fall together why??

Because it takes more force to accelerate a mass, and gravity exerts more force on a greater mass.  So every object winds up with the same acceleration.  

And THAT, of course, says that all objects in the same gravity will pick up the same speed in the same time, and fall the same distance in the same time.

the simple machine has three main features. they are:

fulcrum is the center point or pivot point of the machine. effort is input force/ applied force. load is external force/ output.

the keisha 's machine labels are

x : load

y: fulcrum

z: lever