Which is normally greater: static friction or sliding friction on the same object?
static friction is normally greater than dynamic friction.
on the same object, static friction and dynamic friction are equal.
static friction and dynamic friction are both zero.
dynamic friction is normally greater than static friction.

Coefficient of static friction is normally greater than coefficient of sliding friction which is also known as coefficient of kinetic friction.

Explanation:

Coefficient of friction can be seen as the cumulative effect of the irregularities that are on the surface of objects. When these interlocking get locked into one another a resistance arises to the motion of the object which is termed as friction. When an object is static these irregularities get more time to be interlocked as compared to when an object is in motion thus the coefficient of static friction is more than the coefficient of sliding friction.

a.   mass number from atomic number

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia