What is the difference between the number of electrons in an atom of Iodine (I) and the number of electrons in an atom of Aluminum (Al)?

Asolid cylinder and a cylindrical shell have the same mass, same radius, and turn on frictionless, horizontal axles. the cylindrical shell has light-weight spokes connecting the shell to the axle. a rope is wrapped around each cylinder and tied to blocks of equal masses that are held the same height above the ground. both blocks are released simultaneously. the ropes do not slip. which block hits the ground first? or is it a tie?

What is friction? how does it affect the motion of an object?

Amagnetic field applies forces on: a)static chargesb)moving chargesc)water flow