1- an example on a body that it is in motion to an observer and at rest to another. 2- examples of motions having the shapes of trajectory : rectilinear, circular and parabolic.

where is the circuit diagram ?

a.metals can become magnetic if they have many spinning electrons that create magnetic fields.d.only some metals are attracted by magnets; these metals are called ferromagnetic.

d.wrapping an insulated wire around a metal with ferromagnetic properties and applying an electric current.

3. dark matter

empty space could also be a simple vacuum