Why does a mug full of water feel lighter inside water?

• According to Archimedes’ principle, when a body is immersed fully or partially in a liquid, it experiences an upward force that is equal to the weight of the liquid displaced by it. 
• The upward force exerted by the liquid on the body is known as upthrust or buoyant force.
• When a mug full of water is placed into water, it also experiences an upthrust and it is equal to the weight of the fluid that the body displaces. 
• The net force experienced by the mug can be given as:
  ${\mathrm{F}}_{\mathrm{net}}={\mathrm{F}}_{\mathrm{weight}}-{\mathrm{F}}_{\mathrm{upthrust}}$ 

Therefore, we can say that a mug full of water feels lighter inside the water because of buoyant force.