Why is it easier to swim in sea than in a pond or river?

Since sea water contains alot of salt the density of the sea water is higher as to the river water . So it makes it easier to swim in sea water

firearm identification is the process of analyzing the bullets and cartridge cases left at a crime scene to determine if they came from a particular firearm. marks on the bullets and cartridges may be common to every firearm of that type. these are called class characteristics.