The reason for people to swim easier in salt water than fresh water is because of buoyancy
Explanation:
In fresh water there is lack of minerals and has fresh water alone. The density of fresh water is 1000 kg/m³. Hence, in fresh water cannot exert the suitable buoyancy for the swimmer to float easier than that of salt water.
But in Salt water due to enrichment of salts and minerals it is found that salt water has more density than fresh water. Here the salt water offers more buoyancy to the swimmer to lift him up in the water surface and to swim faster and easier than fresh water.
It is similar to that egg floats in the salt water and sinks inside the fresh water because of its own body weight.
Good. You can do some very interesting experiments with that equipment.
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0 degrees Celsius aka the melting point of water.... If you look at the diagram I attached you notice that at 0 degrees Celsius it is flat, this is because much heat is needed at this point for water to rise to 1 degree... It is the same for the boiling point (100)<span />
Electromagnets have certain advantages over permanent magnets. One of the major advantage is, the amount of electric current can easily be controlled, in turn, magnetic field can be controlled. Out of all the options, option D would be the best answer.
In short, Your Answer would be option D) Electromagnets can easily be turned on and off.
Hope this helps!