What is the difference between masturbation and sex?

Let's try to figure it out: 1) During sex and during masturbation, a person is able to receive both physical and mental sexual stimulation. 2) Sex involves interaction with another person, therefore it requires more concentration and a greater level of arousal for successful intercourse. 3) Sex requires more effort from the body, therefore it affects it physically in a different way (the best cardio training).