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asomaso
is there relation between the velocity and the weight and why the weight of car decrease by increasing the velocity , i see it when i pass beside a lorry very fast ?
yes of course ... ! But the weight increase I think ... ! When you drive faster , the velocity increases , It means that your Energy increases and by the formula \[E=mc ^{2}\] when the left side of equation increases , the right side must increase too. "c" is the speed of light (300000000 meter/second) and it's constant so we have increase in the mass. You can understand it by the fact that increasing speed is much harder in higher speeds than low speeds. For more info you can read Hawking's book, they are simple.("A brief history of time" & "The universe in a nutshell" I prefer the 2nd one.) ;-)
and the decrease that you mentioned is because of air molecules I think. Another parameter that is related to this action is p.(p=mv ,p=momentum, m=mass in kg , v=velocity in m/s). For sure you have experience it, when a huge lorry passes, you sense sth like a wind that this movement of the air is much powerful than when a car passes from in front of you. it depends on mass(Lorries have greater masses) and the velocity(actually speed, you can understand the difference in momentum in an example of 5 mile per hour and 50 mile per hour car) ... ! My English is not good , accept my excuse if I couldn't help you... ! ;-)
The weight of the car decreases because of an aerodynamic effect. Relativistic effects should be disconsidered except when dealing with objects near the speed of light or of an astronomically significant mass (such as a star).
as the velocity of the body increases air resistanse increases so the effect of weight decreases