Question

If the force of attraction btw earth and us is equal n opposite then why is the net force zero and if it is zero why do we get pulled towards earth

Answer 1

Answer:

Explanation:

It's not equal and opposite. You're thinking of Newton's 3rd Law. This is not that. This is gravitational attraction between 2 objects. We can figure out mathematically the pull that the earth has on a single person, by using the equation for gravitational force and the universal gravitational constant, G:

$F_g=\frac{Gm_1m_2}{r^2}$ where G is the universal gravitational constant, m1 is the mass of one person, m2 is the mass of the earth, and r-squared is the addition of the radius of the earth plus the radius of you in relation to the surface of the earth.

Let's say a person weighs 150 pounds; in Newtons this is 667 N (rounded from 667.233); his mass then, in terms of the metric system (using 9.8 for gravity), is 68.2 kg. Let's also say that this person is 6 feet tall. 6 feet is the same as 1.83 m (rounded to 3 sig fig's) and the radius from that person's center to the surface of the earth would be about half that height at r = .915 meters. Filling in the formula:

$F_g=\frac{(6.67*10^{-11})(68.2)(5.98*10^{24})}{(6.38*10^6)^2}$ it turns out that the person's radius adds nothing significantly to the radius of the earth, so it doesn't even count mathematically. It's way too small compared to the earth's radius (which is the denominator of that equation). We find that

$F_g=668N$ That's the pull that the earth has on that person which, not coincidentally, is the weight in pounds we said that the person was. Isn't physics amazing!?