Physics Challenge Question 19 Solutions Part 1 W E

physics challenge question 19: solutions part 1 w e can find the gravitational attraction using the universal law of gravity. the e

Physics Challenge Question 19: Solutions
Part 1
W e can find the gravitational attraction using the universal
law of gravity.
The electrostatic attraction between the two is given by Coulomb’s
law.




Both are really small forces by everyday standards, but notice how
much bigger the electrostatic force is:

So, the electric force is 1039 times stronger; gravity seems
negligible in comparison!
Part 2
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All matter is made up of protons, electrons, and neutrons. Even though
the neutrons are neutral, the protons and electrons can interact
through the electrostatic force, which, as we just saw is stronger
than gravity. Yet, somehow, gravity determines how most matter moves
around the universe.
The reason is that, over length scales much larger than the atom’s
size (about 10-10 m), the charges in each atom cancel each other out!
(All atoms have the same number of protons and electrons, so from far
away, they “look” neutral.) Therefore, the small contribution from
gravity is all that remains.