Question

3. You can experience the effect of the gravitational force of the earth on you, but you
cannot experience the effect of the gravitational force a bus standing near has on you.
Explain why

Answer 1

The gravitational force between any two objects(like bus and you) is explained through the equation of universal law of gravitation -

The Universal Gravitation Equation is: F = GMm/R2

where

F is the force of attraction between two objects in newtons (N)

G is the Universal Gravitational Constant = 6.674*10−11 N-m2/kg2

M and m are the masses of the two objects in kilograms (kg)

R is the separation in meters (m) between the objects, as measured from their centers of mass

here, the masses of bus and individual are so small compared to mass of earth, that force experienced between them is very small hence can not be felt. However it can be measured using very sensitive instruments.

to make it clear, see this example-

If a boy who weighed 74.8 kg) sat near a 50 kg girl, what would be the gravitational attraction between them, assuming the separation from their centers was 0.5 m?

Substituting the values into the equation: F = GMm/R2

where

M = 74.8 kg

m = 50 kg

R = 0.5 m

The result is:

F = (6.674*10−11 N-m2/kg2)(74.8 kg)(50 kg)/(0.5 m)2

F = 24961*10−11/0.25 N

F = 99843*10−11 N

F = 0.99843*10−6 N

This is approximately:

F = 10−6 N which is very small.