Question

a bird flies over a bus. what is the correct relationship of forces acting between the bird and the bus?

Explanation:

Step1: Recall force - interaction concept

In the absence of physical contact between the bird and the bus, there is no direct mechanical force between them. However, if we consider the gravitational force, every two objects with mass attract each other. The gravitational force between the bird and the bus is given by Newton's law of universal gravitation $F = G\frac{m_1m_2}{r^2}$, where $m_1$ and $m_2$ are the masses of the bird and the bus respectively, $r$ is the distance between their centers - of - mass, and $G$ is the gravitational constant. This force acts along the line connecting their centers - of - mass, which is a vertical direction in this case (assuming the bus is on a flat surface).

Answer:

The third option (the one with vertical up - and - down arrows)