Which is a good example of a contact force?
a. protons in the nucleus of an atom
b. a ball falling down after it's thrown up into the air
c. a satellite orbiting earth
d. a bat hitting a ball

The right choice is (D) A bat hitting a ball

In physics, a contact force is a force that acts at the point of contact between two objects. In other word contact force is the force in which an object comes in contact with another object. On the other hand the non-contact force acts on the physically separated objects such as gravitational force or the force between the sun and stars or satellites. SO among the given options, a bat hitting the ball is the example of contact forces.

water at room temperature is flowing through a pipe with pressure taps located 10 ft apart along one section of the pipe, which are connected to a mercury (s=13.6) manometer.