Simple FBD problem: person, chair, earth

bobthebanana

1. The problem statement, all variables and given/known data
A person is sitting on a chair. Draw force diagrams for the person, the chair, and the earth.


2. Relevant equations
Identify the third law pairs too, por favor.


3. The attempt at a solution
attached GIF is my attempt. what forces do i draw on the earth

thanks for the help

Attached Thumbnails

 

bobthebanana

reply

ranger

In order for the chair to remain on the earth, the net force on the chair (with respect to the earth) must be zero. The weight of the total system is acting downwards on the earth and the earth is exerting a equal but opposite force.

andrevdh

The earth attracts the person and the chair (albeit separately!) and vice versa according to Newton's law of Universal gravitation. Since the chair presses into the earth (due to its attraction by the earth and the weight of the person sitting on it) it responds with a force of similar magnitude acting in the opposite direction on the chair (real forces always comes in pairs).