# Simple FBD problem: person, chair, earth

## Homework Statement

A person is sitting on a chair. Draw force diagrams for the person, the chair, and the earth.

## Homework Equations

Identify the third law pairs too, por favor.

## The Attempt at a Solution

attached GIF is my attempt. what forces do i draw on the earth

thanks for the help

#### Attachments

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## Answers and Replies

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ranger
Gold Member
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
Homework Helper
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).