91Ó°ÊÓ

Given : A brick is falling from the roof of a three-story building.

If we have an object that is being acted upon by forces, we must be able to detect those forces. The technique for recognizing forces will be depicted in visual form, as seen in the picture below.

The following steps are taken to determine the forces:

1. We recognize the thing, which is a falling brick from the building.

2. As shown in the diagram, we draw a graphic for the brick.

3. We draw a closed circle or a curve around the object, as indicated in the figure below by the dashed curve.

4. We name and label the object's contact forces, which in this case is the drag force imposed by the air.

5. We name the long-range forces, which are merely gravity in this case.

As a result, we can determine the forces acting on the brick using the diagram, where the forces are the drag force$F_{drag}$due to air resistance, which acts in the upward direction of the brick's motion, and the gravitational force or the weight of the brick, which acts in the downward direction due to the brick's weight, which causes the brick to fall after a long distance.