2 Mechanics - Pearson Global Schools

6. Air resistanceAir resistance is the force that opposes the motion of bodies through the air. Thisforce is dependent on the speed, size and shape of the body.Speed skiers wear special clothes andsquat down like this to reduce airresistance.Free body diagramsProblems often involve more than one body and more than one force. To keepthings simple we always draw each body separately and only the forces acting onthat body, not the forces that body exerts on something else. This is called a freebody diagram.Figure 2.30NFA good example of this is a block resting on a rampas shown in Figure 2.30. The block will also exerta force on the slope but this is not shown, since itis a free body diagram of the block not the ramp.Another common example that we will come acrossmany times is a mass swinging on the end of a rope,as shown in Figure 2.31.Fixed endTFigure 2.31WWExercise17 Draw free body diagrams for(a) a box resting on the floor(b) the examples shown belowiii(c) a free fall parachutist falling through the air(d) a boat floating in water.33