Drag Force & Air Resistance (CIE AS Physics)

• Drag forces are forces acting the opposite direction to an object moving through a fluid (either gas or liquid)
• Examples of drag forces are friction and air resistance
• A key component of drag forces is it increases with the speed of the object. This is shown in the diagram below:

Frictional forces on a car increase with its speed

• Air resistance is an example of a drag force which objects experience when moving through the air
• At a walking pace, a person rarely experiences the effects of air resistance
• However, a person swimming at the same pace uses up much more energy - this is because air is 800 times less dense than water
• Air resistance depends on the shape of the body (object) and the speed it’s travelling
• Since drag force increases with speed, air resistance becomes important when objects move faster

A racing cyclist adopts a more streamline posture to reduce the effects of air resistance. The cycle, clothing and helmet are designed to allow them to go as fast as possible