- 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:
Remember to consider drag forces in your calculation for the resultant force. More details of this are in the notes “Force and acceleration”.
- 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
If a question considers air resistance to be ‘negligible’ this means in that question, air resistance is taken to be so small it will not make a difference to the motion of the body. You can take this to mean there are no drag forces acting on the body.