CIE A Level Physics复习笔记3.1.6 Drag Force & Air Resistance
Drag Forces
- 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
Worked Example
A car of mass 800 kg has a horizontal driving force of 3 kN acting on it.Its acceleration is 2.0 m s-2.What is the frictional force acting on the car?
Exam Tip
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
- 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
Exam Tip
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.
转载自savemyexams
国际竞赛真题资料-点击免费领取！
美高学分项目重磅来袭！立即了解
2025欧几里得数学竞赛报名开启！
