Friction, drag and terminal velocity
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 7 practice questions, 1 real past-paper question with the answer explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Why do things slow down?
- Friction
- Drag
Read the transcript of the teaching part
Last time
Before we start: last time, in Circular motion, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Why do things slow down?
A cyclist stops pedalling and the bike slowly stops. Something is pushing against the motion. That something is friction, and its cousin, drag. Both always oppose the motion.
Friction
Friction is a force that acts between two surfaces in contact, and it opposes the motion, or the tendency to move. It acts in the opposite direction to the movement. Friction turns kinetic energy into thermal energy, so rubbing surfaces warm up. Rough surfaces give more friction than smooth surfaces. Oil or water between them reduces it.
Drag
Drag is the resistance to movement through a fluid, which means a liquid or a gas. Air resistance is drag in air, and water resistance is drag in water. Drag gets bigger as the speed increases, and it also depends on the shape. That is why cars, cyclists and planes have a streamlined shape: a smooth shape that reduces drag.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Friction and drag · Terminal velocity.
Chapter 1.5: Forces
- Balanced forces and F = ma 6 min
- Newton's third law 5 min
- Friction, drag and terminal velocity 5 min
- Thinking, braking and stopping distance 6 min
- Circular motion 5 min
- Springs: load–extension graphs 5 min
- Moments, balance and stability 5 min
Also for O Level Physics 5054
Which topics come up most in O Level Physics 5054 past papers, counted from every paper since 2004.