Friction is the quiet opponent of every moving thing. It lets you walk and lets brakes work, yet it also wears parts down and wastes energy as heat. In air and water it has a faster growing cousin: drag, which bites harder the quicker you go.
Friction is a force that opposes the relative motion of two solid surfaces in contact. Drag (air or water resistance) is the resistive force on an object moving through a fluid. Drag increases sharply as the object speeds up, while solid sliding friction stays roughly constant.
Friction is the force that opposes the relative motion of two surfaces in contact.
Drag (air or water resistance) is the resistive force on an object moving through a fluid.
Drive the object across different surfaces and through the air. Watch the resistive arrow: rougher surfaces give more friction, and as the speed rises the drag arrow grows while the sliding-friction arrow barely changes.
Four quick checks on what these forces are, their direction, and how drag changes with speed. Each correct answer earns XP and lights this skill on your star map.
Friction is a force that...
A box slides to the right across a floor. The friction force on the box acts...
Drag is the name for the resistive force on an object...
Compared with the same car driven slowly, a fast moving car experiences...
| Friction | Drag | |
|---|---|---|
| What it is | opposes relative motion of two solid surfaces | resistive force in a fluid (air or water) |
| Where it acts | between solid surfaces in contact | on objects moving through a fluid |
| As speed rises | stays roughly constant | increases sharply |
| Direction | opposite to the direction of motion | |
A car has a forward driving force of 800 N and is travelling at a constant speed along a level road. State the total resistive force (friction plus drag) acting on it, and explain.
On a moving object, friction and drag act opposite to the direction of motion, never along it. A common slip is to draw friction helping the motion. It always resists relative motion. Drag also increases with speed, so the resistive force on a fast moving car is much larger than on a slow one.
Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 1.
Which of these is a useful effect of friction?
The main difference between sliding friction and drag is that...
When a moving object is slowed by friction, its kinetic energy is mainly transferred to...
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