Fluid friction is the resistance to an object's motion through a liquid or gas. When the motion is occurring in a liquid, it is referred to as viscous resistance. Resistance to an object moving through a gas, such as air, is termed air friction.
The concepts of fluid friction vary depending on whether the motion is taking place in a liquid or gas. One item that both media share is that the resistance to motion contributes to an object reaching its terminal velocity. This occurs when the resistance from a gas or fluid is equal to the weight of the object, and it remains constant until another force is introduced.
For motion in a liquid, viscous resistance caused by a drag force is proportional to the velocity of the object at slow speeds. This drag force is based on the object's geometry and the viscosity of the liquid, which can vary between fluids. For motion through air, friction at slow speeds is proportional to the velocity. At higher speeds, the drag force depends on the cross-sectional area of an object, the object's density and the drag coefficient. This drag force has a negative value, as the resistance is always opposite the direction of velocity.Learn More
Static friction is the resistance to movement when two non-moving solid objects are in contact with each other. Static friction matches applied force and prevents motion. When the applied force overcomes static friction, the object starts moving, and at this point, static friction ceases and kinetic friction comes into play.Full Answer >
According to the Mayo Clinic, skin friction occurs when the skin is resistant to motion, which in turn can lead to bedsores and skin injury. Skin friction is a common reaction to the skin being dragged across surfaces. Skin friction is typically more severe when the skin is moist.Full Answer >
In roller coasters, friction is a force that opposes motion and significantly slows the cars as they move on the track. While it is easy to believe that friction is bad for the ride, it is one of the forces engineers consider in ensuring passengers have a safe ride.Full Answer >
Friction allows objects in motion to return to a state of rest. Without friction, an object set in motion would be unable to stop moving.Full Answer >