#Viscosity meaning in science skin#

The viscosity of the fluid or the coefficient of viscosity. It depends on the viscosity of the fluid. So the faster I pull the lid, well, the faster I'm gonnaīe pulling this water, the bigger that force which means the bigger the viscous force, which was proportional And something else that it depends on is the speed with which you drag the lid. The bigger that area, the more fluid you're gonna be dragging, the larger the viscousįorce that makes sense so it's this area here. So it's only that part of the lid that's actually in contact with the fluid. So if you imagine theĭimensions of this box would only expand here. It's just the area of the lid that's actually in contact with the fluid. So, what does this depend on? What does this viscous force depend on? One thing it depends on is the area and not the whole area of the lid. To the left on the lid and I'm gonna call this a viscous force. To the right on the fluid, then the fluid is gonna exert a force by doing its third law Why this lid slowed down when we gave it a nudge, it was dragging that fluid along with it. Once you get down to the bottom well, now the fluid is in contact with this surface at the bottom and this surface at theīottom is not moving. Velocity of this fluid gets smaller and smaller. Pulls this third most layer and this keeps going down the line, and what you get is a velocity gradient is the fancy name for it. Layer gets pulled this way then the layer right below it gets pulled by the top most layer and the second most layer And so it resist the motionīut it's worse than that because if this top most There's adhesive forcesīetween this fluid and the lid on an atomic and molecular level, this fluid gets pulled with it. Was in contact with the lid caused this top most layer to start moving with the same speed as the lid. Was moving across the top, the fact that this fluid What do I mean by that? I mean that when this lid The fact that this fluid's in here now is resisting the motion You give it another nudge, it slows down and stops. It doesn't keep going, it slows down and stops. Now what happens is you take this lid, you go to slide it across again. And I'm gonna fill it to the brim all the way to the top. Let's say there is no resistance so that if I gave this lid a little nudge, it just keep moving Now, check out this lid that I can put on the empty box.

#Viscosity meaning in science skin#

Which shows how naïve we all are-what in the world is skin friction!? Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation.

Skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body. Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces. Dry friction is subdivided into static friction ('stiction') between non-moving surfaces, and kinetic friction between moving surfaces.įluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. You can't expect a simple equation to describe all instances of that behavior.ĭry friction resists relative lateral motion of two solid surfaces in contact. Basically electrons from different surfaces interact and create resistance. The force is really caused by quantum phenomena, the electromagnetic force. It's just that usually when you're talking about friction (such as air resistance) you don't usually think about layers of fluid but instead simplify the force as proportional to an object's velocity, such as F = k v or F = k v^2.į = μ N is just an approximation and only applies to dry friction. It may still be hard to believe there is zero resistance, but even if there was another resistance force, by definition it is not the viscous force, but some other force we had assumed didn't exist.

The 'inertial drag' has nothing to do with velocity, only acceleration, and therefore is not viscosity. But still, you can't blame the mathematics.īesides, if the board and water are already moving, there sure is no resistance. So the water increases inertia, but doesn't provide a resistance force.Įxcept with a depth of infinity the mass would probably be infinity too, so it would be impossible to drag the water (a = F/m = F/∞ = 0).

If the board is 1 kg, the water is 2 kg, and the force pushing the board is 6 N, then acceleration is not 6 N / 1 kg = 6 m/s^2, as is the case when there is no water, but 6 N / (1 kg + 2 kg) = 2 m/s^2, with a = F/m. However, by dragging the water with us we need to conquer its inertia. There is no force preventing that because there is no 'ocean floor' to provide the friction, and we are assuming there is no other resistance. I think if the depth were really infinity, there would be no friction, because we could perfectly well drag all that water with us.