In physics, how does viscosity of a liquid effect how an object passes through it?

Question

Talking about dropping small spheres (such as ball bearings) through different viscositys of liquids such as "washing up liquid", "cooking oil" and "water":

Does anyone know a formulae or relationship that might apply to this?

Answer 1

Viscosity is the resistance to flow in an ideal fluid. Not all fluids are ideal (also called Newtonian). More on that later. If the flow is non turbulent (more on turbulence later, too), the relation between terminal velocity of a sphere dropping through a fluid and the viscosity is linear. This relation is:

F = 6*pi*r*u*v

Where F is the drag force. For an object dropping at constant velocity that is just the weight of the sphere minus the weight of fluid it has displaced. r is the sphere radius, u is the viscosity and v is the velocity. This can be rearranged and massaged to give:

v = 2 * g * r^2 * (Rhos - Rhof) / (9 * u)

Where g is the acceleration of gravity, Rhos is the density of the sphere and Rhof is the density of the fluid. You might notice that u has some unusual units. In SI units, u is measured in poise with 1 poise = 0.1 kg/(m * sec).

If you intend to do experiments to measure viscosity, be sure to use small ball bearings so they reach terminal (constant) velocity quickly and remain in the laminar (meaning not turbulent) flow range. After you do a test and determine the viscosity, you need to make sure it was laminar. You do this by calculating the Reynold's number:

Re = Rhof * v * 2 * r / u

This is a dimensionless number and should be below 2000 to assure your results are valid. If it is too big, use a smaller ball bearing and try again.

The one thing you will need that is hard for you to measure is the density of steel and the fluids. Almost all steels have about the same density (7.8 gm/cc) and most test liquids (oils, etc.) have the densities posted on the web. You can often find viscosities posted as well to help see if your results are reasonable.

One final comment, the concept of viscosity applied strictly refers to fluids that require no shear stress to begin moving and the motion is proportional to the stress applied. That is the definiton of a Newtonian fluid. Water is very close to this. Oil and washing up liquid are close as well. You can measure the viscosity of non-Newtonian fluid such as axle grease of shortening but the value measured will only be valid over a limited range of applied stress.

Answer 2

Viscosity is a measure of the resistance of a fluid to deform under shear stress. It is commonly perceived as "thickness", or resistance to pouring. Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. Thus, water is "thin", having a lower viscosity, while vegetable oil is "thick" having a higher viscosity. All real fluids (except superfluids) have some resistance to shear stress, but a fluid which has no resistance to shear stress is known as an ideal fluid

In general, in any flow, layers move at different velocities and the fluid's "thickness" arises from the shear stress between the layers that ultimately opposes any applied force

issac newton postulated that, for straight, parallel and uniform flow, the shear stress, τ, between layers is proportional to the velocity gradient, ∂u/∂y, in the direction perpendicular to the layers, in other words, the relative motion of the layers.

τ=∂u/∂y is a formula....

Here, the constant μ is known as the coefficient of viscosity,the viscosity, or the dynamic viscosity.
Many fluids, such as water and most gases, satisfy Newton's criterion and are known as Newtonian fluids. Non-Newtonian fluids exhibit a more complicated relationship between shear stress and velocity gradient than simple linearity.






.


.

Answer 3

F=6(pi)rnv

where r is the radius of the sphere, n is teh viscosity of the fluid, v is the velocity of the sphere, and F is the viscous drag force experienced by the sphere.

if you want to know more, do a search on Stoke's Law.

according to the expression, increased viscosity increases the drag force, so the descending particle reaches terminal velocity much quicker. (term. vel is reached when fluid upthrust is equalled by fluid drag force)

Answer 4

Mercury (Hg) is classed as liquid metal!
So as a rough guide (not a formula) just look at the problem this way.
An English brain is surrounded by Mercury,( its dense)!
A Scotsman's brain is surrounded by water (not at all dense)
An English brain will take forever to absorb knowledge, a Scotsman will absorb knowledge immediately!!
Hope this helps????

Answer 5

hahaah! if u're a budding author as ur nick suggests, then i guess you're in the wrong place to answer a question!

funny stuff!

Answer 6

friction