Flow Rate and Viscosity a liquids resistance to flow (its thickness or thinness) is called ______ a thicker a liquid is, the more _______ it Is. the time.

Flow Rate and Viscosity

a liquids resistance to flow (its thickness or thinness) is called ______

a thicker a liquid is, the more _______ it Is.

the time it takes for a fluid to flow over a set distance is called ___________

Flow Rate and Viscosity

a liquids resistance to flow (its thickness or thinness) is called viscosity

a thicker a liquid is, the more viscous it is

the time it takes for a fluid to flow over a set distance is called flow rate

Product Performance and Viscosity

viscosity is measured precisely in many industries (paint, cosmetics)

nail polish goes on smooth and dries to a solid, while mascara is thick and dries quickly. The viscosity of these liquids is controlled by a solvent

a solvent keeps the ingredients of the mixtures dissolved, then it evaporates

Product Appeal and Viscosity

heat affects viscosity because it thins out the fluid, making it less viscous

food manufacturers consider viscosity in order to make their product marketable (a candy that is too hard will not sell)

Applications – paint stripper would drip off before it had a chance to remove the paint, so the viscosity is increased to improve its performance

a chef will thicken or thin gravy, or sauce, by adding, or taking away more solvent (water)

mechanics must adjust the viscosity of oil depending on the season of the year

Others?

How Does the Viscosity of Liquids Vary?

liquids flow at different rates because they have different viscosities

as temperature increases, the ________ forces between the particles is less, so the viscosity of a liquid ________ as it is HEATED and ________ when it is COOLED.

How Does the Viscosity of Liquids Vary?

liquids flow at different rates because they have different viscosities

as temperature increases, the attractive forces between the particles is less, so the viscosity of a liquid DECREASES as it is HEATED and INCREASES when it is COOLED.

Viscosity Comparisons

The more friction - the more viscous (thicker) a substance is.The higher the viscosity of a substance, the slower it flows.

How Does the Viscosity of Gases Vary?

gas particles flow differently than liquid particles, because they are so far apart and the attractive forces between the particles are very low

instead of sliding past each other (as they do in a liquid), the particles of a gas are more likely to collide (increasing the resistance to flow and therefore increasing the viscosity)

temperature has a direct effect on viscosity of a gas - as temperature increases, the attractive forces between the particles is less, so the viscosity of a gas INCREASES as it is HEATED and DECREASES when it is COOLED

Density of Fluids

Density is the amount of matter in a given volume.

The density of a substance depends on the particles it is made up of. When we talk about density, it's usually mass density we're referring to. The mass density of an object is simply its mass divided by its volume.

Density of Fluids

Substances that have a higher density than the density of the substance it is placed in will sink; substances that have a lower density than the density of the substance it is placed in will float.

Question

Why does cooking oil float on water and why does lead float on liquid mercury?

Answer: the particles of the matter floating on top are less dense that the matter they are floating on.

ANSWER

Why does cooking oil float on water and why does lead float on liquid mercury?

Answer: the particles of the matter floating on top are less dense that the matter they are floating on.

Density is the amount of matter in a given volume.

What does this Mean?

Calculating Density

Density is the mass of a substance divided by its volume, which changes as temperature changes. This is shown in the following equation form:

Density (d) = mass (m) / volume (V) (d) = 1.0g/1ml (d) = 1.0g/ml

Calculating Density

Simply cover up whichever value you need to calculate and the other two are shown in their proper placement, be it to multiply or to divide.

Calculating Density

MASS = d x V

density = M/V

VOLUME = M/d

Calculating Density

For example: cover up the M. This leaves you with d/V (ignore the fact that it is in the denominator).

Density times volume will give you mass. You can also check it out by way of the units:

(g / cm3) x cm3 cancels out the volume unit leaving grams, the desired unit for mass.

solids: d = grams/cubic centimeters ( g/cm3 )

liquids: d = grams/milliliters ( g/ml )

Practice Problems

Problem 1 Mass = 37g Volume = 107 ml Find the density

Problem 2 d =2.70g/ml Volume =1L Find the Mass

• Problem 3• Mass =1.7Kg• density = 11.3 g/ml• Find the Volume

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Buoyancy

Why do we float?

Buoyancy

Buoyancy is the tendency for materials to rise or float in a fluid.

The upward force exerted on an object in a fluid is referred to as the buoyant force. This allows for something to float in a fluid.

Can you give examples of things that are buoyant in different fluids?

________________in ________________ ________________in ________________

How Buoyancy and Density are Related

- The buoyant force of a liquid does not depend on physical state, but rather on density (This is also true for buoyancy in gases)

- the relationship between buoyancy and density is the basis for the hydrometer, which is an instrument designed to measure density directly

- the higher the hydrometer floats in the liquid being tested, the higher the density is (of the liquid)

How Buoyancy and Density are Related

- hydrometers are used widely in the food and beverage industries

- besides density, hydrometers can also (indirectly) measure sugar content of canned fruit syrup or alcohol content of wine

Archimedes. Principle

- states that: the buoyant force acting on an object equals the weight (force of gravity) of the fluid displaced by the object.

- used his own body (which displaced water in the bathtub) to prove the king's goldsmith was cheating the king

- the buoyant force does not depend on the weight of the submerged object, but rather on the weight of the displaced fluid