![]() ![]() ![]() The amount of intermolecular interactions is also crucial in determining how tightly two molecules hold onto each other, and this factor is especially important in very weak London dispersion forces, where a small advantage goes a long way. The molecules are bigger, and so they experience more drag as they move through the liquid. The major difference between motor oil and gasoline is that the motor oil contains much longer hydrocarbon chains. ![]() The intermolecular attractions between the molecules are much weaker than those between sugar molecules they're just London dispersion forces. Motor oil and gasoline are composed of the same class of compounds, hydrocarbons, composed of carbon chains covered in hydrogen atoms. The motor oil example works in a similar way. As these molecules move past each other in the very concentrated solution, they cling to each other, slowing down the flow of the liquid. Sugars are covered in OH or hydroxyl groups that are capable of strong hydrogen bonds. The strong intermolecular attractions between the individual sugar molecules are also a major factor. Why is honey so viscous? Partly it's just that the sugar molecules in the water are much larger than the water molecules, so they experience a lot more drag as they move through the solution compared to just plain water. Nevertheless, this high viscosity is something honey has in common with polymer solutions, as well as with some oligomers, which are short-chain polymers that can be liquids instead of solids. The sugars aren't polymers, either they are simple monosaccharides such as glucose and fructose. It contains a little bit of water and a whole lot of sugars, plus other small molecules produced by the plants from which the bees gathered the nectar to make the honey. The honey doesn't flow very easily, especially compared to something like water. Viscosity is often described in very general terms as "resistance to flow". It resists the movement of the spoon when we stir it. When we say that, we mean that water is much easier to stir or to pour than honey. For example, we say that honey is more viscous than water. Viscosity is a term we use to describe the "thickness" of different liquids. Let's start with a property that you are probably familiar with. What makes them unique? Why do they have properties that aren't easily replicated by other materials? Polymers have come to occupy a very important niche in the materials we use every day. We shall concentrate on laminar flow for the remainder of this section, leaving certain aspects of turbulence for later sections.\) The drag both between adjacent layers of fluid and between the fluid and its surroundings forms swirls and eddies, if the speed is great enough. First, any obstruction or sharp corner, such as in a faucet, creates turbulence by imparting velocities perpendicular to the flow. Streamlines are smooth and continuous when flow is laminar, but break up and mix when flow is turbulent. The lines that are shown in many illustrations are the paths followed by small volumes of fluids. When there is turbulence, the layers mix, and there are significant velocities in directions other than the overall direction of flow. Layers flow without mixing when flow is laminar. (credit: Creativity103)įigure shows schematically how laminar and turbulent flow differ. If you watch the smoke (being careful not to breathe on it), you will notice that it rises more rapidly when flowing smoothly than after it becomes turbulent, implying that turbulence poses more resistance to flow. The smooth flow is called laminar flow, whereas the swirls and eddies typify turbulent flow. \): Smoke rises smoothly for a while and then begins to form swirls and eddies.
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