# Properties of Liquids The most prominent properties of liquids are: - Viscosity - Cohesion - Adhesion - Surface Tension - Capillary Action ## Viscosity The **viscosity** of a liquid is a measure of it's resistance to flow. Liquids with a *low viscosity* would **flow freely** (water, gasoline, etc.). Liquids with a *high viscosity* would **flow slowly** (honey, syrup, motor oil, etc.) > Several factors can impact the rate at which a liquid flows: > 1. The IMFs between the molecules of a liquid > 2. The size and shape of the molecules > 3. The temperature of the liquid and/or its environment ![[ConventionalFormalCoqui-size_restricted.gif]] We could potentially measure viscosity by measuring: 1. the **rate at which an object falls** through a liquid (a metal ball will fall more slowly through a more viscous liquid) 2. the **rate at which a liquid flows** through through a narrow tube (the more viscous the liquid, the slower it will flow.) ## Cohesion The various [[Intermolecular Forces]] between **identical** molecules of a substance are examples of **cohesive forces**. ![[Pasted image 20220603110337.png]] The molecules within a liquid are surrounded by other molecules are are attracted equally in all directions by the cohesive forces within the liquid. However, the molecules on the surface of a liquid are only attracted by about one-half as many molecules. ## Adhesion The [[Intermolecular Forces]] between two **different** are called **adhesive forces**. ![[Pasted image 20220603111757.jpg]] > Consider what happens when water comes into constact with some surface: > > **If the adhesive forces** molecules between water molecules and the molecules of the surface **are weak compared to the cohesive forces** between the water molecules, the water **does not "wet"** the surface. ## Surface Tension **Surface tension** is defined as the energy required to increase the surface area of a liquid, or the force required to increase the length of a liquid surface by a given amount. ![[tumblr_nrw6uggUjw1tpri36o1_500.gif]] > As seen in this GIF, the [[Intermolecular Forces]] of water are extremely powerful, making its surface tension very high. > > The mass of the insect is not large enough to overcome these forces, which allows it to walk on the water rather than sink. This results from the cohesive forces between molecules at the surface of a liquid, and it causes the surface of a liquid to behavve like a stretched rubber membrane. ## Capillary Action **Capillary action** is when a liquid flows within a porous material due to the attraction of the liquid molecules to the surface of the material (**adhesive forces**) and to other liquid molecules (**cohesive forces**). ![[mmmEvi.gif]] The adhesive forces between the liquid and the porous material, combined with the cohesive forces within the liquid, may be strong enough to move the liquid upward against gravity. > [!info]+ Calculating Capillary Rise > ![[Pasted image 20220701210054.png|500]] > > The height to which a liquid will rise in a capillary tube is determined by the following equation: > > $h= \frac{2T \cos \theta}{r \rho g}$ > > $h$ = *height* of the liquid inside the capillary tube relative to the surface of the liquid outside the tube > $T$ = *surface tension* of the liquid > $\theta$ = *angle* of contact between the liquid and the tube > $r$ = *radius* of the capillary tube > $\rho$ = *density* of the liquid > $g$ = *acceleration* due to gravity (on earth this would be $9.8 \text{ m/s}^2$) [Capillary Rise Question](https://www.concepts-of-physics.com/mechanics/capillary-rise.php#:~:text=A%20liquid%20of%20density%20%CF%81,meniscus%20with%20the%20capillary's%20surface.)