Surface Tension Fundamentals Quiz

Surface tension comes from cohesive forces between molecules at the surface. Because surface molecules are pulled inward more than outward, the surface behaves like a tight 'skin.'

Cohesion is attraction between like molecules (water–water, for example). At the surface, this attraction creates an inward pull that produces surface tension.

Soap molecules disrupt cohesive interactions at the surface. That lowers surface tension and makes the surface easier to deform.

Surface tension acts like an energy cost per unit area. Minimising surface area reduces surface energy, so droplets tend toward round shapes.

When adhesion to a surface is weak, water prefers to stick to itself. Strong cohesion plus weak adhesion leads to a more 'beaded' droplet.

Strong adhesion pulls liquid molecules toward the surface. This encourages spreading and produces a smaller contact angle.

If adhesion to glass is strong (like water on clean glass), the edges climb, giving a concave meniscus. If cohesion dominates (like mercury), the meniscus is convex.

A smaller contact angle generally means better wetting and more spreading. A larger contact angle corresponds to poor wetting and more beading.

Lower surface tension makes it easier for the liquid to spread and follow surface details. That’s why detergents help cleaning by improving wetting.

Higher surface tension more strongly penalises surface area. That favours rounder droplets and more stable curved surfaces.

Heating increases molecular motion, weakening the effective cohesion at the surface. That typically lowers surface tension.

Surface tension can be thought of as force along a line at the surface. This is why it’s often given in n/m.

With lower surface tension, the 'cost' of surface area is smaller. The liquid can spread more easily because the surface resists deformation less.

Creating more surface area requires energy because surface molecules are in a higher-energy state. That’s why systems tend to reduce surface area.

When adhesion to glass is strong, water is pulled toward the glass surface. That can make the liquid edge rise, shaping a concave meniscus.

Hydrophobic surfaces reduce adhesion with water. Water then beads up, giving a larger contact angle.

Soap lowers surface tension and helps stabilise the thin water film by reducing how quickly it drains and breaks. This allows bubbles to form and last longer.

Surface tension acts to reduce surface area and resist deformation. This often makes small disturbances flatten out.

Surface tension arises from intermolecular attractions and the imbalance of forces on surface molecules. Container shape can influence the visible shape, but not the origin.

Surface tension is a property of the liquid (and its temperature/composition). Different values change how strongly the liquid resists surface area and curvature, altering droplet shape.