Short Answer

Temperature affects surface tension by weakening it. As temperature increases, the molecules of a liquid move faster and the attractive forces between them become weaker. This reduces the surface tension and makes the liquid surface less tight.

When temperature decreases, the movement of molecules slows down and the attractive forces become stronger. This increases the surface tension. Therefore, surface tension decreases with an increase in temperature and increases when temperature decreases.

Detailed Explanation :

Temperature affect surface tension

Surface tension is the property of a liquid that makes its surface behave like a stretched elastic sheet. It exists because of the strong attractive forces (cohesive forces) between molecules at the surface. One important factor that affects surface tension is temperature. Temperature changes the amount of energy in the liquid molecules, which directly affects how strongly they attract one another.

When temperature increases, the surface tension of a liquid decreases. When temperature decreases, the surface tension increases. This relationship is observed in all liquids and plays a major role in natural processes, industrial applications, and everyday activities.

1. Increase in temperature decreases surface tension

When a liquid is heated, its molecules gain kinetic energy. This makes them move faster and vibrate more. Because of this:

• The attractive forces between molecules weaken
• Molecules at the surface can move apart easily
• The surface becomes less tight

As a result, the surface tension decreases. This is why hot water forms weaker and flatter droplets compared to cold water.

Example:

• Water at room temperature has higher surface tension than hot water.
• Soap bubbles burst easily in hot water because the surface tension is low.

2. Molecular explanation

Surface tension depends on the strength of cohesive forces between molecules. At higher temperature:

• Molecules move energetically
• They overcome the attractive forces
• Cohesive forces weaken
• The surface becomes less stable

Therefore, a rise in temperature always reduces surface tension.

At lower temperature:

• Molecules have less energy
• They move slowly
• Attraction between them becomes strong
• The surface becomes tighter

This increases surface tension.

3. Surface tension and droplet formation

Temperature affects the shape and behavior of droplets:

• Cold water droplets are round and firm due to high surface tension.
• Hot water droplets are flatter and spread out because their surface tension is low.

This is why cold water beads up on a leaf more clearly than warm water.

4. Effect on capillary action

Surface tension helps liquids rise in narrow tubes (capillary action). When temperature increases:

• Surface tension decreases
• Capillary rise becomes lower

That is why warm water climbs less in thin tubes than cold water.

This effect is important in plants because they depend on capillary action to transport water.

5. Effect on insects walking on water

Many small insects rely on the high surface tension of water to walk on it. When water becomes warmer:

• Surface tension decreases
• The surface cannot support weight as well

Some insects may find it difficult to stay on water if the temperature rises too much.

6. Effect on soap and detergents

Hot water allows soap to mix more easily because:

• Lower surface tension helps water spread quickly
• Cleaning becomes more effective
  This is why washing with warm water removes stains faster.

7. Industrial and scientific importance

Temperature control of surface tension is important in:

• Painting
• Printing
• Ink spreading
• Lubrication
• Bubble and foam formation
• Manufacturing of liquids

Surface tension affects how liquids spread, stick, and move on surfaces.

8. Examples from daily life
9. Hot tea cools faster

Hot tea has lower surface tension. This makes evaporation faster and helps the tea cool down quicker.

1. Oil spreads more when heated

Hot oil has lower surface tension, so it spreads easily in a pan.

1. Milk boils over

Hot milk has low surface tension. This makes bubbles form and rise quickly, causing it to overflow.

These examples show how temperature and surface tension are connected.

Conclusion

Temperature has a strong effect on surface tension. When temperature increases, molecules move faster, cohesive forces weaken, and surface tension decreases. When temperature decreases, molecules move slowly, forces become stronger, and surface tension increases. This change affects droplet formation, capillary action, insect movement, cleaning, and many everyday processes. Thus, understanding how temperature affects surface tension helps explain many natural and practical phenomena.