Surface Tension Investigation Using Water Striders Made from Paper Clips and Toothpicks
Science Lab · Grade 7
Shared by a teacher · Free to use as a template on AssessmentWiz.
Type
science_lab
Pre Lab
Background: Have you ever watched a water strider glide effortlessly across a pond without sinking? These insects seem to defy gravity, but the secret lies in a remarkable property of water called **surface tension**. Water molecules are strongly attracted to each other through a force called **cohesion** — the tendency of like molecules to stick together. At the surface of water, molecules cannot bond with molecules above them (because there is only air), so they pull extra tightly to their neighbors on the sides and below. This creates a thin, elastic-like 'skin' at the water's surface that can support small objects.
Water also exhibits **adhesion**, which is the attraction between water molecules and molecules of a different substance. For example, water clings to the side of a glass because water molecules are attracted to the glass molecules. Both cohesion and adhesion are special **water properties** that arise because water is a polar molecule — meaning it has a slightly positive end and a slightly negative end, which allows water molecules to attract each other like tiny magnets. This polarity is the root cause of surface tension.
Surface tension can be disrupted by adding certain chemicals called surfactants, such as dish soap. Soap molecules have one end that is attracted to water and one end that repels water. When soap is added, soap molecules wedge between water molecules, weakening the cohesive forces and reducing surface tension. This is why soap is effective at cleaning — it allows water to spread out and penetrate surfaces more easily. In this lab, you will build a model 'water strider' from paper clips and toothpicks to investigate how surface tension supports objects and how soap changes that ability.
Vocabulary
Term: Surface tension
Definition: The elastic-like force at the surface of a liquid caused by cohesion between liquid molecules, which allows the surface to resist external forces.
Term: Cohesion
Lab Type
Post Lab
Standards
Safety Level
Teacher Notes
Estimated Time
Experiment Design
Research Question
Learning Objectives
Preview shown. The full assessment (all questions, answer key, and teacher notes) loads with the page.