Problem 12 - An Introduction to Physical Science

Question

Choose the word or phrase that best answers the question. What property enables you to float a needle on water? A) viscosity B) temperature C) surface tension D) crystal structure

Step-by-Step Solution

Answer

C) surface tension

Step 1: Understand the Question

The question is asking about the property that enables a needle to float on water. Consider the characteristics of each option given.

Step 2: Evaluate Option A (Viscosity)

Viscosity is a measure of a fluid's resistance to flow. It does not directly enable solids to float on liquids.

Step 3: Evaluate Option B (Temperature)

Temperature affects the physical state of substances but does not directly cause floating unless through changing states of matter or creating convection currents.

Step 4: Evaluate Option C (Surface Tension)

Surface tension is the elastic tendency of a fluid surface which makes it acquire the least surface area possible. This property allows light objects to float on the surface of a liquid.

Step 5: Evaluate Option D (Crystal Structure)

Crystal structure refers to the arrangement of atoms, ions, or molecules in a crystalline material. This does not relate to floating on a fluid surface.

Step 6: Conclusion

Based on the evaluations, surface tension is the property that allows a needle to float on water by creating a surface film capable of supporting the needle's weight.

Key Concepts

physical properties of fluids

Fluids, such as liquids and gases, have unique characteristics that define their behavior and interaction with other substances. These properties include viscosity, density, and surface tension.

Viscosity: This is the measure of a fluid's resistance to flow. Think about how honey flows more slowly compared to water. Higher viscosity means the fluid is thicker and flows less easily.

Density: This property measures the mass per unit volume of a fluid. For example, oil is less dense than water, which is why it floats when both are mixed.

Surface Tension: This property is the elastic tendency of a fluid surface, which minimizes its surface area. Surface tension is what enables small objects, like needles or insects, to float on water without sinking.

surface tension in liquids

Surface tension is a fascinating property of liquids that results from the cohesive forces between molecules. It acts like a 'skin' on the surface of the liquid, holding it together.

Cohesive Forces: These are the attractive forces between molecules of the same substance. In water, hydrogen bonds hold the molecules tightly, leading to high surface tension.

• Water molecules stick together
• Makes the surface behave like an elastic sheet

Examples:

• Water droplets forming beads on a waxed car
• Insects like water striders walking on water
• Floating a needle on the water surface when placed carefully

Surface tension decreases with the increase in temperature, because the molecules move more rapidly and are less tightly bound.

floating objects on water

The principle of floating objects on water is closely related to surface tension and buoyancy. Here’s how it works:

Buoyancy: This is the force that supports objects in a fluid, making them float. For an object to float, the buoyant force must be equal to or greater than the object's weight.

Surface Tension in Action: Tiny objects, like a needle, can float due to surface tension.

• Needles: Placing a needle gently on the water without breaking the surface allows it to float, supported by the surface tension.
• Paper clips: Similarly, a paper clip can float if placed carefully on the water surface.

For both cases, breaking the surface tension (e.g., by adding soap) will cause the object to sink because the cohesive forces are disrupted. The interaction of these forces explains why only small, lightweight objects can float on water due to surface tension. Larger objects rely more on buoyancy, which involves the displacement of water to float.