Measure Surface Tension with a Penny Quiz

What is the main concept being explored in the activity described in the text?

• Magnetism

• Gravity

• Surface tension

• Electricity

Answer explanation

The activity focuses on surface tension, which is the cohesive force at the surface of a liquid that allows it to resist external force. This concept is key to understanding how liquids behave in various situations.

What material is used to decrease the surface tension of water in the experiment?

• Salt

• Sugar

• Soap

• Vinegar

Answer explanation

Soap is used to decrease the surface tension of water because it contains surfactants that disrupt the cohesive forces between water molecules, allowing the water to spread more easily. This is why soap is the correct answer.

What tool is used to add water drops to the penny?

• Straw

• Spoon

• Medicine dropper

• Syringe

Answer explanation

The medicine dropper is specifically designed to add small amounts of liquid, like water drops, accurately. A straw, spoon, or syringe may not provide the same precision for this task.

Why do water droplets form on a surface instead of spreading out evenly?

• Because of gravity

• Because of surface tension

• Because of air pressure

• Because of temperature

Answer explanation

Water droplets form on a surface due to surface tension, which causes the liquid to minimize its surface area. This results in droplets rather than an even spread, as the cohesive forces between water molecules pull them together.

What happens to the water droplet on the penny when soap is added to the water?

• The droplet changes color

• The droplet evaporates

• The droplet gets larger

• The droplet gets smaller

Answer explanation

When soap is added to the water droplet on the penny, it reduces the surface tension of the water. This causes the droplet to spread out and get smaller, rather than evaporate or change color.

What is the purpose of drying off the penny and surrounding surface after the first part of the experiment?

• To make the penny shiny

• To clean the penny

• To ensure accurate results in the next part of the experiment

• To measure the weight of the penny

Answer explanation

Drying off the penny and surrounding surface is crucial to ensure accurate results in the next part of the experiment. Any moisture could affect measurements or reactions, leading to unreliable data.

What is a surfactant?

• A material that increases the surface tension of a liquid

• A material that decreases the surface tension of a liquid

• A type of molecule found in water

• A type of soap

Answer explanation

A surfactant is a material that decreases the surface tension of a liquid, allowing it to spread more easily. This property is essential in various applications, including detergents and emulsifiers.

What should you do if you want to try the experiment with different liquids?

• Change the medicine dropper

• Get an adult's approval

• Use a different penny

• Use only water

Answer explanation

To safely experiment with different liquids, it's important to get an adult's approval. This ensures safety and proper guidance during the experiment.

What is the main idea of this reading?

Draw a water molecule showing the charges on each atom.