Water Suspension - Surface Tension

This science project Water Suspension requires only household materials. Everyone. Everyone probably gets materials at hand. Let’s explore the surface tension world now.

Age: 3+          Time: <10min

 Safety 

1. Adult supervision.
2. Be careful, the child may swallow the toothpick.
3. Put a container under to avoid making the floor slippery when you demonstrate this experiment.

 Materials List 

• Glass bottle （any glass container with a small mouth）
• Toothpicks
• Water
• Gauze
• Rubber band

 Instruction 

Step 1/3 – Fill the glass bottle fully with water.

Step 2/3 – Put the gauze over the bottle mouth and secure it with a rubber band.

Step 3/3 – Block the bottle mouth with your palm, Turn the glass bottle upside down, make sure that the upside-down bottle is at the water level. and Let go off your palm. (the water won't flow out of the bottle due to surface tension). Then insert the toothpick from the gauze. When the toothpick completely enters the water, it will float upwards and finally float on the water.

 Troubleshooting 

1. Why the water flow out of the bottle?
—Make sure that the upside-down bottle is at the water level.

 Scientific Description 

There are two scientific principles behind this experiment. The surface tension of the water holds the water together to form a water seal between each small openings in the gauze.
At micro level, the molecules of water are joined together (through cohesion) to form a thin membrane between each tiny opening on the screen. This is called cohesion. If you give the bottle a click, the seal will be broken and the water will run out off for it damaged the seal. The toothpick is made of wood which is less dense than the water. Thus when you insert a toothpick into the water, it will float on top of the water. 

 Extensions 

Can you use an index card to stop the water running out just like the gauze does?