1. Surface Tension & Capillary Action

2. A water strider bug skips across the surface of the water.
Surface Tension
Surface tension is the tightness across the surface of water that is caused by the polar molecules pulling on each other.
A water strider bug skips across the surface of the water.

3. Surface Tension
The molecules at the surface are being pulled by the molecules next to them and below them.
The pulling forces the surface of the water into a curved shape.

4. Surface Tension
You can see surface tension on your windshield when it rains. Raindrops will form round beads when they fall on the windshield.

5. Drops of Water on a Penny
Materials you will need:
1 penny
forceps (that is fancy for tweezers)
paper towel
cup of clean water
cup of soapy water
2 pipettes
Helpful tips:
Keep your clean water pipette in the clean water. Keep your soapy water pipette in the soapy water.
A drop is a small drip of water.

6. Capillary Action
The combined force of attraction among water molecules and with the molecules of surrounding materials is called capillary action.
Capillary action allows water to move through materials with pores or narrow spaces inside.

7. Capillary Action
Liquid will rise higher inside a straw than outside of the straw.
Water will climb up into the pores of a brick or piece of wood.

8. How does water defy the force of gravity?
Capillary Action
How does water defy the force of gravity?
Just as water molecules stick to each other, they also stick to the sides of a tube. As water molecules are attracted to the tube, they pull other water molecules up with them.
Let’s try it with a piece of wood.

9. Capillary Action
Water molecules also cling to the fibers of materials like paper or cloth.
Do you have any “wicking” clothing?
The capillary action that occurs along the cloth’s fibers pulls the water (sweat) away from your skin. The
fibers keep you dry.

10. Can you use a string to pour water sideways?
Capillary Action
Can you use a string to pour water sideways?
Try the “Try This” activity on page 25. Follow steps 1-4 and then answer the question when you complete the activity.

11. More examples of defying gravity.