Lesson 5.2: Surface Tension
Accompanying Lesson Plan: Lesson 5.2: Surface Tension
Video
Water’s Surface Tension
- The paper clip is on the water but is not floating like a boat which is less dense than water.
- The paper clip is more dense than water but can rest on the surface of the water because of the water's surface tension.
Image
Water Strider and Water Molecules
- Evidence of water's surface tension can be seen where the water strider's legs dent but do not break through the water's surface.
- The attraction of polar water molecules to each other helps create water's strong surface tension.
Image
Why Water Beads
- The water molecules beneath the surface are pulled in all directions.
- The molecules at the surface are pulled together and in.
- This creates a tighter arrangement of molecules at the surface and the round shape of a drop of water.
Image
Water and Alcohol Molecules
- Alcohol has one O–H bond which is polar, but a large portion of the molecule is made up of C–H bonds which are nonpolar.
- Alcohol molecules do not attract each other as strongly as water molecules and have a weaker surface tension.
Image
Water and Detergent
- The charged end of a detergent molecule attracts water molecules at the surface in an outward direction.
- This disrupts the way the molecules normally attract at the surface and weakens the surface tension, causing the drop to collapse.
Video
Water on Paper Towel
- Paper is made from cellulose which is made of glucose molecules bonded together.
- Glucose has many O–H bonds which are polar.
- Polar water molecules are attracted to the polar cellulose and cling to it.
Video
Water on Wax Paper
- Wax is made of paraffin which is only carbon-hydrogen bonds.
- C–H bonds are not polar.
- Water is more attracted to itself than to the wax so it stays together and does not spread out or absorb into the wax paper.
