Category Archives: Surface Tension

Needle Through a Balloon

Demo: FM-A-NB
Pira Index: 2B 30.00

Lab Equipment  Directions
  1. balloon
  2. knitting needle
  3. base to hold needle
  4. vaseline
  1. Blow up the balloon.
  2. Lubricate the point of the needle with vaseline and slowly insert it into the inlet or neck of the balloon where the rubber is slightly thickened. Push the needle on into the balloon and through the thickened part on the opposite side.

You may need to lubricate both ends of the balloon as well. Practice is recommended.

Surface Tension

Demo: FM-A-ST
Pira Index: 2A 10.69

 Lab Equipment  Directions
  1.  floating device
  2. 2000ml beaker
  3. soap
  1.  Fill the beaker with water.
  2. Place the device in the water so that the rim stays on the surface of the water.
  3. Add a small amount of soap to the water and watch the floater rise.

 

Surface Tension Bottles

Demo: FM-A-SB
Pira Index: 2A 10.60

 Lab Equipment  Directions
  1.  special drink bottle with lid
  2. special jar with netting cover
  3. plastic plate
  4. a ‘salad bowl’ container to catch water
  5. 1 gallon of water
 Fill the bottle with water first and do not let the students see that these bottles are specially designed until after the demo.

  1. Hold drink bottle upside down (over a sink or bowl). Carefully remove the lid without tilting and the water does not run out. Push the pencil inside the hidden hole in the plexiglas, then let go of the pencil. It floats up into the bottle.
  2. Hold the jar full of water upside down with a plastic plate holding the water in. Carefully slide the plate off the netting and the water stays in. Touch the netting and suddenly the water runs out.

 

Kubic Bubbles

Demo: FM-A-KB
Pira Index: 2A 10.50

 Lab Equipment  Directions
  1.  plastic frames
  2. plexiglas plates and suction spacers
  3. soap bubble solution (~1 gallon)
  4. solution holding tank (mixing bowl)
  1.  Pour soap solution into bowl. Stick frame into solution and slowly pull it out.
  2. Watch as the films change shape to reach the minimal surface tension.
  3. Repeat with a different shape or put only 2 surfaces in at a time and compare.
  4. Plates (#2) can be used to show minimum surface area originating from either 3 or 4 points depending on the placement of the spacers.

 

Cohesion Plates

Demo: FM-A-CP
Pira Index: 2A 10.35

 Lab Equipment  Directions
  1.  Cohesion disks
Note: Careful not to damage the surface of these plates. They must be kept smooth and clean. Make sure these plates are thoroughly dried before putting away.
  1.  Place the disks together and try to pull them straight apart.
  2. Place 2 drop of water on one of the plates, put them together and move them around to spread water evenly.
  3. Compare the force of attraction with step #1.

 

Air Pressure Balloons

Demo: FM-A-AP
Pira Index: 2A 10.52

 Lab Equipment  Directions
  1.  stopcock
  2. two identical balloons
  3. rubber bands
  1.  Blow air into two balloons, leaving one balloon noticeably smaller.
  2. Attach balloons to stopcock using rubber bands to prevent leaking.
  3. Turn stopcock to open position.
  4. Observe that the smaller balloon blows up the larger balloon. Why?

Cohesion Plates

Demo Code: FM-A-CP
Pira Index: 2A 10.35

Molecular cohesion holds two metal disks together.

 LAB EQUIPMENT

  1. Cohesion disks
DIRECTIONS

  1. Place the disks tightly together and let them hang from one handle being careful not to let them slide apart or fall & get damaged.

Notes: Careful not to damage the surface of these plates. They must be kept smooth & clean. Make sure these plates are thoroughly dried before putting away.

Capillary Action

Demo Code: FM-A-CA
Pira Index: 2A 20.10

Demonstrates the principles of pressure and energy.

 LAB EQUIPMENT

  1. Capillary set with support
  2. Colored Water
DIRECTIONS

  1. Fill lower tray with water.
  2. Note that the fluid rises higher in the small tubes than the large ones.

Notes:

Air Pressure Balloons

Demo Code: FM-A-AP
Pira Index: 2A 10.52

Demonstrates the principles of pressure and energy.

 LAB EQUIPMENT

  1. Stopcock
  2. Two identical balloons
  3. Rubber bands
DIRECTIONS

  1. Blow air into two balloons, leaving one balloon noticeably smaller.
  2. Attach balloons to stopcock using rubber bands to prevent leaking.
  3. Turn stopcock to open position.
  4. Observe that the smaller balloon blows up the larger balloon.  Why?

Notes: