Illustration of oil spreading
Practical Activity for 14-16
This helps students to remember that olive oil molecules stick up out of water like grass on a lawn.
Apparatus and Materials
- Transparent trough
- Drinking straws
Health & Safety and Technical Notes
The drinking straws are cut into similar lengths of about 2.5 cm. Roll a plug of Plasticine and force it into one end of each of the small lengths, closing that end and making a loaded cylinder. The amount of Plasticine used determines whether the straws float or sink. Once you find the right amount, the straws will float upright and bob up and down in the water if disturbed.
- Drop a handful of about fifty of the loaded straws into water, from about 10 cm above the water surface. Observe the behaviour.
Photo courtesy of Mike Vetterlein
- The straws should float upright and congregate together just like an oil film.
- The patch is one straw deep - that is significant.
- Olive oil has a long molecule. One end attaches to water and the other end is inert.
This experiment was safety-tested in July 2006