Year 10 Assembly Science Experiment

Senior School | 18.03.2019

Year 10 students, Elliot Lindop, Jacob McCahill and Sam Moss led our Monday morning Headmaster’s Assembly on the theme of National Science Week.  With the help of Mr Chorley, Head of Science, the boys carried out a practical experiment in front of the Senior School.  This took great courage and skill.  The team expertly demonstrated that they could make a quantity of water in a glass bottle boil by pumping air out of the bottle, but without its temperature being increased!

An explanation of why the water boiled without heating it:

There are a number of forces acting on the water inside the bottle. One of them is caused by atmospheric pressure. This atmospheric pressure is the force of the air inside the bottle of water pressing down on a certain area. This “pressing ” helps to push down the molecules in the water and stops them from escaping.

Molecules in the water are constantly moving and hence, they carry a certain amount of kinetic energy. When the pressure in the bottle is reduced by pumping air out of the bottle, the molecules in the water do not need as much kinetic energy as they needed before to escape from the liquid. Hence, the kinetic energy they already contain is sufficient for them to overcome the atmospheric pressure and escape the intermolecular forces of the water.

CONCLUSION: The water boils without its temperature being increased, because the pressure on the liquid from the air above is reduced.