Kinetic theory of matter

Explaining the behaviour of matter using the idea of particles is a powerful and accurate theory however it is known to cause some conceptual challenges for some students. Being able to describe macroscopic behaviours in terms of a microscopic model that cannot be seen and moving between these two domains is not intuitive. You may wish to use the terms macro and micro and signpost which world you are in when teaching this subject until these ideas become established in the students’ minds and ways of working.

They need to know that kinetic theory of matter assumes all matter is made of small particles which are in random motion. By making simple assumptions about these particles a lot about the physical properties of matter and how it behaves can be explained. They need to identify three main phases of matter, solid, liquid and gas as well as to differentiate them by the different behaviours of the particles in each phase.

Gases are particularly well modelled this way and the behaviour of the particles allows us to deduce empirical relationships between the pressure, volume and temperature of the gas and to make testable predictions.

Similarly the meaning of density can be discussed for all three phases using kinetic theory, as well as to be able to consider the pressure exerted by a fluid such as water due to the height or depth of the fluid. Applying the formulae relating the quantities of mass, volume, density, pressure, depth of fluid and gravitational field strength; exploring how changes in these are inter-related revisits math skills.

Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS, SSERC or recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.

Links and Resources

Brownian Motion

Whilst Brownian motion may not be explicitly mentioned on all specifications, it is important to provide some evidence for kinetic theory for students and this contemporary video demonstrates and explains Brownian motion in a fresh and engaging way. Use it to get the idea of invisibly small particles which are molecules established in your students understanding of the topic.

You can also see it with no more than milk, water  and a microscope. Details HERE

publication year
2010 to 2019

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Solids, Liquids and Gases

This is a truly useful set of activities for students of a range of ages. You will want to try out most if not all of them from the simple balance that shows air has mass to the classification of materials exercise, be sure to make it challenging by including materials like jelly, sand and sponge.  The teachers’ notes are also supportive and easy to access regardless of your level of expertise. If you would like more of the same try this link to see how the same resource deals with change of state, the change of volume of water with temperature on page 82 is particularly instructive.

publication year
2010 to 2019

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Mission 3: Space Matters

This wonderful video explains phases of matter in the context of atomic and space physics. Show this to your students to inspire them so that they can see how the different topics in physics are actually linked together.

publication year
2000 - 2009

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Air Pressure

This is a video that shows you how to demonstrate the large forces exerted by atmospheric pressure, definite crowd pleasers for your students. It is engaging and you will want to have a go. There are teachers’ notes included.

publication year
2010 to 2019

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Volume of a Brick

As the concept of density is essentially a mathematical one, this resource is a good way to establish the concept. There are eight math resources here that you can use to practice the calculations and reinforce what density is. Start with the first, letting the students work through the exercise. Then extend their understanding by moving on to the idea of using the known density of water to find the volume of the brick to then find the density of the brick.  

publication year
2010 to 2019

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Under Pressure

Use the movable gauge to measure the pressure of a chosen amount of water then you can vary depth, density and ‘g’ to establish the standard pressure due to a height of fluid equation. Having done that you can go on to explore pressure in different shaped containers.

publication year
2010 to 2019

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