5-SLG-3

Outcomes

• Pupils can describe Brownian motion
• Pupils can convert °C and K

Specification References

• 5.9 understand the significance of Brownian motion, as supporting evidence for particle theory
• 5.10 understand that molecules in a gas have a random motion and that they exert a force and hence a pressure on the walls of the container
• 5.11 understand why there is an absolute zero of temperature which is –273°C
• 5.12 describe the Kelvin scale of temperature and be able to convert between the Kelvin and Celsius scales

Starter

Demo Brownian motion (microscope) and here's an animation which shows what's going on.

Main Body of Lesson

Use the mechanical model for Brownian motion model gas particle behaviour: Piston moves up due to increase in pressure of gas caused by increase in temp. Pressure caused by molecules hitting the sides of the container, changing momentum and exerting a force on the side. 1. Faster molecule – bigger force. Press = F/A so bigger Pressure. 2. Faster molecules leads to more frequent collisions with sides – higher pressure. Try to avoid shouting over the model (it's quite loud). Stop it periodically and discuss the changes that occur as you change the speed of the piston. There is a worksheet in the shared folder (Gas molecules and pressure) exploring these ideas.

Pupils need to be able to explain pressure by talking about the gas particles colliding with the walls of the container, exerting a force over a given area.

Another approach here is to use role play so that the pupils model what the particles are doing in solids, liquids and gases before moving onto Brownian motion (see Brownian motion role play in shared).

To introduce the Kelvin scale you could start by calibrating ungraduated thermometers using ice and boiling water. These can then be used to measure the temperature of another liquid (teacher's coffee for example). You could even ask them to put 273 and 373 as their reference temperatures and then divide up the gap between into 9 segments (each representing 10K). After this introduce the conversion calculation and try a few examples. Make clear that the Kelvin scale is an absolute scale so starts at 0 and that no negative values are possible. Pupils also need to know that the particles wouldn't be moving at absolute zero. There is a worksheet to practice these calculations in the shared folder.

Plenary

Have a series of conversions for pupils to do on mini whiteboards.

Homework

Can use the sheets mentioned if you haven't used them already. Also pg 100-101 in the textbook.

Additional Information

Resources Required

• Brownian motion smoke cell and mechanical model
• Alcohol thermometers with no markings
• Ice
• Beakers and glass flasks
• Teacher’s cup of tea/coffee - thermometer or SPARK with temp. probe