7G Solids, Liquids and Gases

Lesson 3: Pressure

Learning objectives

  • To apply a model to new phenomena to explain behaviour
  • That gas particles are moving around all the time
  • That gas pressure is caused by particles hitting the walls of the container

Learning outcomes

  • To explain their observations in terms of particle theory
  • Describe gas particles as moving all the time and pushing against surfaces
  • Explain that the can collapses because there are fewer air particles on the inside pushing out than o the outside pushing in.

Resources

Worksheets – “Cans”, “Pressure”. Differentiated worksheet “pressure” – missing words version.

Demonstration – collapsing can – suction pump and plastic can.

OHT – first column of “Pressure” worksheet for guided writing activity

Class practical – empty drinks cans, troughs, clamps, Bunsen burners, tripods and gauzes.

Lesson Outline

  1. Starter. Pupils add particles to worksheet “can” diagrams; one can filled with water, the other “empty”.
  2. What is pressure? Describe how particles collide with the container and cause pressure. The “empty” can retains its shape because the pressure inside the can is the same as the pressure outside the can.
  3. On the board - draw the following boxes of particles and pose the questions:

A B

Where is the pressure the

highest? Why?

C D

Where is the pressure the

highest? Why?

  1. Demonstration – collapsing can. Use pump to suck air out of a plastic can.
  2. Guided writing activity. – Worksheet “Pressure”. [a missing words version is available for very weak pupils]. Begin b using OHT to discuss the first column of the sheet that has been completed already. Show how appropriate particle drawings can be added and how the three sentences can be constructed, perhaps revealing one sentence at a time. Pupils then complete the next two columns (leave the final column for homework).
  3. 6. Class practical. Collapsing tins. Pupils place a tiny amount of water in the bottom of a drinks can and then place on a tripod and heat over the Bunsen flame. Once steam is coming out of the hole in the top of the can they use the clamps to quickly invert the can and dunk it into the cold water trough.
  4. Plenary: question – why did this happen?

Homework: the final column of the pressure worksheet allows for formative assessment of the drawings and descriptions.