# Pneumatics (Behavior of Gases under Pressure)

#### Students’ Learning Outcomes

·         Explain how gases behave under pressure.
·         Describe the causes of gas pressure in a container.
·         Identify the application of gas pressure.
·         Describe the term atmospheric pressure.

#### Information for Teacher

·         A gas is the most complex and difficult to understand state of matter.
·         A gas has these three main properties:
1.       Doesn’t have any definite shape.
2.       Doesn’t have a definite mass.
3.       Doesn’t have a definite volume.
·         Gas pressure: pressure is created by the force of gas particles running into a surface.
·         There are three states of matter e.g. solid, liquid, and gas. Every state made up of atoms, molecules, which are always in random motion. These molecules exert a force on the walls of the vessel.
·         The collision of gas particles with the walls of a container and with themselves is called gas pressure in a container.
·         “Pneumatics” is the term which is used for gas molecules in pressure.
·         Pneumatics machines are driven by the pressure of gases, usually air. Unlike liquid, air can be compressed into a smaller space, and this increases its pressure.
·         Gas pressure is one of the most important ways of making machines to move, e.g. the working of a steam engine, fire extinguisher and aerosol sprays.
·         Atmosphere is a wide ocean of air. It is blanket of gases that surrounds the Earth.
·         Air exerts pressure on our body.
·         The pressure on the Earth caused by the weight of the gases in the atmosphere is called atmospheric pressure.
·         The closer you get to the ground, the greater the atmospheric pressure.
·         The pressure of air molecules at ground level or at plain surfaces is greater than the surfaces of hilly areas.
·         Air insider a ball/tire pushes out in all directions keeping it blown up.
·         Barometers and manometers are the instruments to measure pressure of a gas with respect to its surroundings.
·         Atmospheric pressure is defined as the force per unit area exerted against a surface by the weight of the air above that surface
·         Atmospheric pressure is measured in mile bars (m b).
Atmospheric Pressure

#### Material / Resources

Charts showing different aerosol sprays, juices, straws, syringes, corks, rubber tube, balloons, aerosol sprays

#### Worm up activity

·         Ask some questions to assess the previous knowledge of the students.
Q1. What is surrounding the earth?
(Expected response: Atmosphere)
Q2: what is atmosphere?
(Expected response: Atmosphere is a cover or blanket of different gases)

#### Activity

·         Do the following activity to give the concept of atmospheric pressure as:
o   Call one of the students and give him a pack of juice with straw.
o   Tell him/her to drink the juice with the straw.
o   The juice in pack will start to move upward as he/she sucks the juice.
·         Tell the student that when we drink juice or bottle, we suck the air from the juice pack or bottle and thus a vacuum is created in it. The outside pressure of air become greater from the inside pressure and this greater pressure crushes the juice pack by pushing the liquid up into the mouth.
·         Tell students about the working of the cane crushing activity which works due to the difference of atmospheric pressure.
·         When the atmospheric pressure outside the cane is much greater than the pressure inside the cane it crushes the cane and makes its volume very small.

#### Activity 1

·         Instruct the students to take two syringes and take out their needles and put a cork at the opening ends.
·         Move the plunger inward, then a stage will come when plungers will no more move inward, because the air molecules are now more crowded and cane not be pressed further. In this way a high pressure is produced in the syringe which stops the downward movement of the plunger.

#### Activity 2

·         Show a chart of aerosol spray:
·         Tell the students to spray out from the aerosols.
·         The students will that an air is coming out from the spray. But when they shake the bottle they will feel that there is some liquid in it. Tell students about the working of aerosol.
·         The aerosol has some empty space above the liquid where the gas is enclosed.
·         When bottle is shaking gas mixes with liquid and produces a high pressure.
·         When the valve is opened by pressing the button, the high pressure gas liquid mixture inside the bottle comes outside where the pressure is low.
·         In this way the expanding gas forces the liquid out of the nozzle.

#### Sum up / Conclusion

·         Gas pressure: pressure is created by the force of gas particles running into a surface
·         “Pneumatics” is the term which is used for gas molecules in pressure.
·         A foam and water fire extinguisher is pneumatic machine which uses compressed carbon dioxide gas.

#### Assessment

·         What happen in the pressure cooker on heating?
(Expected response: Pressure inside the pressure cooker increase than the outside atmospheric pressure)
·         What units for atmospheric pressure are used in weather for forecasting?
(Expected response: mill bars 1 bar =100 k P a = normal atmospheric pressure/ 1 bar = 1000 mill bars)
·         Why food takes more time to be cooked on hilly areas?
(Expected response: Due to low pressure in hilly areas)
·         Why do you think air is used rather than water in tires?
(Expected response: because air more compressible than water)
·         In which direction gas particles will move when they are heated?
(Expected response: They will move in upward direction)