AIR, ITS PROPERTIES & BEHAVIOUR

Before we investigate how aeroplanes fly we need to look at the properties and behaviour of the air through which they move. Air is a mixture of gases, 78% Nitrogen, 21% Oxygen with small amounts of water vapour, carbon dioxide, argon and other Nobel gases.

Although the Earth’s atmosphere extends above its surface to an altitude of approximately 120 km most of its atmosphere is found in a layer called the Troposphere that extends to an altitude of about 11km.

If the average pressure exerted by the Earth’s atmosphere is 101325 Pascals (N/m2) at sea level, what is the weight of the air above us equal to?

Fluids

Gases and liquids consist of particles (molecules) that can freely move past one another and have the tendency to assume the shape of the container they occupy. Substances that exhibit these properties are said to be fluids.

In the next few experiments you will be looking at the behaviour of fluids as they move over the surface of other objects, and the effect that this movement has on the objects themselves.

Fluid Flow & Pressure Effects – Experiment 1Purpose: To investigate the behaviour of air as it moves over an object and the effect that

this movement has on the object.

What You Need: 1 sheet A4 paper, scissors.

1 desert or teaspoon.

What To Do: Part A. From the A4 sheet cut a strip that is 5 cm wide and 25 cm long. Hold one end just underneath your bottom lip and blow across the top of the strip.

Part B. Gently hold a teaspoon vertically by the tip of its handle and place its convex side into a stream of water from the tap.

(A) (B)

Prediction A

What do you think will happen to the paper when you blow across the top of it?

Observation A

Prediction B

What do you think will to the spoon when it is placed into the stream of water?

Observation B

Explanation(s): Diagram

Conclusion:

Fluid Flow & Pressure Effects – Experiment 2

Purpose: To investigate the behaviour of air as it moves over an object and the effect that this movement has on the object.

What You Need: 2 full water bottles, retort stand and clamps and cotton thread.

What To Do: Suspend the two water bottles so that they hang and are separated by about 2-3 cm as shown in the diagram. Blow a steady stream of air between them.

Prediction: What do you think will happen to the bottles when you blow between them?

Observation(s):

Explanation: Diagram

Conclusion(s):

Fluid Flow & Pressure Effects – Experiment 3

Purpose: To investigate the behaviour of air as it moves over an object and the effect that this movement has on the object.

What You Need:1 polystyrene ball, 1 beach ball, 1 air blower.

What To Do & Results:If you are using a vacuum cleaner for this experiment you will need to ensure that it is blowing air out, not sucking it in. Ask an adult to help you do this.

Hold the nozzle so that it is pointing straight up into the air and turn it on.

Prediction(s): What do you think will happen when you place the polystyrene ball into the air stream?

What do you think would happen to the ball if you gently tilted the air stream until it was at an angle of about 20o – 30o from the vertical?

Observation(s): (As part of your answer draw a diagram showing what happened)

Explanation:

Return the air stream to the vertical and allow the polystyrene ball to stabilise.

Prediction: What do you think will happen to the ball when you gently try and push it out of the air stream? Try it!

Observation:

Explanation:

Repeat this experiment for the balloon and beach ball. Which ball performed the best? Can you offer any suggestions as to why?

Conclusion: In terms of air movement around the ball try and explain your observations. You may find it useful to include a labelled diagram as part of your answer.

Fluid Flow & Pressure Effects – Experiment 4

Purpose: To investigate the behaviour of air as it moves through a confined space and the effect that this has on the object making the confined space.

What You Need: 1 sheet A4 paper, sticky tape, scissors and ruler.

What To Do: From the A4 sheet cut a strip that each measures 8 cm x 21 cm. Make the paper bridge as shown in the diagram and tape it to the desk.

Diagram of Observations

PredictionWhat do you think will happen to the paper when you blow through the tunnel?

Observations:

Explanation:

Conclusion:

Which answer, a), b) or c) is correct? Based on your observations to the above experiment explain your answer.

Whose principle is this?

Fluid Flow & Pressure Effects – Experiment 5

Purpose: To investigate the effect that air moving over an aerofoil has on the wing.

What You Need: The equipment shown in the diagram will be set up for you. The shape of the model wing is called an aerofoil.

Prediction: What do you think will happen to the wing when air from a fan is directed towards it?

What To Do: Use a fan to blow a stream of air towards the model wing.

Observation:

Explanation:

Fan!

Conclusion: In terms of the lift produced try and explain your observations. You include a labelled diagram that shows how the air moves over the aerofoil and the forces acting as part of your answer.