Education
Air Pressure Levitator
What happens?
These three separate exhibits all illustrate the Bernouilli Effect.
1. Press the green button to start the airflow. Hold the red disc with its flat side up. Lift it slowly up underneath the clear plate. Air is directed downwards onto the red disc as you lift it towards the source of the air. What do you feel as it approaches the clear plate? At first, the airflow presses the disc downward. But when the disc is close to the clear plate, you can feel it being lifted from your hand towards the source of the airflow.
2. Press the green button to start the airflow, and point the nozzle between the two loosely suspended [table tennis / plastic] balls. What happens to them? You might expect the air to push the balls apart. Instead, it makes them cling together as the balls are attracted into the airflow.
3. Press the button to start the blower. Put a ball into the stream of air. The ball should stay trapped in the air stream. How far can you tilt the nozzle before the ball falls off? Can you pass the ball through the hoop?
How does it work?
These three exhibits illustrate the Bernoulli Principle which states that, as the speed of flow of a fluid increases, the pressure exerted in that fluid decreases. The word fluid means anything that flows, and includes both liquids and gases. In these exhibits the fluid is air.
1. The pressure in the moving air from the pipe is less than in the still air under the plate. When the air hits the plate it accelerates outward, and its pressure drops further. This air exerts less pressure on the top of the plate than does the still air in the room underneath. The resultant still air force pushes the plate towards the air pipe and holds it up against the downward force of gravity.
2. The pressure in the moving air between the balls is less than in the surrounding still air. This moving air exerts less pressure on the inner surfaces of the balls than does the still air on their outer surfaces. The resultant force due to the greater pressure of the still air pushes the balls together.
3. As the air flows around the ball, it speeds up and the pressure near its surface decreases. If the ball is not in the middle of the air stream, the pressure variations always push the ball back towards the middle of the stream.
Why is it important?
Application of the Bernouilli Principle illustrated here is essential in two areas: air transport and in pumps. Its use in aircraft design is illustrated in several local exhibits. The 'Lift' exhibit shows how it can be used in a pump. The moving air flowing across the top of the tube is at a lower pressure than the air inside the tube, so the air inside is sucked out.
How does it relate to the primary curriculum?
- Curriculum objectives: Mutual understanding (if working in a pair or small group)
- Cross-curricular skills: Communication (if working in a pair or small group)
- Thinking skills and personal capabilities: Thinking, problem solving, decision making; Working with others (if working in a pair or small group); Self-management
- Area of learning - The world around us: Pupils can explore the causes and effects of movement, forces and energy
- Learning experiences: Investigating and problem solving; Active and hands on; Offers choice; Challenging and engaging; Enquiry based
- Attitudes and dispositions: Openness to new ideas; Curiosity
How does it relate to the post-primary curriculum?
- Science: Pupils should have opportunities to: develop their manipulative skills; develop their skills of investigation and scientific enquiry to explore forces and energy transfer
Thinking skills
Paying attention to the situation; Asking appropriate questions; Identifying factors in the situation; Generalising: using experiment and inductive reasoning; Analysing elements of the situation
Learning styles
Visual; Kinaesthetic; Spatial
Where can you find out more?
http://home.earthlink.net/~mmc1919/venturi.html (Bernoulli animation)