A-Level Investigation into Bernoulli Principle

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Hi!

I'm a UK based student undertaking A-Level Physics. I am now in my second year completing my majour investigation. We are allowed to study and investigate any physics phenomina(sp) of our choice, I have decided upon a ball in a jet looking into the effects of Bernoulli.

One of the things stressed by my tutor is that the investigation must provide the opportunity for taking a list of results, varying a factor, and then taking another set of results and looking at the relationship between the two.

I have completed a few initial experiments using some simple apparatus:

• Air Jet
• Boss
• Clamp
• Ping Pong Ball
• Meter Ruler

The Air Jet has four variable jet speeds. It's lowest speed I recorded at 19ms. For the variable in the experiment I decided to change the surface of the ball.

Firstly I used a non-tampered Ping Pong Ball with a smooth surface. The ball gained an average height of 221mm.

Secondly I prepared a Ping Pong Ball dipped into PVA glue and then coated with sand, I believed this would increase the aerodynamic turbulance in the airflow around the ball and therefore cause an increase in the height it gained, I was wrong. The ball again averaged a height close to the non-tampered ball, 218mm.

Thirdly I drilled a series of holes into a ball (3mm in diameter), the holes were spaced randomly. I estimate that around half of the initial surface area of the ball was lost, there were many holes drilled. When I then tried to gain a reading the ball persistantly "fell out" of the air jet and refused to comply with the motion the conventional Ping Pong Ball adopted.

I have a few questions that I hope you can help me with.

1. Can you suggest any other thing I could vary to measure and graph the change in height of the ball?

2. Why does the conventional Ping Pong Ball "hover", that is, maintain a constant height. I'm aware that both the downward and upward forces acting upon the ball must be equal. I believe I can explain this by using either F=ma or P(Momentum)=mv, am I correct?

3. Finally, why does the ball with holes drilled into it fail to be suspended in the air jet?

Any help will be greatly appreciated, thanks for your time.

Matt

 

[Greg Bernhardt]

Hi Matt,

I'm glad to hear you are enjoying your A-Level Physics course. Your investigation sounds like an interesting and fun project to work on.

In answer to your questions:

1. You could try varying the speed of the air jet, or the size of the holes in the ball, to measure and graph the change in height of the ball.

2. You are correct in that the forces acting upon the ball must be equal. To explain this, you can use the equation F=ma, where F is the resultant force, m is the mass of the ball, and a is the acceleration.

3. The ball with holes drilled into it would not be able to maintain the same level of lift as the unaltered ball, because it has less surface area for the air jet to push against. This results in the ball not being able to stay suspended in the air jet.

I hope this helps. Good luck with your investigation!