Balloon balance

Another fascinating way to demonstrate the Bernoulli Effect requires only a hairdryer and a balloon. When the hairdryer is directed upwards and switched on it creates a stream of moving air; a balloon can be “balanced” in the airstream (Figure 6a). Ask your pupils to predict whether a small balloon would float higher or lower than a larger one. It is possible to have two balloons of different sizes balanced in the airflow at the same time, which demonstrates neatly that the larger balloon floats higher.

Figure 6a - Two balloons in airstream

If the angle of the hairdryer is altered (Figure 6b), the balloon will move to stay in the centre of the airstream. The air in the centre of the air stream will be moving a little faster than the air towards the edge.

Figure 6b - One balloon in airstream

This is due to the fact that the air at the sides rubs on the stationary air in the room and is slowed a little. If the balloon begins to drift off centre, the faster air passing the balloon will be on the side towards the centre of the stream, with lower pressure, and the balloon will re-align itself.

Another balloon balance

How many children could stand on a board supported by four balloons?

Children will know that if they stand on a balloon it will burst. However, if a board is placed over four balloons, it will take the weight of four children without the balloons bursting. This is best done with the balloons taped to an upturned table to restrain them, and the table legs can provide support for the volunteers.

Figure 7 - Two 'children' in SSERC put the balloons under severe pressure!

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