Can water balloons bounce off from bed of nails?

A new study finds that water-filled balloons behave very similar to tiny water droplets, by bouncing them on a bed of nails.

Researchers from Roskilde University in the Denmark explained that water-filled balloons began to retract in the air rather than on the surface because some of the material penetrates into the nail pattern, recoils and -- if the impact velocity is high enough -- lifts the balloon off the bed of nails before it has time to retract.

The findings were published in the journal of Physics.

"We wanted to know if the so-called 'pancake bounce' effect - where the droplet lifts off the surface at its maximal extension - which was observed in the microscopic experiments could be replicated on a macroscopic scale," said study author Dr Tina Hecksher.

"Scaling up the experiment allowed us to measure the impact forces in the pancake bounce, which gave a deeper insight into its dynamics. It also provides a really useful teaching tool to demonstrate to students in a very cost-effective, straightforward and eye-catching way how

these forces work," Dr Hecksher added.

They compared the impact of the balloons - taking the place of water droplets - landing on a flat surface and on a bed of nails - modelling the submillimetre posts.

Using large store-bought party balloons, a digital reflex camera running at 300 frames per second to record the impact in slow motion and a piezoelectric sensor -- to measure changes in pressure, acceleration, temperature, strain, or force by converting them to an electrical charge-- under the board to log the impact force.

The team measured impacts at different velocities and the balloons' resulting behaviour.

The study indicated that on the bed of nails, the balloon actually made a pancake bounce: it lifted off the bed of nails at its maximum deformation and began to retract in the air rather than on the surface.

"The behaviour of the balloons is surprisingly similar to that of millimetric bouncing drops. In particular, the pancake bouncing effect was reproduced showing the same reduction in contact time as in the microscopic experiment, but with absolute timescales longer by a factor more than 10. And the transition from normal bouncing to pancake bouncing happens at comparable impact parameters," Dr Hecksher explained.