from the try-this-at-home dept.
Submitted via IRC for Bytram
A group of first year students at Roskilde University, supervised by Dr Tina Hecksher, have shown that water-filled balloons behave very similarly to tiny water droplets, by bouncing them on a bed of nails.
Their work, published today in the European Journal of Physics in collaboration with Professor Julia Yeomans at Oxford University, was inspired by one of Professor Yeomans' previous papers studying water droplets bouncing on hydrophobic surfaces patterned with lattices of submillimetre-scale posts.
Dr Hecksher said: "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.
"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."
The study 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 under the board to log the impact force, the team measured impacts at different velocities and the balloons' resulting behaviour.