Sophie Abrahams of Oxford Sparks explained why walking backward with your hand in a claw grip over a coffee mug will reduce the inevitable sloshing that leads to accidental spills. This idea was discovered by Korean student Jiwon Han, who proved his thesis with a study he conducted.
Essentially, the natural frequency of a human hand is the same as coffee in a mug. When the hand moves forward, the coffee sloshes in time. Moving backward changes the frequency ratio between coffee and hand, thus limiting the slosh factor.
The natural frequency of coffee in an average size mug is about 4 hertz, that’s 4 sloshes backwards and forwards per second. But the thing is, as you walk the forwards and backwards motion of your hand is also about 4 hertz. …Han suggested walking backwards or the claw grip could be used as ways to avoid spilling coffee. Walking backwards and the claw grip both change the way your body moves. Han proved that both of these methods change the motion of your hand to about 1.7 hertz.
