Sweet spot or centre of percussion? Or both? For those unfamiliar with tennis, golf, cricket or physics, these terms refer to that point on the club, racquet or bat where it is possible to hit the ball without feeling reverberations and which sends the ball flying at the fastest speed.
In a lecture-demonstration on sport and science, Dr Brian Delf of the Cardiff science centre, Techniquest, sought to give teachers some practical pointers on how to demonstrate scientific principles through sport.
Dr Delf showed how pupils can easily see a frisbee's centre of equilibrium, as it balances on a finger placed at the centre, but it is harder to balance a golf club vertically, and when it falls, the club rotates.
For a person walking a tightrope, "very nice physics is going on", said Dr Delf as a volunteer struggled on a balancing beam. The centre of equilibrium changes all the time, as he tries to stop himself from rotating to the ground.
Any sporting situation contains basic bits of physics, Dr Delf said. But he added sadly, these principles won't make you play better.