Liz Bonnin, Dallas Campbell and Jem Stansfield take on more scientific challenges. Engineer Jem becomes a crash test dummy to discover how much g-force his body can take, while scientist Liz gets the Olympic treatment for Sport Relief. Dallas enters the weird world of the atom, and roving reporter Dr Yan Wong dives into a shark tank to explain why there are no long snorkels.

• Dallas Campbell
• Liz Bonnin
• Jem Stansfield