When Iffigenia Antoniadou, Outreach lead in Mechanical Engineering, was contacted by Screenhouse Productions, the team behind the BBC Bitesize series, with the question 'Can a 10 year old pull a 10 tonne truck?', our first thought was mini Iron Man suits and genetic modification, but then we got serious and set to work finding a pulley system that would allow just that.
Normally truck pulls are left to the big guns – one of the most famous events at strong-man competitions is the truck pull, where one man will attempt to pull the truck on his own. Competing against our 10 year olds was Britain's biggest gun (and strongest man) Eddie Hall.
Dr Matt Marshall, from the Leonardo Centre in Tribology, worked together with Olivia Manfredi, a student from the Integrated Tribology CDT, to calculate the force needed to pull the truck and source an appropriate pulley system, which they would later restring with abseiling chord to allow a 10 metre pull.
Matt and Olivia calculated that a force of 60–100kgf would be needed to pull the truck. they cross referenced this with a car and the force came out at 20kgf – which fits ergonomic data of the average person being able to push a weight of 25kgf. While they were at it they found that for a 10 year old, the push force is approximately 10–12 kgf, so with the two chosen pulleys (advantage 8:1 and 6:1), the force they needed to generate was in the range of 7.5–12.5kgf. This meant, when you consider a bit of slip and gripping of the rope, it should be achievable for 3–4 children with a little effort.
On the day of filming, Eddie pulled the truck with cheers from the students. Eddie can pull a maximum of 300kg but when the kids had a go; no chance, they were only pulling 30kg between them which meant they needed much more power.
They went to see Olivia who was lifting a massive bag of bricks without breaking a sweat. No, Olivia isn't Super Woman, she was using a crane with pulleys and went on to demonstrate to the children how, with five ropes, it's five times easier to lift the bricks. Olivia explains, "It's just like having a friend to help – if two of us are lifting, the weight is shared between us, we each lift half."
After a bit of experimentation and adaptation, the pulley system was ready and the kids headed back outside to give it another go.
This time, success! Six students managed to pull the truck with no effort at all! Next time I break down on the motorway, forget the RAC, I'm calling these guys for a tow!