Mark Miodownik tests the strength of a concrete beam by walking along it. He discovers that the concrete is not able to tolerate the bending effect his weight is having on it. Compression is seen in the top surface of the beam, and tension is seen in the bottom of the beam, which causes it to fracture.
An animation is used to explain that tiny pores in the concrete expand when stretched, causing cracks to appear and grow.
The clip ends on a challenge. Students could suggest ways to strengthen a beam of concrete, considering the properties of other materials they would add to the concrete and explaining their reasoning. Afterwards, they can research how concrete is reinforced for real in the construction industry. They could draw annotated diagrams demonstrating the difference between concrete and reinforced concrete, and their comparative ability to withstand tension.