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An investigation into what makes a comfortable chair by changing the net force exerted on a seat and observing the change in pressure. The presenter talks to an ergonomist about seat comfort. First they measure the up and down force when sitting in different chairs. They then plot the pressure profile across the area of the presenter's bottom when sitting in a car seat. They find that there are high pressure points and then repeat the test with a slightly different seating position, in which the upper body leans back and the legs are stretched out. This evens out the pressure on the sitter.
This clip is from:
First broadcast:
17 May 2007

Classroom Ideas

Ask students to estimate the pressure they exert on their chairs in the classroom. As a home exercise, students could estimate the pressure exerted as they lay on their beds. Compare results with the class. Discuss with students the difference between mass and weight, and between force and pressure. Consider a bed of nails as an example where the spread of force allows someone to lie down without being harmed.