Experiments   1 2

See for yourself how skyscrapers work by trying out these experiments!

Experiment 1a: How a Raft Foundation Works Materials: Soft soil or sand to stand on, for example a thick layer of soil in an old tray, a piece of wood bigger than your shoe What to Do: First stand on one leg on the soil. How far does your foot sink in? Then put the wood on the soil and try again. How far did your foot sink in this time? Did it sink further than the time you did it without the wood? Conclusion: The wood acts like a slab foundation, spreading your weight to reduce the pressure on the ground.

Experiment 1b: How a Raft Foundation Works Materials: A thick stick, a plastic yoghurt pot lid or a round piece of strong cardboard with an approx. 10 cm diameter and some set sand or soil. What to Do: Imagine the stick to be a tall and thin skyscraper, and try to push it into the sand or soil. Now put the plastic lid on the sand and put the end of the stick on the middle of it. Then try to push the stick and its foundation into the sand. Does it still go in so easily? Conclusion: Without the foundation, all the force of your push goes into a relatively small area - the size of the end of the stick. The plastic disc acts like a raft foundation floating on the surface. It spreads the force of your push over a much larger area. So you need to push much harder to make it sink. Engineers can calculate the weight of a building, and work out how heavy the foundations must be.

Experiment 2: Bracing a Frame Materials: Five strips of cardboard, approx. 20 cm long and 2 cm wide, glue What to Do: glue four strips of cardboard end to end to make a square frame. Stand the frame on one edge and push sideways. Does the frame collapse sideways? Now glue the frame and glue another length of cardboard diagonally across the frame. Try pushing sideways again. Does it collapse? Conclusion: A braced frame is much stronger.