Why arches are strong

In the picture

1. 1Keystone at the top of the arch: where the load presses down
2. 2Force flowing along the curve: the weight is passed sideways and downward
3. 3Abutment: the solid support that takes the push at the end of the arch
4. 4Curved violin top: a thin curved plate that carries a load by the same route
5. 5Flat board: the load bends it in the middle and it sags

Examples

• Stone bridges and Roman aqueducts carry heavy traffic and water on arches.
• An egg shell resists a squeeze on its ends because its curve spreads the force.

Quiz: Why arches are strong (Age 12)

1. 1

   A heavy weight presses down on the top of an arch. What happens to that push?

   • It stays at the top and crushes the stone there.
   • It bounces back up and pushes against the weight.
   • It is passed along the curve, sideways and down, to the supports.
2. 2

   Why does a flat board collapse under a load that an arch can carry?

   • It has no curve to share the load, so it bends in the middle and breaks.
   • It is always made of weaker material than an arch.
   • It sends all the weight sideways, so its ends snap off.
3. 3

   What job do the solid supports at the ends of an arch do?

   • They take the sideways push that comes along the curve.
   • They keep the arch from bending in the middle.
   • They hold the top stone in place.

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.