# How does an Anti-tilt chair work?

These chairs are designed as per European Educational Standard Part 1 and 2. These are claimed by the manufacturer as Anti tilt, so basically it makes it relatively difficult for a child to fall when leaning against the back panel. I think angle of back legs play an important role. In a normal chair all the legs are aligned at same angle.

I would like to prove/disprove this claim using laws of physics that it is indeed true.

Any pointers how to go about this proof ?

• -1. Not useful. Any reliable proof must take into account the contortions of the child. Very difficult to calculate using Newtonian Mechanics even when you have all the data. Far easier to test the chair using live subjects. Probably the stability of the chair depends also on its flexibility. Again, not easy to incorporate into a calculation. Commented Sep 22, 2017 at 22:57
• @sammygerbil Thanks for your comment. If it were easy I would have not asked it here. Certain assumptions can be made. I will update my question. Commented Sep 23, 2017 at 3:24

## 2 Answers

In most chairs, the feet are pretty much directly under the corners of the seat. In this chair, the feet are outside the seat. This means the center of gravity of a child will be well inside the rectangle bounded by the feet. This makes a child sitting quietly stable. Even if he sticks his legs out or leans back, his center of gravity will be inside.

If the child rocks or another child bumps the chair, it is still stable because of two more properties.

The chair is low. To tip over, it would have to rotate. Two feet would have to leave the ground. The center of gravity would have to move past the other two feet. This rotation would lift the center of gravity. For a low chair, the lift is larger. It takes energy to lift. It takes a harder bump to tip over a low chair.

The feet are relatively slippery. Certainly, they are not rubber tipped. This means a bump will slide the chair more than rotate it.

For a child to fall back, the center of mass must be further to the back than the point where the chair's back legs touch the floor. Based on the photos, the top of the back is not as far back. The child's center of mass cannot possibly be further to the back than the top of the chair's back. Therefore the chair's are safe. Even if the back is a bit flexible, still the child's center of mass would be nirmally lower and woukd not extend behind the point where the back legs touch the floor. So the chairs look safe enough indeed.