# Impact Force after falling of a chair

1. Nov 21, 2008

### Steve Smith

Hi,

Hopefully somewone will know the calculation to find out the impact force for one person sitting on a chair and falling backwards with a full deaceleraton to a hard floor, what would the impact force be to the base of he head when stricking the floor.

Chair is a chair with a bottom and a back rest section
From floor to bottom of chair 360 mm
Whilst in the sitting position head from floor 1100 mm
Weight of person on the chair 100 kg

The chair flips backwards and the person goes backwards sitting on the chair and head strikes the floor, what would the impact force to the persons back of the head be ???

Regards,
Steve Smith

2. Nov 21, 2008

### mgb_phys

This is very hard to calculate, you can get the speed they hit the floor with fairly easily.
But the force will depend on how their head slows down as it hits (f=ma where 'a' is the deceleration)
It's even more complicated for a head, the skull will slow at a certain rate but the brain will slow down at a different rate as different structures absorb energy in different ways.

3. Nov 21, 2008

### Steve Smith

Hi,

I agree with your statment to mesure the aceleration one problem I believe in the calculation is that the movement of the fall is dot directly downward but a slight pendulum affect as tha chair tilts over the head is not making a direct fall from 1100 mm but swinging at a pendulum that is why i mention the chairs dimensions.

The deacelaretion would be 0 mm hitting a concreted or tiled floor as no movement could still occur after the impact.

Yes the brain momentum and force would be diffrent due to t own density / mass / weight and the liquid between the brain and scull.

Just wanting the calculation based on the imact force to the floor but not as a 100% downward fall but a pendulum fall due to the chair dimensions.