this could be interesting

[Equil]

The function you're looking for is probably AddPropImpulse.

Heres the syntax:
AddPropImpulse(string& asName, float afX, float afY, float afZ, string& asCoordSystem);

asName: The prop's name for the impulse to applied to, in this case the chair.

float afX: Impulse applied on the X axis, can be negative of positive values

float afY: Impulse applied on the Y axis, Y axis is always up and down, positive for up, negative for down

float afZ: Same properties as the X axis

asCoordSystem: Co-ordinate system to be used, in this case just use "world"

You'll need to experiment with and use a combination of values to get the right about of impulse you want. If you look in the editor you can see which directions the axises are by the coloured lines:

Red: X axis
Blue: Z axis
Green: Y axis

Hope this helps.