On Wed, 19 Jan 2005 13:26:44 -0500, "Glenn Ashmore"
wrote:

I am working on the refrigerator box for the boat. It is top loading and
the lid is to light to press the weather stripping down good. At the same
time I don't want the d*#$ed thing dropping on my head when I am digging in
the bottom of the box to find a lemon for my tequila. So I figured a gas
spring would be a good idea. The problem is how to figure out the closing
force that the spring will give.

The distance between the pivots is 8.5" and the lid pivot will be 1.5" below
the fixed pivot resulting in a downward force when the lid is closed. The
force of the spring is 40 pounds. I vaguely remember that the downward
component of the force is equal to the total force* vertical
distance/horizontal distance) or 40*(1.5/8.5) = 7.058 pounds. Does that
sound correct?

No. That's the tangent, you need the sine.

Now the next question is, for the galley slave's sake, how much force will
it take to start opening the lid? The spring will be pushing down 11" from
the hinge and the lift ring is 18" from the hinge. The lid weighs about 2
pounds and is 20" long.

You left out some details that I'll fill in with assumptions. If the
hinge is at the same elevation as the fixed pivot for the gas spring
and the lid is level when closed, the spring holds the lid shut with
a force of 6.94 lb. The spring is at an angle of -10 degrees,
40*cos(10) = 6.94.

Equating moments about the hinge, the force on the ring to open it
will be 4.38 lb plus 10/18 of 1 lb from lid weight, or 4.93 lb.