Question 872623
That's a very strange see-saw, and will not be much fun for that child, but I guess the numbers were chosen to make the arithmetic easier, and I like that.
{{{drawing(300,400,-4.2,1.8,-1.5,6.5,
line(-4.5,-0.866,2,-0.866),
red(line(-3.5,6.062,0.5,-0.866)),
red(circle(0,0,0.1)),
red(line(0,-0.866,0,0)),
locate(-1.75,3.3,red(L-x=8-1=7)),
locate(0.25,-0.16,red(x=1)),
green(arrow(0.5,-0.866,0.5,-1.466)),locate(0.55,-1.07,green(W1=70)),
green(arrow(-3.5,6.062,-3.5,5.462)),locate(-3.85,6,green(W2))
)}}} {{{70*1=W2*7}}}-->{{{70=7W2}}}-->{{{70/7=W2}}}-->{{{highlight(W2=10)}}}
So there you have it. A 10 pound weight at the end of the long arm of that see-saw, will allow that 70 pound child to bounce up and down by about 1 foot. Weee!
{{{drawing(300,400,-4.2,1.8,-1.5,6.5,
line(-4.5,-0.866,2,-0.866),
red(line(-3.5,6.062,0.5,-0.866)),
red(circle(0,0,0.1)),
red(line(0,-0.866,0,0))
)}}} ---> {{{drawing(500,150,-8,2,-1.5,1.5,
line(-8.5,-0.866,2.2,-0.866),
red(line(-6.945,-0.866,0.992,0.124)),
red(circle(0,0,0.1)),
red(line(0,-0.866,0,0)),
blue(arc(0.992,0.398,0.2,0.55,0,360)),
blue(arc(0.992,0.798,0.2,0.2,0,360)),
blue(line(0.992,0.124,0.592,-0.176)),
blue(line(0.592,-0.676,0.592,-0.176)),
blue(line(0.592,-0.676,0.392,-0.676)),
locate(1.1,1.2,blue(WEEE!))
)}}}