Ridgefield — How much weight can a 9-ounce bridge built of balsa wood and popsicle sticks handle? Over 400 pounds, as it turns out — if it’s built just so. That was the finding of the Ridgefield High School physics class that studied problems of “elasticity, compression, tension and scaling,” according to teacher Janie Call, while designing high-strength bridges. Also assembling bridges were students in the Highly Capable Program at South Ridge Elementary School and Union Ridge Elementary School. Others involved were Tevis Laspa, a community volunteer who started the project three years ago, civil engineer Justin Clary and architect Casey Wyckoff, who judged bridge aesthetics.