This triggered an interesting thought experiment in my head: I wonder if it's possible to be competitive by making the lightest bridge possible that ONLY supports the loading block. Here's a rough analysis:kinghong1970 wrote:i think many teams came in with the impression that their bridge NEEDS to hold 15kg.
my daughters' bridge tests at home started at 5.06g with total load of 3089gr and latest before contest came in at 3.52g which held 2754g
was hoping to break 2k... definitely possible... but alas, event is over for them.
-Last year at Nationals, the 6th place team in Div B got a score of 3288, while the 6th place team in Div C got a 2466.
-The loading block is 5 cm x 5 cm x ~2cm = ~50 cm^3
-Assuming it's made out of Pine, which is common for lumber, the density is ~500 kg / m^3
-Thus the loading block will weigh ~25 g
To place at Nationals, bridges would need to weigh:
Div B: 25 / 3288 = 7.6 mg
Div C: 25 / 2466 = 10.1 mg
So is that even possible? Well:
-the lightest readily available balsa wood has a density of ~70 kg / m^3
-likewise, the smallest cross section you can get is 1/32" x 1/32" (0.8mm x 0.8mm) = 0.64 mm^2
-Thus, this super light and thin balsa will weigh 44.8 ug / mm = 0.448 mg / cm
Using the above weights, and assuming no glue weight, you'd be able to use:
Div B: 7.6 / 0.448 = 16.9 cm
Div C: 10.1 / 0.448 = 22.5 cm
Which in neither case is sufficient length for even a single stick to span the required clear span areas (35cm and 45cm). Just to have 2 bare sticks spanning the gap would require 4 times the length/mass, resulting in 1/4 the score, which in itself wouldn't likely place at virtually any regional competition.
Hence, supporting only the loading block with the lightest possible bridge is NOT a competitive technique by any stretch of the imagination.