Spider webs are strong in the sense thatthey're strong for their extremely smallthickness. A strand of a spider web (calledspider silk) is very thin, so we can easily breakit, but if we could weave many strands together toa thickness of a climbing rope, thisspider-web-rope would be many times stronger thanthe rope, even stronger than some types of steel.For comparison, the tensile strength (how muchpulling force along the length of something youcan apply before it breaks) of some steels arearound 400 to 800 megapascals while silk fromsome spiders can have tensile strength of 1,000megapascals. However, it is very difficult toget enough spider silk to make a thicker cable,and we do not yet have a way to use spider silkfor practical purposes.
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It is important to think about how much spider websilk you are dealing with when you break through ausual spider web. Its a really really smallamount, right? But what if you had a largeamount of web? Or a web with strands that were aninch thick? This is why engineers describematerials with "absolute strength", whichdescribes a material's ability to resistbreaking regardless of how much you have of it.
Spider silk actually has strength that ispretty close to steel, but spider silk is alsomuch less dense (density = weight of somethingper volume of that something). So if you hadtwo ropes of equal weights, one made of spiderweb and one made of steel, the spider web ropewould actually be five times stronger than thesteel rope!
Hope that helps!spider web has an extremely high"strength-to-weight ratio", that is, theamount of weight that a spider web can hold upwithout breaking is huge compared to the weight ofthe web itself. However, an animal the size of aspider can only hold so much web material in itsbody, so the total amount of weight that aspider's web can hold up is very small compared tothe amount of weight that, say, your body can holdup.
It's the same principle of how a table built outof toothpicks for legs wouldn't be able to hold upmuch weight compared to a proper table. Thetoothpicks are just too small.
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The key to this is the definition of"strength". When someone uses the wordstrength, they typically mean the amount of weightthat can be lifted, or the amount of force thatcan be supported. By this interpretation, spiderwebs don't seem all that strong; they can bebrushed aside with only a very small force.However, in scientific contexts (such as inreporting strengths of materials, like spidersilk) strength is force per area supportingthat force. When we consider that spider silkhas a diameter around 0.003 mm (roughly 10 timessmaller than human hair), we can see that even asmall force will give a very large strength. Infact,in terms of force per area, the strengthof spider silk is greater than that of many typesof steel.
Pieces of steel tend to be much larger thanpieces of spider silk though, so steel seemsstronger because it is easy to consider only theforce (and not the force per area) taken to breaka piece of steel. A discussion of the structure ofspider silk which leads to this strength can befound in previous ScienceLine answers.
This is a really interesting question becausepeople always mention that the silk that makes aspider’s web is roughly as strong as steel. Ifthat is true, how come we can break it soeasily? The truth is that spider’s silk isvery strong but there just is not very much of itin a web. In fact, an average strand in a web isonly one tenth the width of a human hair. Sincethere is so little silk it is easy for us to breakit in the same way that it is easy to snap a twigin half but not a tree. If we had enough spidersilk it would be as strong as a steel beam whileweighing significantly less. Thank you foryour question!
A spider’s silk is around 3 micrometers (0.003millimeters) in diameter, so it is very thin. Itis useful to think of a rope made of many threadsas an analogy. A single thread could never hold upa person, but by intertwining many threads into arope, it can easily support the weight of a human.
When we say how strong something is, weusually mean its tensile strength, whichmeasures how much stress a material can withstandbefore breaking. A single strand of spider silk isstrong for its size and can withstand the force ofan insect that flies into it. If we could somehowscale up the spider silk to be 100 times thicker(0.3 millimeters) by constructing a rope of spidersilk, it would have a strength comparable a 22gauge steel wire.
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