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Types of structures: triangular and suspension bridges

0:01crown don't
0:13all hi guys we never display with some blocks
0:16you know it may not seem like it but the city is in town that we live in
0:20are all built using the same rules at their little pretend millage over here
0:23it's just got the real ones are bigger and one of our viewers six-year-old
0:27Hannah from the UK
0:28want to know how so many things that we build stay standing
0:31so she sent a really great question why our bridges so strong
0:35actually question sometimes when I wrote our railroad track needs to go across
0:39something big like a river or a deep valley
0:42experts called engineers design and build bridges
0:45to do that job and bridges can be really busy take for example
0:49what's said to be the world's busiest bridge the George Washington Bridge
0:52in New York City look all those cars and trucks
0:55it have to be pretty sturdy to carry so many people in cars
0:59for bridge to carry that much weight happy build a special material like iron
1:03and steel
1:03but it takes more than tough material to make a strong bridge so let's look at
1:07how bridges work
1:08one very simple kinda bridge is called a beam bridge
1:11when we say simple we really do mean simple a beam bridge can be just
1:15a log they used to walk across the street or put a long should have
1:19cardboard between two short blocks
1:21that the beam bridge to already can hold a certain amount of weight but what
1:25if we put too much weight on a beam bridge let's find out
1:33it collapses
1:34so great that carries trucks and cars which are very happy
1:37will have to be stronger in a bridge that carries bikes are people on foot
1:41which are lighter so how do we make stronger bridges well over time people
1:45have learned that certain shapes can be used to make stronger bridges
1:48take a look at this railroad bridge it has to be strong because it carries
1:52what shape do you see that's right triangles and that not by accident
1:56the fact is triangles are really strong shapes for building if you put or
2:00someone find a triangle
2:01it bent but if you put forth on that point it keeps its shape
2:05that's because the two sides of the triangle are pushed down by the force
2:09and a bottom gets stretched out to both sides each side
2:12feel the force but none of them patents and this makes the triangle a really
2:16and stable shape this is why you'll see lots a triangle the bridges
2:20both above the part that you actually travel on call the deck and below it
2:24launching a triangle that you see in a break is called the Trust's trusses help
2:28spread out the weight that I have to carry but not all bridges are made of
2:31ever bridge across a really wide body water it might be too difficult
2:35or expensive to build a truss bridge so engineers design another kind a bridge
2:40call the suspension bridge
2:41the Golden Gate Bridge in California it's a great example up a suspension
2:45suspension bridges work by using a force called tension
2:48tension it just pulling something tight suspension bridges are made up in Dec
2:52that hung or suspended from the cable that stretch from one side of the bridge
2:57to the other
2:57these cables are supported by tall towers and then are held on tightly
3:01or anchored on both ends suspension bridges are strong because the force on
3:05the bridge gets spread out
3:06the way to the cars are trained to horses whatever's traveling across it
3:10polls on the cables creating tension those cables then pulled down the towers
3:14also pull on acres on either enter the bridge to hold up the deck
3:17I cannot on and on about all kinda clever bridges but basically
3:21bridges are strong not only because they're made a strong materials but also
3:24because the smart designs dreamed up
3:26and planned by engineers something gravity and that and thank you for
3:29hanging out with that fight you can't
3:31the NFL
3:32 and are

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