What makes the bridges so strong
Oh, Hi guys.
Scrips and I were just playing with some blocks
You know, it may not seem like it,
but the cities in towns that we live in
are all built using the same rules
as a little pertain village over here
She said ” the real ones are bigger”
and one of viewer Hanna from the UK
want to know how somethings that we built still stay standing
so she sent us a really great question
why are bridges so strong?
Sometimes when a road or a railroad truck needs to go across something big
like a river or a deep valley
experts called engineers design and build bridges to do that job.
and bridges can be really busy
例如 我们说的 世界上最繁忙的桥
take for example, what is said to be the world’s busiest bridge,
the George Washington Bridge in New York City.
Look at all those cars and trucks
It has to be pretty sturdy to carry so many people and cars.
For bridge carrying that much weight
It has been built special material like iron and steel.
but it takes more than tough materials to make a strong bridge.
So let’s look at how bridges work.
One very simple kind of bridge is called a beam bridge.
When we say simple, we really do mean simple.
A beam bridge can be just a log that used to walk across the stream
or put a long ship of a carboard between two short blocks
That’s a beam bridge too.
All bridges can hold a certain amount of weight
for what happens if we put too much weight on the beam bridge.
Let’s find out.
so bridge that carries trucks and cars which are very heavy
would have to be stronger
that the bridge carries by people on foot
So how do we make stronger bridges?
While overtime people have learnt that a certain shapes can be used to make stronger bridges.
Take a look at this railroad bridge
It has to be strong because it carries trains.
What shape do you see?
That’s right, triangles
and that’s not by accident
The fact is triangles are really strong shapes for building
If you put force on one side of a triangle it bends.
But if you put force on its point
it keeps the shape.
That’s because the two sides of the triangle are pushed down by the force
and the bottom get stretched out to both sides.
Each side feels the force but none of them bends.
And this makes the triangle a really sturdy and stable shape.
This is why you’ll see lots of triangles in bridges.
both above of the part you actually travel along called the deck and below it The length showing a triangle that you see
in a bridge is called the truss
Truss is how the bridge spread out of the way that has to carry
But, now all bridges are made of trusses
If a bridge has to cross a really wide body of water
it might be too difficult or expensive to built a truss bridge
So engineers designed another kind of bridge called the suspension bridge
The Golden Gate Bridge in California is a great example of a suspension bridge
Suspension bridges work by using a force called tension
tension is just pulling something tight
Suspension bridges are made of a deck that’s hung or suspended
from one side of the bridge to the other
These cables are suport by tall towers
and neither how down telly or anchored on both ends
Suspension bridges are strong because of the force on the bridge gets spread out
来来往往的汽车 以及 满载的列车 其重量
The weight of the cars and trends of horses whatever is travelling aross it
pulls on the cables creating tension
Those cables that pull down of the towers
also pull on anchors on either end of the bridge to hold up the deck
I can go on it about all kinds of clever bridges
但是 桥梁的坚固性不仅仅是 使用了坚实的材料
But, basiclly bridges are strong not only because tney are made strong with materials
but also because of the smart designs dreamed up and planned by engineers
So things were asking Hanna and thank you for Hanna are within us social kids
see you next guy