How To Build a Strong Wall - By MITK12Videos
Transcript
| 00:13 | Hello . I'm Peter . Let's go on a journey | |
| 00:15 | and learn about materials together . Today , we will | |
| 00:18 | show you how you can mix materials to improve the | |
| 00:21 | strength of a mortar wall . This is jenny , | |
| 00:24 | she is mixing mortar . You can make a simple | |
| 00:27 | mortar or concrete out of a mixture of sand and | |
| 00:29 | clay . But of course you also need to add | |
| 00:32 | water . Here we take a piece of the mortar | |
| 00:34 | and hang a bucket from it . Then we increase | |
| 00:37 | the weight of the bucket . Step by step by | |
| 00:39 | adding little metal weights that didn't work so well . | |
| 00:45 | If we slow it down , we can see the | |
| 00:47 | cracks forming . Let's explore how we can make it | |
| 00:51 | better . There are a ton of different materials that | |
| 00:54 | show quite different behaviors when you pull on them . | |
| 00:58 | If we take false a would a very bendy kind | |
| 01:01 | of wood , It doesn't break so easily when jenny | |
| 01:03 | pulls on it and when jenny stops pulling it goes | |
| 01:06 | right back into its original shape . We can also | |
| 01:10 | look at another material you have probably seen before . | |
| 01:13 | Metal window screen . The metal does not break easily | |
| 01:16 | at all . Rather , it changes its shape and | |
| 01:18 | does not change back when jenny stops pulling on it | |
| 01:22 | . Now you can see the mortar wood and the | |
| 01:25 | window screen all respond differently when being pulled , the | |
| 01:28 | mortar cracks and breaks . The wood bends and bounces | |
| 01:32 | back and the metal bends and keeps its new shape | |
| 01:35 | . But why do they behave differently ? You can | |
| 01:39 | easily see that the sand and the clay are made | |
| 01:41 | of small particles . But did you know that when | |
| 01:45 | we zoom many , many times into the screen in | |
| 01:47 | the wood , they are also made of tiny particles | |
| 01:51 | . We can think of the particles in the mortar | |
| 01:53 | sticking together like a row of people holding hands . | |
| 01:56 | When we pull on it , the people's arms straighten | |
| 01:59 | out and the chain stretches . Finally somebody loses connection | |
| 02:04 | the same way the particles in the mortar are pulled | |
| 02:06 | apart , The particles in the middle of the would | |
| 02:09 | stick together a bit differently in the wood , it's | |
| 02:12 | like suddenly something stretchy has been added to the connection | |
| 02:16 | between the people . When we pull Now the chain | |
| 02:21 | of people stretches a long way without anybody let him | |
| 02:24 | go . And when I stop pulling on the end | |
| 02:26 | , the people moved back to their original positions . | |
| 02:30 | Now , what if rather than being able to stretch | |
| 02:33 | the particles could just move around without breaking since they | |
| 02:38 | were all stuck together ? Watch what happens when we | |
| 02:41 | pull on ? Peter first deter drops the tightest string | |
| 02:45 | because is his lab mates to get pulled out of | |
| 02:48 | their original position without separating from them . Eventually as | |
| 02:53 | we pull , we end up with a very different | |
| 02:55 | shape than we started with , but the people haven't | |
| 02:58 | separated from one another and unlikely the stretch exercise bands | |
| 03:02 | , they don't get pulled back to their original position | |
| 03:07 | . We saw that the screen in the balsa wood | |
| 03:09 | bend when we pulled on it rather than breaking like | |
| 03:12 | the mortar in order to improve our mortar . Why | |
| 03:15 | don't we try combining the different materials to see if | |
| 03:18 | we can get a stronger material ? You can see | |
| 03:22 | jenny mixing the balsa wood with the mortar we created | |
| 03:27 | . And now jenny will do the same . She's | |
| 03:29 | mixing the screen with the mortar . Well , it | |
| 03:33 | looks like we got to put it in the oven | |
| 03:35 | to make this material . Let's test them . We | |
| 03:39 | saw for the wall that was made of just mortar | |
| 03:42 | . It broke very quickly . Let's see what happens | |
| 03:45 | for the one with balsa wood . As we can | |
| 03:47 | see the wall with the balsa wood is taking more | |
| 03:49 | weight to break than just the mortar did , but | |
| 03:52 | it isn't bending like the balsa wood did when we | |
| 03:54 | tested it by itself . Let's see how the screen | |
| 04:00 | does again . The screen and mortar mixer holds more | |
| 04:05 | weight than the wall of just the mortar , but | |
| 04:08 | it doesn't bend either . Mhm . And look how | |
| 04:12 | much weight we put in there . It's so strong | |
| 04:18 | . So what have we learned ? Medal in woods | |
| 04:20 | are able to bend without breaking and playing order camp | |
| 04:24 | . Yeah . So if we mix it with the | |
| 04:26 | mortar , we can make a wall that holds up | |
| 04:28 | better to being pulled on than one that doesn't have | |
| 04:30 | anything bendy in it . Mixing materials is something engineers | |
| 04:35 | do every day to make things work better in our | |
| 04:39 | world . And by thinking about the properties of the | |
| 04:41 | materials you choose , you can build not only strong | |
| 04:44 | wall but many more exciting things like skyscrapers , cars | |
| 04:49 | , computers or even spaceships . Yeah . |
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