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Hello, today we are going to learn Unit 5 from Natural Science, Heat, Light and Sound, or Sound, Light, Heat, I think that's the title in the book.

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So we start with the first page, number one, sound. We are going to start explaining sound, is there sound in space?

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space? Well, we know that when an object vibrates it produces sound waves. And what's that?

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Sound waves can travel through a medium, liquids, solids and gases. So, sound waves can travel

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through water, through a rock or through air. Nevertheless, they can't travel through a

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vacuum, the space. No puede viajar en el vacío, por el espacio. And sound waves can also travel

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faster through water than through air, ok? Viajan más rápido por el agua que por el

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aire. Why? Because in water the particles are closer together, so energy vibrations

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are passed quicker from one particle to another compared to air particles, ¿vale? Las partículas

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of the water, they are closer together and then they pass between them much faster

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so these are sound waves and you can find there a picture

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number two is about light, what is a light source?

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well, light is a form of energy that allows us to see objects

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if there is no light we cannot see

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so we can classify light sources into artificial

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which means that they are man-made, such as a torch or a lamp, or natural, such as lightning

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or the sun. We can find these light sources, natural light sources, in nature.

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Characteristics of light. Light has three characteristics, speed, direction and color.

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the speed well light is the fastest form of energy it travels are 300,000

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kilometers per second which is a lot direction light travels in a straight

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line and this is called rays los rayos del sol straight line linea recta always

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and can't pass through all materials no puede traspasar todos los materiales so

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according to the materials light can pass through they can be these

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These materials can be classified into three, opaque, los opacos, do not allow any light

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through them, no puede pasar la luz a través de ellos, por ejemplo una puerta, si una puerta

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está cerrada la luz no puede atravesarla.

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Translucent materials allow some light through them, materiales translúcidos, por ejemplo

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una mampara de la ducha, si en las que tenéis en casa algunas son transparentes y otras

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and transparent materials allow all the light through them

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the third characteristic of light is color

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light appears white but it's composed by the seven colors of the rainbow

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Nos parece blanca, pero está compuesta por los siete colores del arcoíris.

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When light touches an object, it can be absorbed, reflected or refracted.

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¿Vale? Cuando la luz toca un objeto, esta luz puede ser absorbida, reflejada o refractada.

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¿De acuerdo? Lo vamos a ver en la siguiente diapositiva, in the next slide.

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Light properties, propiedades de la luz.

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we have three, one of them is reflection, light hits an object and bounces back

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es decir que rebota, la luz toca un objeto y rebota

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y depende de cómo sea este objeto, este objeto puede tener una superficie smooth

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o una superficie rough, o lisa o rugosa

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when the surface is smooth all the rays reflect in the same way

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me miro al espejo y ese espejo me devuelve mi imagen tal y como es

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When the surface is rough, all the rays reflect in different directions.

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Y significa que si la superficie es rugosa, como el ejemplo que tenéis en la pantalla,

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esos espejos que tienen formas, ¿verdad? No son espejos totalmente rectos, son cóncavos, convexos,

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hacen formas raras, la imagen que me devuelven no es la mía, no es la real, es una diferente a la real.

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also we have refraction, light changes directions when it passes from one medium to another

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for example from air to water

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as you can see in the example we have a glass of water with a straw

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con una pajita

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la imagen parece que la pajita se dobla, ¿verdad?

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y esto es porque una parte de la pajita la luz está pasando a través del aire

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y de repente cuando toca el agua

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es que la luz atraviesa el agua

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con lo cual está viajando

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la luz cambia de dirección

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cuando pasa de viajar por el aire

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a viajar por el agua

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no tiene nada que ver, ¿vale?

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se refracta

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How are rainbows formed?

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¿Cómo se forman los arcoiris?

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tiene que ver con la diapositiva anterior

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con el refraction, ¿vale?

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Rainbows are formed through refraction

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and you have a picture there

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So, when I see light, light travels through air and suddenly when it rains, it touches a raindrop, una gota de lluvia, it touches a raindrop and this raindrop is made of water, so light travels from air to water, yes, and light is reflected, turning the sunlight, which is white, into the seven colors of the rainbow.

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we also use refraction to see

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we use glasses

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which are carved pieces of plastic

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or glass and mirrors

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cuando alguien no ve bien

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sin gafas

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es porque tiene miopía, etc

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bueno, pues necesito unas gafas para ver

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estas gafas tienen

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diferentes tipos de curvaturas

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son curvas porque lo que hacen es que

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funcionan como una lente

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me acerca o me aleja los objetos

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para que yo los pueda ver

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apropiadamente

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Now we are going to talk about heat. What is the difference between heat and temperature?

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Heat is thermal energy which can travel in any direction, so heat travels in any direction,

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any. Do you remember that before we were talking about other forms of light and sound and they

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cannot travel in any direction they can travel in a straight line you remember

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that but so heat can travel in any direction heat is energy and temperature

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measures how hot or cold something is so that's the difference and heat is the

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energy and the temperature is measures how hot or cold something is

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para medir el calor, el calor o lo frío que hace. We have two sources of heat, natural sources such

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as the sun or the geothermal energy and then we have other sources which are artificial such as

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the central heating for example or gas. Properties of materials, depending on how some materials

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transfer the heat we can classify them into two, thermal insulators or thermal conductors.

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The thermal insulators don't transfer heat very effectively, so they are not metals, that means that if I, for example, when it's very cold, I put on a lot of clothes to cover myself, why?

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Why? Because the clothes, the fabric, as well as the plastic and other materials that are not metals, are good insulators of heat.

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That is, they keep me warm. The clothes keep my body warm and prevent the cold from reaching my body.

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On the other side we have the thermal conductors. They are mainly metals and they transfer heat very effectively.

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That's why, for example, if there is something boiling, they are cooking in the kitchen and I put a knife inside, I burn myself and the knife is like the one you see in the drawing because it is a metal and metal is a good conductor of heat.

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However, wood is not. That's why most of the kitchen utensils are made of wood or plastic, because they are not heat conductors and they can prevent me from burning myself.

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Effects of thermal energy. Heat can change the state of matter. So we have three kinds of changes.

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The first one is melting, so when something is very, very, very, very cold and I heat it, it melts.

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Evaporation, the same if I fire water and I heat water, it evaporates.

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And then we have expansion and contraction, they are opposites.

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Expansion is when I apply heat to one substance, it expands, such as the thermometer and the mercurial.

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So, when I apply heat, then the mercury, what it does is that it grows

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And the opposite, contraction is right the opposite, if it's cold, it contracts, and that's it

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Ok, that's all, so I keep this for you in case you need any help

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And if you need any questions, if you need to ask anything, if you have any questions, please write to me to professedincomesanoromanos.com and that's it. Bye bye.