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hi guys I would like to explain you what is energy and the things that you have

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to know this year about energy okay so energy we could say that energy is the

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ability to produce a change so we say in our everyday life that we feel very

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energetic when we have energy when we can do things so we will say that energy

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is the ability to produce a change and as any other physical magnitude we have

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to be able to measure energy and to use a unit so it's a physical magnitude

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physical magnitude and as any other physical magnitude it has a unit okay

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that in the international system the unit is the joule okay and we write it as a big J or an

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uppercase J okay there are different types of energy for example light energy thermal energy

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light energy that we receive from the sun or from a light bulb and thermal energy that we also

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reside from the sun or maybe from a heater okay and we also have sound energy that is produced by

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a loudspeaker so that there are different types of energy and we can transfer the energy from one

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body to another or transform the energy from one type of energy to a different type of energy so we

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have energy of type 1 imagine for example light energy or luminous energy

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and we can transform this energy in other type of energy for example heat or

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thermal energy okay so in this transformation the energy is constant so

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So the amount of joules that we have here is the same than the amount of joules that

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we have here.

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So energy can be transformed or transferred but it remains constant and this is a conservation

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law which says that energy is constant.

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can transform it we can transfer it energy cannot be created neither created

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nor destroyed okay so can be only transformed or transferred for example

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if there is a ball on the ground and I kick the ball part of the energy of my

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muscles are transferred to the ball that will start moving and when you have

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motion that's mechanical energy okay so the next thing that I want you to

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know is that one of the most important types of energy we are going to learn in

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physics is energy due to position or speed position it means the height okay

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so and the energy that is related with position will be called a potential

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energy and the energy related to the speed will be called kinetic energy and

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if we add these two energies together what we obtain is the mechanical energy

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so this plus this is mechanical energy so we can say that mechanical energy

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this is mechanical equals potential energy plus kinetic energy potential

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energy plus kinetic energy okay and we are going to learn now what is the

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equation that is going to enable us to calculate the energy for kinetic and for

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potential energy okay I would like to highlight in some way this equation and

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then potential energy this one potential energy as I told you it depends on the

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height but it also depends on the mass and on the gravity so it's

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going to be the mass times the acceleration of the gravity times the

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height so M is the mass and we measure it in kilograms so we should add the

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mass in kilograms in this equation G is the acceleration of the gravity and on

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the surface of the earth is 9.8 meters per second square and finally H is the

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height and we measure this in meters okay this m is mass and this m is

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meters so please don't confuse them okay so this is the equation for potential

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energy so you see that the more mass has an object the more the energy that it

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has and the tallest or the highest the higher that is an object the more

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energetic it's going to be and then we can express potential kinetic sorry

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kinetic energy as one half times the mass times the speed squared okay and we

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can use this second equation to calculate the kinetic energy M is the

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mass and V is the speed and we measure the speed in meters per second okay let's

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try to solve an example to illustrate this okay so imagine that we have this

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is an example imagine that we have a lorry okay so imagine that there is a

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bridge and here is the ground round level there is a bridge imagine there is

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a bridge and there is a lorry crossing through the bridge and you imagine that

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the mass of the lorry is 10,000 kilograms okay and the lorry is moving

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at the speed of 25 meters per second okay and this bridge imagine that is 10

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meters tall okay and we want to calculate the kinetic energy the

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potential energy and the mechanical energy okay this is what I want you to

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calculate so let's start let's start with the kinetic energy it's going to be

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one half times the mass times the speed squared so this is one half the mass is

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10,000 and the speed squared is 25 squared as we are writing everything in

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international system units we will obtain the result in joules okay so I

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have to find my calculator here this and this is 25 squared times 7,000 over 2

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and this is three million one hundred and twenty five thousand joules okay

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then the second thing that we need to calculate is the potential energy that

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equals M times G times H okay and this is going to be M is ten thousand again

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in kilograms, g is 9.8 and the height is 10 and if you calculate that is 980,000

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joules and then finally the mechanical energy is the kinetic plus the potential

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so it's 3,125,000 plus 980,000, so if we calculate that, this is 4,105,000 euros,

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okay, and this is the third thing, or the third noun we have to calculate,

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so this is the energy that something has just by the fact of being moving and not being on the

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ground being elevated okay so when you see this video you could do the homework that i have

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proposed and that's all for now okay i hope you continue being well i'll see you soon bye