States of Matter

 There are 3 states of matter: Solid, Liquid, and Gas. There is a theory named 'kinetic' or 'Particle theory' that explains these materials or particles are depicted as inelastic small balls.

For solids, the particles in a solid have a lot of attraction so that they don't get pulled apart easily. These particles can vibrate, but because of their strong attraction to each other, the particles are in a fixed position and don't move. 
But if we heat the solid up, it causes the particles inside the solid to vibrate quickly, causing them to reach their melting point, and then they break free of their bonds to turn into a liquid, which has very weak bonds between its particles and has the property of being able to change its shape to fit its container.
If we keep heating the liquid up, the particles' bonds will keep decreasing until there is no strength in the bonds and causing the liquid to turn into a gas.

These gases are strange because, since the bonds are very weak, the gas can occupy any container you put it in.
But if we heat up the gas in its container, it can either do one of two things. For example, if we use a balloon, it will expand the container, but if we use something rigid or fixed, like a metal can, it will cause the heat to build up into pressure.

If we cool the liquid, the weak forms of attraction will cause the bonds to be fixed in place, and if we cool it enough, it can cause the liquid to freeze.

If we are in a closed system, the change in states of matter will affect its density since the different states have different densities, but the mass stays constant as it is the same number of particles 

Fuses & Earthing

 When we use electricity, there are dangers to using it as it can cause fires, causing a power surge, and sudden changes in current, which are all dangers when handling electrical appliances. 

Ways to mitigate these dangers are with circuit breakers, fuses, double insulation, and grounded or earth wires.
Circuit breakers and fuses work in similar ways, but they have differences as they both cut power to the rest of the circuit when too much current flows through it. 

How a fuse works is that a live wire is connected by a thin metal wire that, when too much current flows through the live wire and, the fuse melt,s cutting power from the circuit and potentially saving the appliance from breaking or getting overloaded, and these fuses come in different ratings for different applications.

If we take an appliance that needs a 3a or 3 amp current, to add a fuse to it we can add a fuse that is 5a or 5 amps so that it will shut off the current to it if the appliance gets affected by a power surge.
Or if an appliance runs at 10a, then using a 13 or 12 amp fuse is necessary.

The reason why we use fuses is that its cheep and simple to use, thats why when we have appliances such as toasters and microwaves often have built in fuses in their plugs, one downside is that fuses are a one time use, meaning that once the fuse stops a power surge, it is permenently distroyed has has to be replaced. 

The other way to stop a current from flowing during a surge is via a Circuit breaker. Instead of being perminently damaged when a power surge happens, it instead "trips" which disconects it from the circuit so that no fuse is spent and can be used, thats why in breaker boxes when the power in your house trips, you can just flip a switch and have your electricity restored to your house.

One of the dangers of a power surge is that the live wire (brown) touches the appliance directly or the appliance's casing, which causes the appliance to be charge with electricity, one way to stop the acsedental shocks from the live wire touching the appliance is via a "earth wire' which is a wire that provides another path for the current that was previously flowing though the appliance to instead be 'grounded' and even if the live wire would be touching the appliance directly, the ground wire should protect you from getting shocked.

Another way is to double insulate an appliance, which basically means to add a non-conductive outer layer, which is most commonly plastic. If a device like a smartphone, tablet or appliance has double insulation, most of the time it doesn't need an earth wire, two layers to protect the user from being shocked

Plugs and wires

One important thing about electricity is the plugs and wires, and when you need to repair them, you might notice that the different coloured wires are inside a plug.

The power that comes from the national grid is the main power supply; the current of the mains is an alternating current with around 240 volts flowing into households.
Keep in mind that the voltage may differ between which goes into our sockets in our homes.

Three wires are in a plug: the live one, the grounded or earth wire and the neutral one, all with an insulating plastic covering the copper wires.

Now, the way we differentiate the wires so that we don't shock ourselves is through the colours. brown is live, meaning all the voltage flowing through the plug is going through the brown one and has a potential difference of 230 volts. The blue one is the neutral one that will complete the circuit.
And lastly is the earth or ground wire, which is a stripped green wire that stops the plug housing from becoming live and shocking us when we grab the plug.
It does this by giving the electricity an alternative output so that the power flows out instead of into the plug housing.

The reason why the electricity from the live wire (brown) flows through the neutral wire (blue) is that they have a 0 potential difference compared to the live wire, which has, in this case, 240 volts.
Now, since humans also have 0 potential difference, we can act as a neutral wire and get shocked by electricity, too. This is why sticking forks into plug sockets even when they are "off" can still shock you, and in general, sticking things into sockets is bad.

AC & DC Current

An Alternating current which is commonly referered as AC, which is a type of current that will alternate between a positive and negitive charge, and this charge will fluctuate between voltages.
If your house is being supplied with 240 volts then the AC current will fluctuate between 240v to -240v, and it will aternate between the voltages on a set timer.

While a direct current or DC current is either a positive or negitive charge, since the positive charge is consistant, the most common use is in which makes it good for cells and batteries.

We can get graphs of the potental difference from the current is via a Oscilloscope, which measures the potental difference a current is producing by displaying it on a monitor, these monitors display the current in a wave.

The National Grid

The National Grid is the network that distributes all the electricity in a city, usually the power comes from power stations, which normally produce lots of heat that then becomes thermal energy which then is turned into electricity.

The thing about power stations is that the amount of electricity they make is based on the amount of demand, the demand increases in the afternoon and evening, and since we use so much electricity in our daily lives, the power stations need to have extra capacity just in case, so often the stations run at much lower rate so that if there's a spike in electrical consumption they can output more power to satisfy the demand, which they can't do if they are running at high rates.

As we know the equation P=VT is power = voltage multiplied by time, but when high amounts of current flow through a wire, it causes the wire to heat up, this heat is then lost power, but if we need to transport this power all around the city or even the whole country this loss of power is extremely decremental.
But if we run a very low current, which is more efficient that would mean our voltage is going to be very high, meaning when we want to move the electricity around the country via the power lines and pylons we would need a way of increasing the voltage.

This is where Step-up transformers come in, they take the voltage from the power station and then turn up the voltage up to 400,000 volts then the cables transport it around the country.
Then after that, we would need a step-down transformer since 400,000 volts flowing into your house is too much if we were to pump that amount of voltage into a civilian house, firstly it would be very dangerous as if our devices or appliances they would explode having a high chance of losing lives.
In order to keep us safe from the high voltages is that we use a step-down transformer, that turns the 400,000 volts to roughly 230 volts. 

Parallel Circuits

Parallel circuits are circuits that have more than one loop, unlike series circuits, and each loop only has one component, making it more stable, meaning that if one component breaks, the whole circuit won't stop working.
We can also mix and match parallel and series circuits to add more components, an example of this is adding an on/off switch in the series circuit, which is connected to a parallel circuit.

Somthing different about parallel circuits is that since that all the compdennts get the same amout of potemntal difference, if we have a a parallel circuit with two compodents  on two loops and if the total amount of voltage going through the circuit is 4a, then either both compodents have the same amount of voltage taken (2a & 2a) each or they have an odd number like 3 & 1, if we add all of the amps in a circuit it should total to 4 reguardless. 

Eletricity likes to take the path of least-resistance, thats why electrical currents are stronger the lower the resistance the compident is, and the more compodents you add to a parallel circuit the lower the total resistsance will be,.

Series Circuits

Learning the difference between Series and Parallel circuits is important. 

In series circuits, the components are added in 'series' or in one line, as if they were all on one wire. The thing about this type of circuit is that if the wires break, the whole circuit stops working.
This also means that the potential difference is shared throughout the circuit.

You might get an equation like this :
Vtotal = V1 + V2 + V3.

If we were to put a 12-volt cell or battery, and have two filament lamps on the circuit, both lamps have to add up to 12 volts

On the other hand, current is the same everywhere in the circuit. To measure it, we use ammeters, which are placed in series, and since they measure current, we can place them anywhere in the circuit.

Resistance is how much the component resists electricity, and the total resistance is a sum of how much all components resist, so to calculate the resistance in ohms, we need to know how much power our components resist. 

So, let's take a circuit and connect two filament lamps, one lamp requires 4 ohms, and the other requires 2 ohms.
The total amount of ohms is about 6 ohms, since it is 2 + 4.

Let's use the same 6 ohm circuit above and calculate the resistance of a single component.
We can use the equation "V=IR", which is named Ohm's law, the 'V' in the equation means voltage.
So, first we find the battery, which is 12v or 12 volts. 
We then divide the 12 volts by 6 because that's how many ohms are flowing into the circuit, to get 2A or two Ammeters, then which then means that the component had 2A of resistance, then we multiply the 2A by 2 ohms or 2*2 to get 4 volts. 

Something to keep in mind is that Ammeters do have resistances, it is such tiny resistances that we can practically ignore them, now if we want to get the voltage of the second component, we would need to do the equation again, or we could just do 12-4 to get us 8.

Because we know how many volts are flowing through the circuit, which is 12, we can just skip doing the math, so doing 12-4 gives us 8, so that means that the second component needs 8 volts.

There is another way to find out how much voltage each component uses in the circuit by using a Voltmeter, which is connected in parallel to the component which we want to check, so if we connect it to the 8 volt component, it would display 8v.

Keep in mind that even though the voltmeter is connected in parallel,
we still consider the circuit to be in series, also the components that have a higher resistance will require more voltage, than components that resist less.

 

Charge, Current & Time

A charge is a measurement of current that flows through a window of time, such as the amount of charge that flows through a wire in a minute or hour. 

We write charge with the letter Q, and the name of this measurement for change is Coulombs, so an equation of this would be:
Q=A*T, or Q (charge), is equal to A which is amps, multiplied by T, which is time usually written in seconds unless specified. 

So in an equation, it would look something like this:

    "A kettle draws 12 amps and takes 50 seconds to boil, how much charge has passed          through the wire."

Since we have amps as the voltage and we were given an amount of time, the math is easy, first, we multiply the 12 * 50, which provides us with 600 coulombs or charge.

What about another equation:

    "A phone charger takes a total charge of 43.2Kc (43.2 kilo-coulombs) over 2 hours,             what amount of current has flowed through the wire"

First, we change the equation to match the problem, so we will use:
I=Q/T.

Now, we multiply 43.2kC by 1000. Since a kilo is 1000, we convert it to 43,000c or 43,000 coulombs.
However, since we use seconds instead of hours in our equation, we have to multiply 2 hours by 60 to get 120 minutes, then another 60 to get seconds. 
Which is around 7,200 seconds, now we just plug in the 43,000 / 7,200, which gives us around 6a or 6 amps. 

V = IR Equation & I-V Graphs

Let's take some amps and some ohms, and take 4a (4 amps), and 2Ω(ohms).

We would multiply the 4a * 2Ω, and it would be 8v or 8 volts, so if we take a 24v battery and it is producing the current of 8a, then it would be 24v/8a which would be 3Ω or 3 ohms.

Let's make a graph, shaped like a plus sign, and let's put the top number I for the current, and V for the differential difference. 
And it's a very straight line, a straight 45° incline. Now along as we are using wires and resistors that line will be very straight, but now if we add more resistors, the incline changes to around 25°, or if we use less it would be a more 75° incline. 

Now what about Filament lamps and Diodes, filament lamps work by heating up via electricity allowing them to emit light, now if we put in a lot of electricity to let the lamp glow, it starts to be weaker the more power we put in it since when the lamp heats up it increases resistance.

Now Diodes only work when the current is positive, how it works is they have they have a really strong resistance to negative currents.

Ciruits

 Most circuits are made out of components, and circuits are made in closed loops. 

The most common way a circuit is powered is by a cell, connected via a wire, one of the most common components in circuits are filament lamps, which are connected via the wire, and glow when connected to the cell or battery.

We can also connect a switch to the wire so that we can stop the flow of electricity from reaching the bulb. 

Sometimes you would write I electricity, when measuring electricity flowing through a wire they are named amps, or amperes are written with the letter A.

Potential Difference is the force driving the electricity around the wire, supplied by the battery or cell. It is like the pump that pumps the electricity through the wires.

Then, there is voltage, which is measured in Volts or V and is electricity supplied by the cell or battery.

Lastly, there is resistance which resists the flow of elections it slows down the speed of electrons we name it ohms using the Greek letter omega Ω

So when we are writing out a circuit, we first need a cell or battery, most commonly written by 2 lines, parallel to each other, one line taller than the other, the taller line is positive and the shorter one is negative, and electricity will flow from the positive side to the negative side.

Hydroelectricity & Tidal Barrages

Hydroelectricity uses large dams that prevent 'free-flowing' water by slowing the water down. 
Hydroelectric dams stop water from flowing from upstream to downstream, and after a while, these dams make reservoirs with lots of water closely resembling a pond.

How Tidal Barrages work on tides via the moon's gravity, twice a day we get high tide and using that high tide we trap the incoming water from flowing downstream. 
And when it starts to become low tide we release the water enabling us to gather electricity, these tidal barrages are built in estuaries which is where the rivers meet the sea. 

The way these work is they generate electricity using gravitational potential energy to generate electricity.
Inside the tidal barrages and hydroelectric dams are turbines under the water that turn when the water flows, they are then connected to a generator that produces electricity.

The pros of running these hydroelectric generators are that the running costs are low, these can be done on small to big rivers, hardly any pollution and are super reliable as an energy source.

But there are some cons, hydroelectric dams tend to flood areas since they have to release tons of water to generate electricity completely flooding natural habitats for animals and plants, and even flooding villages due to the large amount of water.
Along with the setup being expensive, due to the scale of the tidal barrages and hydroelectric dams.

Efficiency

When transferring energy from one form to another, there will be some energy lost during travel.
Like when you charge your phone using electrical energy and it goes into your phone's battery for chemical energy, it loses some of its energy due to heat. 

There is an equation for calculating useful energy:

Efficiency = Usefull energy output / Total energy input.

But if you are using Power:

Efficiency = Useful power output / Total power input.

Let's take two lamps, one powered by iridescent bulbs and one powered by LEDs, and let's say the iridescent lamp can convert 45 joules to light energy, while the LED can convert 225 joules into light lets figure out how many times more efficiently the LED lamp is compared to the iridescent bulb.

First let's give 300 joules of power to each bulb, and figure out which one is more efficient with the 300 joules. 

So we divide the 45 joules from the iridescent bulb by 300, then we get 0.15, and then we can calculate the LED bulb which is 0.75.
Then we divide the 0.75 by the 0.15 giving us 5, meaning the LED bulb is 5 times more efficient than the iridescent bulb. 
If you mess up the flip of the order of division, you will notice immediately because you will get a value bigger than 100% or a value bigger than 1.

Most of the time, you would want this in either decimal or percentage terms, so to get these numbers, you would need to multiply it by 100.
So, if you wanted to convert 0.15 and 0.75, you would need to multiply it by 100 to get 15% and 75%, then once again we can do 75% / 15% to get 5 again so that we know fully that the LED bulb is 5 times more energy efficient than the iridescent bulb. 
If we were to do the equation wrong, instead of dividing the 225 / 300.
We instead do 300 / 225, we would get 1.33 or 133%, which is impossible as you can't go over 100% in efficiency and not over 1 in decimals because this would be making joules of power which is incorrect because matter cannot be created or destroyed but it can be transferred.

Let's take a new subject, a microwave, with an efficiency of 70% and a total output of 800 watts. Once the equation is: Usefull power output / Total power input, it is 70% / 100% which is 0.7. So to get the useful power output we have to once again multiply the 0.7 by the power input of 800 watts.

So we multiply 0.7 * 800, and we get 560watts, as you know all devices leave some sort of waste when they are using energy, like when you use a electronic device some of the chemical energy and lose some energy in the form of heat.
But for things like electronic heaters, the "wasted energy" is then turned intoT

Reducing Unwanted Energy Transfers

To reduce unwanted energy transfers the most common types are insulation and lubrication. 

For example, when you want to keep a drink cold in a cooler box with ice, you are insulating the box to keep it cold.
This is the same as closing all the windows in your house to trap heat or cold air so that it doesn't escape through convection. Then we have to reduce the heat loss from solids which is conduction, to combat the loss of heat houses are built with thick walls to keep the heat trapped. But certain walls have gaps between the outer and inner walls, which is a space that can also lose heat, so we put an insulator (usually foam) between the outer and inner walls of the house to trap the heat in.
Windows are also important to help reduce the amount of heat or energy lost, and the amount of glazing on the window pane.

Now about lubrication, which is used in all kinds of machinery, typically oils or greases, from wheels to ball bearings, to doors moving, if it moves normally it's pretty oily to the touch and was lubed to make it move smoother.
This also helps with reducing heat conduction which

Conduction, Convection & Radiation

There are multiple ways heat can be transferred between objects. 

Conduction happens through solids, Convection through liquids, and Radiation through the air.

Let's start off with Conduction, first, we take a metal bar, since it is solid, the particles are very highly knit so it is very easy for it to transfer heat, so when we heat up the metal bar with a Bunsen burner, the particles start getting charged with kinetic energy causing them to move a lot and since they are so tightly knit the heat is transferred throughout the solid.

If you heat certain materials, you might notice that they can be heated to different temperatures. That is called "Thermal Conductivity." For example, metals have much higher thermal conductivity than plastic, which has very low thermal conductivity. 

Convection occurs when you heat up any liquid or gases.
The heat charges the particles with kinetic energy, causing them to move from the warmer regions to the colder regions.
When it is colder, the particles are less spread out than in the warmer regions.

That is why when you heat things up, they expand slightly, and when liquids or gases heat up, they become less dense because the particles are no longer near each other. 

This is why we wear blankets when we sleep in cold environments which keeps the warm air from our bodies from escaping the covers. 
And why do we have to close the windows and doors to keep the cold air from an air-cond from flowing out of our homes, or aircon's, oceans and heaters use a Convection Current to keep the fluids or air circulating.

The thing that convection and conduction have in common is that both have particles gaining kinetic energy, but what separates these is that only the energy is transferred while convection is that the particles move. 

Radiations are when energy is transferred via air or a vacuum, a good example of this is the sun's rays, which are transferred by solar radiation going through space which is a vacuum into our atmosphere, same with a microwave. 
Radiation travels using infrared waves, all objects absorb and emit radiation, how hot an object is and how much radiation it emits. Hence the sun and its heat, and why you cook food around it is hot.

Conservation of Energy

The first law of Thermodynamics is that energy can be transferred, stored and dissipated but cannot be created nor destroyed.

For example, when you plug your phone into a socket to charge it, electrical energy is turned into chemical energy in your phone's battery. And using the chemical energy that was being charged by the electrical energy from the socket to power things such as the screen which turns the chemical energy into light energy, or play sounds by converting it into sound energy. 

But you can never have 100% energy transfer, it's because there will always be wasted energy.
Most wasted energy is lost due to the energy generating heat, like when you are charging something your phone gets warmer, or a car tyre is spinning rapidly causing friction which causes the tyre to get warmer.  

There are types of systems: closed and open systems. First, we have to select one. Let's say we take your phone as a system. The system would be the phone, while the outside world would be named the "environment." In this case, the phone would be an open system because it can be affected by the environment or outside factors. Because this is an open system, energy can flow between the environment and the system.

While a closed system stops all outside factors or the environment entirely.
If you put your phone in a sealed jar. Everything inside the jar is the system, and because it is in a sealed jar it is not affected by outside forces or environment factors.
So when the phone heats up, the heat is trapped inside the jar and it stays within the system.

Internal Energy and Heat Capacity

Internal energy usually comes into two forms: Potential Energy stores, and Kinetic Energy stores.
Most potential energy stores come from Gravitational and Elastic energy, this isn't really related to temp but is good to know. Kinetic energy on the other hand is very important as the movement is an energy store.

When you heat up anything, you are converting the heat into kinetic energy stored which we can measure in an increase in temp, which is a measure of the "Internal temperature" of a substance.  

However, substances need more energy to increase their temperature than other elements, as water needs 4200J or 4200 joules of heat in order to warm 1kg of it by 1°c. 
Compared to Mercury which only needs 139J of energy to have 1kg of it to be 1°c  hotter. These numbers are called "Heat Capacity."
The inverse is also true, so when water cools by 1°c, the water is relicensing 4200J of energy while cooling. 

Gravity and Weight

The Earth's core is the reason why Gravity exists, gravity is a force that attracts objects together and relies on mass as well as the distance between the two objects,
that is why when you travel in the ozone layer gravity is weaker. 

Everything has a gravitational force pulling things towards it, like an apple and a skyscraper, there is a gravitational pulling the apple and skyscraper together but it is so slight that it is practically non-existent. 

For large objects, or in this case.
Planets, have a much stronger gravitational pull than an apple, having a file of influence around it. We, humans, have dubbed this a "Gravitational field" and the strength is the "Gravitational field strength" In, in Physics we show the letter "g" as gravity, which if we are talking about Earth is around 9.8 newtons per kilo, but if you take the moon it would be 1.6 newtons per kilo because the moon is smaller and thus has a smaller mass.

So whenever an object comes into a gravitational field it is attracted or pulled towards the gravitational field, so to calculate an object's weight, we take its mass and multiply it by the gravitational field strength (9.8) so if someone weights 60kg, we multiply 60 * 9.8 giving us 588 newtons or 588N. For this, we would say we have a weight of 60kg, not a mass of 60kg.
Mass refers to the basic characteristic of the object's mass, and Weight is how much the force of gravity affects it.

When you jump you are expending energy and putting it in the "Gravitational potential energy store", the formula for gravitational potential energy store is 
Ep = mgh or Mass * Gravitational field strength * height the measurements are mass (kilos), gravitational field strength (newtons per kilo) and H (Height), and Ep is measured in Joules.

Now let's take an apple with a mass of 100 grams and we throw it 3 meters into the air.
First, we have to convert the mass to kilograms to make the equation easier, so we convert the 100g to 0.1kg by dividing the 100g by 1000 (because one kilo is 1000 grams). Then we multiply the 0.1 (weight) * 9.8 (the gravitational field strength) * 3 meters (height), and we get 2.94 joules of energy.

Once again gravity relies on the mass of an object and how far it is from other objects, so planets will attract space debris, but rocks cannot attract other rocks on earth, because of the mass difference between a planet and a rock.

Kinetic Energy

 Kinetic energy relies on the Speed and Mass of the object, so the faster the object is moving the more kinetic energy is stored.
But if two objects move at the same speed, the object with more mass will move faster.

Let's take two objects, one ball and a plane, let's say the ball mass is 0.1kg and is moving at 4,000 m/s, and the plane is 20 tons moving at 5m/s, now it's not clear which is moving faster.
To figure out which object is moving faster we can use the equation of:

Ek = 1/2MV^2.

The E is Energy, while the K means it is kinetic, so Ek is = "Energy Kinetic", M is mass which is Kg in this case, and V means Velocity.

Now let's do the Equation, the most important is to keep the mass the same, so let's turn the 20 tons into 20,000kg, and to make it consistent we can do the 0.1 ball weight and divide it by 1,000 to get 0.0001kg. Now it is ready to be plugged into the equation.

First, we have to get the 1/2 or 0.5, so we put: "0.5 * 20,000 * 5^2" (this is 5 squared or 5*2, keep in mind that it is the speed being squared not the whole thing.
Now doing the equation gets us 250,000 Joules, which we rewrite as 250,00kj.
But for the ball, it is "0.5 * 0.0001 *  4,000^2" which equals to about 800 joules or 0.8kj, so the plane flying at 5m/s with the weight of 20,000kg is travelling around 312.5 times faster than the 0.1kg ball going at 4,000m/s.

Stored Energy

The first law of Thermodynamics Energy is neither created nor destroyed as it can only be transferred between different forms and objects.

There are different types of energy:

Thermal which comes from heat like volcanos. 

Kinetic energy is energy coming from movement.

Gravitational potential energy, energy comes from the position of a thing in a Gravitational field.

Elastic potential energy mainly comes from springs and rubber bands. 

Chemical energy comes from chemical bonds.

Magnetic energy comes from Magnetic fields. 

Electrostatic energy which normally happens when you walk and shock someone.

And Nuclear energy comes from splitting atoms apart.

There are many ways to transfer types of energy, by using your arm to pull an elastic band, you are turning your Mechanical energy into elastic energy, electrical energy by plugging things into sockets to power them, or by light or sound waves.

When we take a group of objects, we can name that a system, in this system, energy is transferred to each object, but in an "Open System" the objects in the system can exchange energy from the outside world.

Let's take an electric kettle and fill it with water, when you turn on the power to boil the water in the kettle, the heating element uses the electric energy and turns it into heat that then transfers to the water to boil it.

There is also something named Work Done, mainly Mechanical and Electrical, mechanical work is when force is used to move an object, and electrical work happens when electricity flows between.
For example, let's say a train is moving along the track, and the tracks ahead crash down and now there is a large gap that the train will hit if it keeps going it at speed.
What the train driver will do is hit the brakes, which causes friction between the wheels and the track, slowing the train to a stop, the reason why this works is is because the kinetic energy from the train movement to thermal energy and heat due to friction.
That is why when you are going very fast and slam the breaks, the breaks themselves will heat up, and when you slide your hand fast on a smooth surface it gets hot.