Introduction to Thermal Physics

Summary

This lesson introduces thermal physics, focusing on the concept of internal energy and its relationship with heat and temperature. It explains the particle model of matter and how it applies to different states of matter. The lesson distinguishes between heat and temperature, linking internal energy to both potential and kinetic energy. It also covers the importance of the Kelvin scale and the first law of thermodynamics, illustrating how changes in internal energy occur through work and heat transfer.

Takeaways

• 🔍 The lesson introduces the concept of internal energy in thermal physics, aiming to differentiate between heat and temperature, and link internal energy to kinetic and potential energy.
• 🌡️ The particle model of matter explains the arrangement and movement of particles in solids, liquids, and gases, which is crucial for understanding thermal physics.
• 🔵 In solids, particles vibrate but cannot move from their fixed positions, indicating high inter-particle forces and little movement.
• 💧 In liquids, particles vibrate and move freely but maintain contact, showing moderate inter-particle forces and movement.
• 🌀 In gases, particles move randomly with high speeds and almost no inter-particle forces, resulting in very high movement and very little force of attraction.
• ⚖️ Temperature is a measure of the average kinetic energy of particles in a substance, with the Kelvin scale directly linking temperature to kinetic energy.
• ❄️ Absolute zero (0 K or -273 °C) is the theoretical limit where particles have zero kinetic energy, representing the lowest possible temperature.
• 🔄 Internal energy encompasses both the kinetic and potential energies of particles within a substance, and it changes with temperature or state changes.
• 🔄 The first law of thermodynamics states that the change in internal energy of an object is equal to the total energy transfer due to work and heat.
• ♻️ Energy can be transferred between particles in a substance, but the total internal energy of a closed system remains constant unless work is done or heat is added/removed.

Q & A

What is the main focus of the lesson on thermal physics?

The main focus of the lesson is to understand and apply the concept of internal energy, including the difference between heat and temperature, and linking internal energy to potential and kinetic energy.

How does the particle model of matter explain the states of matter?

The particle model of matter explains that in solids, particles are in a fixed structure with high forces of attraction and little movement. In liquids, particles can move and are in contact with each other with moderate forces of attraction. In gases, particles move freely with almost no forces of attraction and high movement.

What is the relationship between temperature and the average kinetic energy of particles?

Temperature is a measure of the average kinetic energy of the particles in a substance. As temperature increases, so does the average kinetic energy and speed of the particles.

Why is the Kelvin scale considered more fundamental than the Celsius scale?

The Kelvin scale is considered more fundamental because it is an absolute scale based on the properties of gases, with a defined zero point (absolute zero), whereas the Celsius scale is based on the arbitrary properties of water.

What is the significance of absolute zero in the Kelvin scale?

Absolute zero, at -273 degrees Celsius or 0 Kelvin, is significant as it represents the theoretical limit where particles have zero kinetic energy and would not move, indicating the lowest possible temperature.

How does the internal energy of a substance relate to its kinetic and potential energy stores?

The internal energy of a substance is the sum of the kinetic energy (due to particle motion) and potential energy (due to intermolecular forces) of all its particles.

What is the first law of thermodynamics as it pertains to the change in internal energy?

The first law of thermodynamics states that the change in internal energy of an object is equal to the total energy transfer due to work done on the object and heating.

How can the internal energy of a system be increased?

The internal energy of a system can be increased by transferring energy to it through heating or by doing work on it, which can change either the potential or kinetic energy stores of the particles.

What are the two ways work can be done to change the internal energy of a system?

Work can be done to change the kinetic energy store, which affects temperature (covered by specific heat capacity), or to change the potential energy store, which affects the state of the material (covered by latent heat).

How does the change in state of a substance affect its internal energy?

Changing the state of a substance, such as from ice to water to steam, can change the amount of internal energy due to changes in the potential energies of the particles, even though the kinetic energies remain constant.

Outlines

00:00

🔍 Introduction to Thermal Physics

This paragraph introduces the topic of thermal physics within the AQA A Level Physics curriculum. It emphasizes the importance of understanding internal energy and its relation to heat and temperature. The lesson aims to clarify the differences between heat and temperature, link internal energy to kinetic and potential energy, and apply equations to calculate internal energy. The particle model of matter is introduced as a foundational concept, explaining how particles are arranged and move in solids, liquids, and gases. The model helps to understand the properties of different states of matter and the energy possessed by particles in these states.

05:00

🌡 Understanding Temperature and the Kelvin Scale

This section delves into the concept of temperature, explaining it as a measure of the average kinetic energy of particles in a substance. It contrasts the Celsius scale, which is based on the properties of water, with the Kelvin scale, which is an absolute temperature scale. The Kelvin scale is derived from the fundamental properties of gases and is crucial in thermal physics. The paragraph also discusses the relationship between temperature, particle speed, and the distribution of particle speeds in gases at different temperatures. It highlights how the average particle speed and kinetic energy increase with temperature, and how the spread of particle speeds widens.

10:02

🔄 Internal Energy and its Components

The paragraph discusses internal energy, which is the sum of kinetic and potential energy stores within a substance. It explains that internal energy includes both the energy due to particle movement (kinetic energy) and the energy due to intermolecular forces (potential energy). The concept of absolute zero is introduced as the temperature at which particles have minimal internal energy, with only potential energy present. The distinction between the Kelvin and Celsius scales is clarified, with the Kelvin scale starting at absolute zero. The paragraph also touches on the idea that changing the kinetic or potential energy of a substance's particles will change its internal energy.

15:04

🔧 Work and Energy Transfer in Thermodynamics

This final paragraph explores how internal energy can be altered by heating or doing work on a system, which is a fundamental concept in thermodynamics. It explains that work can change the kinetic energy store, affecting temperature, or the potential energy store, which can change the state of the material. The paragraph summarizes the key points of the lesson, reinforcing the understanding of internal energy, the difference between heat and temperature, and the role of potential and kinetic energy. It also previews upcoming topics, such as specific heat capacity and latent heat, which will be covered in subsequent lessons.

Keywords

💡Internal Energy

Internal energy refers to the total energy contained within a system. It is the sum of all the kinetic and potential energies of the particles that make up the system. In the context of the video, internal energy is a key concept in thermal physics and is directly related to the temperature and state of a substance. The script explains that internal energy is the sum of the kinetic energy, which is due to the random motion of particles, and potential energy, which is due to the forces of attraction between particles. The video uses the example of ice, water, and steam to illustrate how internal energy changes as substances change state.

💡Kinetic Energy

Kinetic energy is the energy that a body possesses due to its motion. In the video, it is described as the energy that particles have because they are in constant motion. The script links kinetic energy to temperature, stating that temperature is a measure of the average kinetic energy of the particles in a substance. As temperature increases, so does the average kinetic energy, leading to faster particle movement. This concept is crucial for understanding how thermal energy is transferred and how substances react to changes in temperature.

💡Potential Energy

Potential energy is the stored energy of an object due to its position or condition relative to other objects. In the script, potential energy is discussed in relation to the forces of attraction between particles within a substance. It is part of the internal energy and can change when the substance undergoes a phase change, such as melting or boiling. The video emphasizes that while kinetic energy is associated with particle motion, potential energy is associated with the forces that hold particles together.

💡Thermal Physics

Thermal physics is a branch of physics that deals with the effects of heat and temperature on matter. The video introduces thermal physics as part of the AQA A-Level physics curriculum and focuses on understanding concepts like internal energy, heat transfer, and the particle model of matter. The script explains how thermal physics uses statistical methods to understand the behavior of particles in a substance and how this knowledge is applied to calculate internal energies and understand phase changes.

💡Particle Model of Matter

The particle model of matter is a conceptual framework that describes matter as being composed of particles with specific properties such as volume, mass, and motion. The video uses this model to explain the different states of matter (solid, liquid, gas) and how the arrangement and movement of particles change with temperature. The script illustrates how in solids, particles vibrate but do not move from their fixed positions, while in liquids, they vibrate and move around, and in gases, they move freely with little attraction between them.

💡Temperature

Temperature is a measure of the average kinetic energy of the particles in a substance. The video script explains that temperature is directly proportional to the average kinetic energy, meaning that as temperature increases, so does the average speed of the particles. The script also differentiates between heat and temperature, clarifying that heat is the transfer of energy due to a temperature difference, while temperature is a measure of the energy within a system.

💡Heat

Heat is the transfer of thermal energy between two systems or particles due to a temperature difference. In the video, heat is discussed in the context of how it affects the internal energy of a substance. The script mentions that heat can increase the kinetic energy of particles, leading to a rise in temperature. It also touches on the concept of heat transfer being a mechanism for changing the internal energy of a system.

💡Phase Change

A phase change is the process by which a substance transitions from one state of matter to another, such as from solid to liquid or liquid to gas. The video script uses phase changes to illustrate changes in internal energy. For example, when ice melts into water, it absorbs heat, which increases its internal energy due to an increase in potential energy, even though the temperature remains constant.

💡First Law of Thermodynamics

The first law of thermodynamics, also known as the law of energy conservation, states that energy cannot be created or destroyed, only transferred or changed from one form to another. In the video, this law is discussed in the context of changes in internal energy. The script explains that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system. This principle is fundamental to understanding how energy is transferred and conserved in thermal processes.

💡Absolute Zero

Absolute zero is the lowest possible temperature, at which particles have minimal motion and theoretical kinetic energy is zero. The video script describes absolute zero as the point at which a gas would exert no pressure, which is -273 degrees Celsius or 0 Kelvin. This concept is important in thermal physics as it represents the point at which the internal energy of a substance is at its minimum, consisting only of potential energy.

Highlights

Introduction to thermal physics, part of AQA A Level Physics.

Understanding the concept of internal energy.

Describing the difference between heat and temperature.

Linking internal energy to potential and kinetic energy.

Using equations to calculate internal energies.

Comprehensive understanding of the particle model of matter.

Different formations of particles in solids, liquids, and gases.

Particle model of matter for approximating properties of states of matter.

Demonstration of particle movement and energy in different states.

Recap of the particle model of matter for solids, liquids, and gases.

Thermal physics contains many assumptions and approximations.

Temperature as a measure of the average kinetic energy of particles.

Graph showing the link between temperature and average kinetic energy.

The Kelvin scale directly links to the kinetic energy and speed of particles.

Zero degrees Kelvin means particles have an average kinetic energy of zero.

The Celsius scale is based on the properties of water and is not absolute.

The Kelvin scale is derived from fundamental properties of gases.

Absolute zero is the lowest possible temperature and is zero degrees Kelvin.

Internal energy includes both kinetic and potential energy stores.

The first law of thermodynamics relates to the change in internal energy.

Internal energy can be increased by heating or work done on the system.

Work can change the kinetic or potential energy store of a material.

Summary of the lesson on thermal physics and its significance.

Transcripts

hello and welcome to today's lesson on

an introduction to thermal physics

which is part of the thermal physics

topic in aqa a level physics

so in today's lesson we're going to try

and understand and apply the concept of

internal energy so if we've been

successful

and learnt in today's lesson we should

be able to describe what the difference

is between heat and temperature

link the idea of internal energy to

potential and kinetic energy

and then finally use equations to

calculate internal energies which links

into the following part of the aqa

a-level physics specification

3.6.2.1 thermal energy

transfer now to fully understand the

concepts in thermal energy

you've got to have a comprehensive

understanding of the particle model of

matter

now the particle model of mata shows the

different formations of particles in the

different states of matter

now the particle model of mata is good

for approximating the properties of

solids liquids and gases now when

particles change state

the particles that make them up change

the way that they are

arranged as shown in the following image

now it's actually

better to show the particle model when

looking at the movement of the particles

as this also allows you to show the

energies that the particles possess

in the different states so you can see

the movement and energy possessed in a

gas

a liquid and a solid so let's just recap

very quickly the particle model of mata

so in a solid the particles are arranged

in a regular fixed structure

they can't move from their position in

the structure but they can vibrate

so in solids we say that there's a high

force of attraction between the

particles

but little movement of particles the

particles and solids will only vibrate

whilst in a liquid the particles vibrate

and are free to move around but are

still in contact with each other

the forces of attraction between them

are less than when they're in a solid

form

so in liquids there's moderate forces of

attraction

and moderate movement of the particles

whilst in the particle model of mata for

gases

the gas particles are free to move

randomly in all directions with

high speeds and there are almost no

forces of attraction between them

so in gases there's very little forces

of attraction

and very high movement of particles now

if we understand

the particle composition of solids

liquids and gases

we can start to consider the principles

of thermal physics

now as we're working on a particle level

this shows that thermal physics contains

many assumptions and many approximations

so we're not considering the idea of

nuclei

or protons neutrons and electrons we're

just considering

particles as a solid sphere now the

assumptions that you use

in your particular calculation which you

state in your answer are just as

important as the answer

the answer value itself all thermal

physics is an example of what we call

statisticial physics

we assume that we are dealing with many

particles

now when a substance is heated the

particles will

move or vibrate faster as the average

kinetic energy

in the particles has increased so we can

say

that temperature is a measure of the

average kinetic energy of the particles

in a substance

for example a substance at 24 degrees

kelvin

would have particles on average with

less kinetic energy than a substance at

200 degrees

kelvin now as we can show in the

following graph

we can look at how the temperature of a

gas

links the average kinetic energy or

speed of the particles in

that substance so a substance with a

high temperature

means that the particles are vibrating

or moving with higher speeds on

average compared with the substance of

the lower temperature

now it's important to note that as

kinetic energy is a scalar term

the fact that the different particles

are moving in different directions is

irrelevant

which is why particle speed is always

discussed in thermal physics and

not particle velocity now if we use

the kelvin scale for temperature the

temperature directly links to the

kinetic energy and the speed of the

particle

so therefore zero degrees kelvin means

that the particles will have an average

kinetic energy of zero

now you can see it in the following

particular animation at zero degrees

kelvin or

absolute zero their particles have an

average kinetic energy zero

they are at rest so we can say that

temperature is a measure of the average

kinetic energy of the particles in a

substance

now we can use classical mechanics

because the particle model relies on the

newtonian laws of motion

so from the idea of classical mechanics

we can say that temperature is directly

proportional

to the average kinetic energy of the

particles so therefore temperature is

directly proportional

to a half times by mass times by average

speed squared

now there is a physical constant which

links the temperature

of a substance with the average kinetic

energy of the particles in the substance

which is called the boltzmann constant

which we'll look at later

now as we go back to this following

graph this graph shows the distribution

of particle speeds for a gas

now it's important to note that the

particles in a gas do not travel

at the same speed and the speed

distribution of the gas particles as you

can see on the graph

depends on the temperature some

particles will be moving fast but

others will be moving much more slowly

but most of the particles in the gas

will travel around

at the average speed now this is

important because it shows us a few key

ideas when we look at the different

temperatures

and the distribution speeds in a gas so

it tells us that firstly as the

temperature of a gas increases

the average particle speed in the gas

will also increase

again as the temperature of the gas

increases the average kinetic energy of

the particles

inside the gas will also increase and

finally as the temperature of the gas

increases

the distribution or spread of the

particle speeds in the gas will also

increase

you'll have you'll have a bigger

difference between the fastest moving

particles in the gas

and the slowest moving particles in the

gas now to consider this idea of

temperature

we've got to consider what what scale

temperature is measured at

now the most common example in the

united kingdom

is the celsius scale which was

established by giving

the temperature at which water becomes

ice a value of 0 degrees celsius

and the temperature in which it boils at

a value of 100 degrees celsius

now using these fixed points the celsius

scale was created

so the celsius scale depends on the

properties of a substance that we've

chosen for our convenience

water it's not very scientific it's not

very absolute

if water was not the most common

substance on earth

there'll be no logical reason for

choosing this to base our temperature

scale

on which is why we've got to use a more

absolute scale of temperature

which is the concept of kelvin and this

is why measuring temperature in kelvin

is vital in thermal physics

so just to recap to produce any

temperature scale

you've got to use at least two fixed

points to make a range of the scale

so the common example is the celsius

scale the celsius scale is based on the

properties of water

so a thermometer is placed in water when

it's at freezing point

and we define this as zero degrees

celsius the thermometer is then placed

in water when it's a boiling point

and we define that at 100 degrees

celsius so we've got our boiling point

and freezing point so this sets the

scale of the temperature

so we say one is at zero and one is at a

hundred

so the space in between these points is

then divided into 100

parts to get one degree now this is a

completely

non-scientific and non-fundamental way

to set a scale

so therefore it's a bit of an abstract

scale so all temperature scales which

are not kelvin do not have a basis in

fundamental science

now the method used to derive the kelvin

scale was

actually derived from fundamental

properties of gus

so in 1848 william thompson who was

later honored by queen victoria and

called law kelvin

came up with the kelvin scale for

temperature so he measured the pressure

caused by gases at

known temperatures and plotted the

results and for every

every gas he found a graph like this one

now by

extrapolating his results he found a

temperature in which a gas

in theory would exert zero pressure you

can see the points which he's taken

experimentally with the dots

and the blue line and the extrapolation

back to when it would exert

zero pressure now it's important to note

that for this extrapolation

we're assuming that the laws of physics

are constant at all temperatures

which thankfully is true but kelvin what

didn't realize this

now since pressure is caused by the

collisions of the gas particles with the

container

zero pressure means the particles are

not moving and therefore have

no kinetic energy so when the particles

exert no pressure

with the particles have stopped moving

completely and we call this temperature

absolute zero it's not possible to get

any colder

now on the celsius scale this

temperature is minus 273 degrees celsius

now this temperature has never actually

been reached by scientists currently

however it's hypothesized to be the

lowest temperature possible in our

universe

so this value of minus 273 degrees

celsius

is called absolute zero because it's the

lowest temperature possible

now as the kelvin scale of temperature

is absolute

absolute zero is zero degrees kelvin now

in the kelvin scale

the energy of the particle is

proportional to the temperature of the

substance it is part of

so at absolute zero the particles of the

substance are

stationary because they have no kinetic

energy

now in this definition we are ignoring

movement due to quantum mechanical

effects

so actually a better definition of

absolute zero

is when we say the internal energy of a

substance

is only potential energy because the

kinetic energy store

is zero so the absolute zero is when the

internal energy of a substance is at its

minimum

now just to clarify one kelvin is the

same size as one degree celsius

but the kelvin scale starts at absolute

zero

so to get into your degree celsius from

kelvin

you would do the kelvin minus 273

whilst getting kelvin from degrees

celsius you would do

degrees celsius plus 273 equals your

value in kelvin

now this is verified as the line between

temperature and gas pressure

always cuts the temperature axis at

minus 273 degrees celsius

regardless of the gas used or the amount

of gas you use it always cuts at the

same point

now in the previous statement we talked

about internal energy

now in the particle model we should

consider all forms of energy stored in a

particle structure

now as well as the average kinetic

energy of a substance which links to the

temperature

there is also a potential energy stored

in the substance due to the forces of

attraction between the particles in the

substance

so there's a potential energy store

between the particles in the substance

which is due to the intermolecular

forces of attraction between the

particles

and there's also the previously

mentioned kinetic energy store found in

the particles of the substance

due to the particles moving now in the

particle structure you've got these two

energy stores the kinetic energy store

and the potential energy store

now we refer to these together as the

internal energy of the substance

so the internal energy is equal to the

kinetic energy store

plus the potential energy stored but

it's important to note

that it has to be for all of the

particles in the substance

so the internal energy of matter is

equal to the kinetic energy of all

particles

plus the potential energy of all

particles so to summarize these ideas

the particles within a substance all

possess kinetic energy which is due to

their random motion

the particles also contain potential

energy due to the chemical bonds and

intermolecular forces of attraction

holding them together and the bonds

within their nuclei

the sum of all these kinetic and

potential energies found in each

particle

represents the body's internal energy so

it is equal to the kinetic energy store

plus the potential energy store

now changing either the kinetic energy

or the potential energy

causes the internal energy to change now

the formal definition

of us of internal energy of a substance

is that the internal

energy of an object is the sum of the

random distribution of the kinetic and

potential energies of its molecules

so increasing either the potential or

the kinetic energy store or both

will result in an increase in internal

energy

now it's important to note that the

internal energy store

is a combination of the potential and

the kinetic energy stores

and these stores are internal to the

system they're not combined with

external stores so don't confuse the

kinetic energy

of the particles with the kinetic energy

of the object itself

moving now it's important to note

that changing kinetic energy changes the

internal energy store

now change in the kinetic energy occurs

when the temperature of the substance

changes now by that same token change in

the potential energy store

changes the internal energy store of the

substance

which occurs when the object changes

state so this leads to a fundamental law

of physics

that the change in internal energy of

the object

is the total energy transfer due to work

done on the object

and heating so work done is placing

energy into the system to change either

the potential or the kinetic energies

which is what we call the first law of

thermodynamics

now when applied to objects the

direction of the energy transfer is very

important

as it determines whether the internal

energy of your object goes

up or down so energy can be changed

between particles

in a substance now if a substance is not

heated

or cooled it acts as a closed system now

a closed system is one where there's

no transfer of matter or energy in or

out of that defined system in this case

the substance itself so this means the

substance has

a constant internal energy now in this

concept

energy is constantly transferred between

the particles within a system

through collisions between the particles

however the total combined energy of the

particles

remains unchanged so you've still got

that constant internal energy

now the energy of an individual particle

can change in the system with each

collision

but the total internal energy of the

system remains unchanged

so this leads to an important

consequence of thermodynamics

the average speed of the particle will

stay the same

provided the temperature of the closed

system stays the same

and no work is done on the system but

the

internal energy can be increased by

heating it

or doing work into the system to

transfer energy

into the system eg by changing its shape

this will cause the average speed of the

particles to increase

now by the same effect internal energy

can be reduced by

cooling the system or by doing work to

remove

energy from the system now the average

kinetic energy

and or potential energy of the particles

will decrease as a result of

energy being transferred out of the

system

so for example when a substance changes

state

it can change the amount of internal

energy in its structure

as you can see here when you've got it

when you've got ice

water and steam and you can see that the

internal energy of the substance is

changing

as it's changing state now it's

important to note that work

can be done in two ways to a system

firstly work can be done to change the

kinetic energy store of a material which

will change its temperature

this physics is covered by something

called specific heat capacity

and work can be also done to change the

potential energy store of material

changing its state this physics is

covered by the latent heat

and will cover these concepts in the

next lesson on the course

so let's summarize what we've looked at

in today's lesson

internal energy is the sum of the

randomly distributed kinetic and

potential energies of the particles in a

body

the internal energy of a system is

increased when energy is transferred to

it by heating

or when work is done on it or vice and

vice versa

so we've got the idea of the first law

of thermodynamics

we've also got an appreciation that

during a change of state the potential

energies of the particles

are changing but not the kinetic

energies so if we've been successful and

learnt in today's lesson

we feel to describe what the difference

is between heat and temperature

link the ideas of internal energy to

potential kinetic energy

and use these equations to calculate

internal energy

so thank you very much for watching

today's lesson on an introduction to

thermal physics

which is part of the thermal physics

topic in aqa a level physics

thank you very much for watching and

have a lovely day