Heat & thermodynamics: Physics Notes for Engineering Services (ESE)

Heat & Thermodynamics – Beginner Study Notes

(Physics – Engineering Services (ESE))

1. What is Thermodynamics?

Term	Simple idea	Everyday picture
Thermodynamics	The science of heat, temperature, and energy.	Like a coach who tells the body how to move heat around.
Heat	Warmth that moves from a hotter thing to a colder one.	A hot cup of tea cooling on a table.
Temperature	A number that tells how hot or cold something is.	The thermometer in your kitchen.
Energy	The ability to do work or change temperature.	The battery that powers your phone.
System	The part of the world we are looking at.	The kettle you are heating.
Surroundings	Everything else that touches the system.	The air in the kitchen.

Quick test
If you touch a hot stove, heat flows from the stove to you. What is the direction of the flow?
Answer: From hot to cold.

2. Three Ways Heat Moves

Mode	How it works	Everyday example
Conduction	Molecules touch each other and pass energy.	A metal spoon getting hot in soup.
Convection	Hot fluid carries heat to cold fluid.	Warm air rising in a room.
Radiation	Energy travels as waves, no material needed.	Sunlight warming your face.

Tiny analogy
Think of a train:
Conduction = cars touching each other.
Convection = a freight train that carries cargo (heat) up a hill.
Radiation = a train that sends a signal instead of carrying cargo.

3. The First Law – Energy Conservation

Simple statement
Energy can change form, but it never disappears.

Step	What happens	Example
1	You turn on a kettle.	You plug it in.
2	Electric energy → Electrical heat in the kettle.	The kettle’s coil heats up.
3	Heat → Water temperature rises.	Water goes from 20 °C to 100 °C.
4	Some energy leaks out (surroundings).	The kettle’s metal gets warm.

Formula (tiny example)
Q = m × c × ΔT

Q = heat added (Joules)
m = mass (kg)
c = specific heat (J/(kg·°C)) – for water ≈ 4180
ΔT = change in temperature (°C)

Example calculation
Heat 1 kg of water from 20 °C to 80 °C.

ΔT = 80 – 20 = 60 °C
Q = 1 kg × 4180 J/(kg·°C) × 60 °C
Q = 250,800 J

Take‑away
The kettle used about 250 kJ of electric energy to heat the water.

4. The Second Law – Heat Flows Naturally

Simple statement
Heat likes to spread out from hot things to cold things.
You can’t get all the heat in a cold room without using work (like a fridge).

Idea	Everyday picture
Heat flows from hot to cold	Hot soup in a bowl cools when you sit next to it.
You need work to reverse it	A fridge uses electricity to pull heat from inside to outside.

Tiny analogy
Imagine a pile of snow that melts when the sun shines. The snow “spreads” the meltwater out. Trying to keep the water in the pile would need a pump.

5. The Third Law – Absolute Zero

Simple statement
You can’t cool something down to absolute zero (‑273 °C) no matter how hard you try.

Why?	Everyday picture
At absolute zero, atoms stop moving.	A rock in a freezer gets very cold, but never reaches complete stillness.

Quick thought
If you could reach absolute zero, a cup of coffee would never heat up. (Just a fun idea!)

6. Everyday Thermodynamics in a Minute

Situation	What happens?	Why?
Coffee cooling	Coffee temperature drops.	Heat flows from coffee to room air (conduction + convection).
Air‑conditioner	Room becomes cooler.	The AC does work to move heat from inside to outside.
Ice melting	Ice turns into water.	Heat from the room warms the ice (conduction).

7. Quick Reference Cheat Sheet

Concept	Quick phrase	Example
Heat	Warmth that moves	Hot coffee cooling on a table
Temperature	Hotness number	Thermometer reads 30 °C
Energy	Power to change things	Battery powering a phone