Heat Energy Transfers
Chapter 18
[Recommended Reading : Science Checkpoint Book : 3 ]
What is Heat?
The Basics
Real-Life Example
Heat is the total internal kinetic
A giant swimming pool at 30°C has
energy of atoms and molecules in
much more total heat energy than
a substance. The more mass a
a cup of tea at 100°C because it has
substance has, the more heat
millions more moving molecules!
energy it can hold.
Units: Joules (J)
Temperature vs. Heat
Temperature
Heat Energy
A measure of the average kinetic energy of particles (how
The total kinetic energy of all particles combined
fast they're moving on average)
Units: Joules (J)
Units: °C or K
We measure temperature with a thermometer. When it touches something hot, particles transfer energy to the thermometer,
making the liquid inside expand.
Energy Calculation Formula
Q = m × c × ΔT
01
02
m = Mass
c = Specific Heat Capacity
ΔT = Change in Temperature
Measured in kilograms (kg)
How hard it is to heat the material
Measured in degrees Celsius (°C)
(J/kg°C). For water: 4,200 J/kg°C
03
Example Calculation
Problem
How much energy is needed to heat 2 kg of water by 10°C?
1
2
3
Step 1
Step 2
Step 3
Identify values: m = 2 kg, c = 4,200
Apply formula: Q = 2 × 4,200 × 10
Calculate: Q = 84,000 J
J/kg°C, ΔT = 10°C
Answer: 84,000 Joules of energy needed
How Heat Moves: Conduction
The Process
Heat energy passes from one particle to the next in solids. When heated, particles
vibrate more vigorously and transfer kinetic energy to neighboring particles.
Key Points
Fastest in metals (free electrons help transfer energy)
Occurs in solids, less in liquids, hardly in gases
Cannot occur in a vacuum
How Heat Moves: Convection
The Process
Heat energy is carried away by particles changing position. Warm
fluid rises, cool fluid moves in to replace it, creating convection
currents.
Where It Occurs
Only in liquids and gases where particles are free to move. Cannot
occur in solids or vacuum.
How Heat Moves: Radiation
Electromagnetic Waves
Energy travels through air or vacuum as infrared waves. No particles needed!
Examples
Feeling warmth from the Sun
Heat from a campfire
Greenhouse effect (trapped infrared)
Quick Check!
True or False?
A small spark from a fire has a higher temperature than a radiator, but the
radiator has more heat energy.
Answer: TRUE!
The spark's particles move faster (higher temperature), but the
radiator has way more particles in total, meaning more total heat
energy.
Key Takeaways
Heat vs. Temperature
Mass Matters
Heat is total energy (Joules); temperature is average
Larger mass = more heat energy capacity
energy (°C)
Three Transfer Methods
Energy Formula
Conduction (solids), convection (fluids), radiation
Q = m × c × ΔT for calculations
(waves)