Heat & Temperature

Concept Summary

Batesville High School Physics

Historical Heat As late as 200 years ago, heat was

regarded as a fluid, called “caloric”. It was believed that this caloric fluid

flows from hot objects to cold objects.

Historical HeatThe scientific study of heat was

motivated by the Industrial Revolution with its use of steam engines and machines.

In the 19th century, James Prescott Joule (and others) showed that heat is a form of energy.

Heat TermsActually, thermal energy is only called

heat when it is moving between objects.

Heat transfers thermal energy from one object to another (like work).

Energy inside an object is properly called internal energy - the kinetic and potential energy of its particles.

Adding HeatSo, when heat energy is transferred to

an object, the energy “shows up” as kinetic energy & potential energy of the object’s particles (atoms, molecules, etc.)

TemperatureAn object’s temperature is related to

the average kinetic energy of the particles in an object.

Higher average KE means higher temperature.

Moving Heat EnergyHeat energy “flows” from an object at

higher temperature to an object at lower temperature - if the objects are in thermal contact.

(To make energy move the other way, you have to do work.)

Thermal EquilibriumHeat energy will “flow” until the two

objects reach the same temperature - they are then in thermal equilibrium.

The Lowest TemperatureSince there is a minimum kinetic energy

for particles (0 J), there is a lowest possible temperature – absolute zero.

Scientists have produced temperatures within a small fraction of a degree of absolute zero.

Temperature Units

Name Water freezes

Room Temp.

Water boils

Absolute Zero

Fahrenheit 32o 70o 212o -459.7o

Celsius 0o 21o 100o -273.15o

Kelvin 273.1 294 373.1 0

Temperature is NOT HeatAn object may have a relatively high

temperature and a relatively low internal energy.

An object may have a relatively low temperature and a relatively high internal energy.

Temperature is NOT Heat It is possible for heat to flow from an

object with very little energy (but high temperature) to an object with lots of energy (but low temperature).

Temperature and HeatWhen you add heat energy to an

object, its temperature may (or may not!) increase.

Measuring Heat EnergySince heat is energy, it can be

measured in Joules.A common (and old-fashioned) unit of

heat energy is the calorie.

The calorie & the Calorie1 calorie is the amount of heat needed

to raise the temperature of water by 1oC.

1 Calorie = 1 kilocalorie = 1000 caloriesThe Calorie is the “diet calorie”.

Specific Heat Capacity1 calorie of heat will raise the

temperature of different substances by different amounts.

The amount of heat energy required to raise the temperature of a substance by 1oC is called the specific heat capacity, or specific heat.

Specific Heat of WaterBy definition, the specific heat of water

is 1.This is a high specific heat, meaning it

takes a relatively large amount of energy to raise the temperature of water – water holds a lot of energy.

Calculating Heat EnergyThe amount of heat energy needed to

raise the temperature of a a substance depends on: The amount of the substance The specific heat of the substance The change in temperature

Calculating Heat EnergyH = mcT

where: H = heat energy added/removed m = mass c = specific heat T = change in temperature

Moving Heat EnergySince heat is energy, heat can be

conserved in an isolated system. In a 2-object system:Heat lost by object A = heat gained by

object BmAcATA = mBCBTB

The End