Temperature & Thermal Energy

D. Crowley, 2008

Temperature & Thermal Energy

• To understand the difference between temperature and thermal energy

Cold Tea

• In pairs you need to come up with an explanation as to why a cup of tea goes cold when it is left out…

• A cup of hot tea has heat energy, in the form of kinetic energy from its particles (which are moving around a great deal)

• If this tea is left for long enough them this kinetic energy is transferred from the hot tea to the surroundings

• Heat is transferred is there is a temperature difference (between the tea and the surroundings), and the hot tea transfers this energy via conduction (vibrating particles in solids), convection (movement of liquid / gas particles from hot to cold) and radiation (all objects above absolute freezing radiate heat to the surroundings)

Boiling Water & Sparkler

• Look at the small beaker of water boiling and the home-made sparkler (a damp splint with Magnesium on it)

• Which of the two has the greater temperature? Does this mean it has the same thermal energy?

Boiling Water & Sparkler

• Although the sparkler is at a much greater temperature (>2000oC) than the boiling water (100oC) it contains less thermal energy as it is much smaller

• The water is a lower temperature, but as it has a bigger volume than the sparks of the sparkler it stores more thermal energy (heat)

* This is also why a spark from a sparkler will not necessarily burn you if it falls on your hand, as although it has a very high temperature the thermal energy it has is very small (as the spark is very small)

Heat

• Heat and temperature are very different things

• Heat is a form of energy (measured in J)

• Temperature is simply a measurement of this energy (measured in oC)

• For example, a swimming pool at 30°C is at a lower temperature than a cup of tea at 80°C

• However the swimming pool contains more water, so it stores more thermal energy or heat than the cup of tea

Particle Model

• Imagine a beaker of water and swimming pool both at the same temperature of 50oC

• Which one contains more thermal energy?

• Draw a particle model of beaker and swimming pool…

Particle Model

• The swimming pool has more thermal energy than the beaker, as it is so much larger

Beaker of water Swimming pool

• Although the temperatures are the same (measurement of the heat energy) as there are so many more particles in the swimming pool the thermal energy (heat) carried by it is much greater

Temperature vs Heat

• Complete the temperature vs heat worksheet

Temperature vs Heat