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Distinguishing between the average kinetic energy of particles and the total energy within a system.
Why can a tiny spark from a sparkler at land on your skin without a major burn, while a cup of coffee at only would cause a serious injury?
In physics, temperature is a measure of the average kinetic energy of the particles in a substance. Think of it as the 'intensity' of the heat. When you heat up a gas, the molecules zip around faster. If you measure the speed of just one molecule, it might be slow or fast, but the temperature tells us the average. It does not depend on how much of the substance you have. A drop of boiling water and a pot of boiling water are both at because their molecules are moving at the same average speed.
Quick Check
If you have a small cup of water and a large bucket of water both at , which one has molecules with a higher average kinetic energy?
Answer
They are the same; temperature measures the average kinetic energy, which is identical for both.
Thermal energy (or internal energy) is the total energy of all the particles in an object. Unlike temperature, thermal energy does depend on mass. To calculate the total, you add up the kinetic energy of every single atom. This is why a giant iceberg actually contains more thermal energy than a cup of boiling coffee. Even though the iceberg's molecules move slowly (low temperature), there are trillions more of them, so their combined energy is much higher. Heat is the transfer of this energy from a warmer object to a cooler one.
1. A spark from a handheld sparkler is roughly . 2. A warm bathtub is roughly . 3. The spark has a much higher temperature (average speed). 4. However, the bathtub has vastly more thermal energy because it contains billions of times more water molecules than the tiny spark.
To find the Kelvin temperature of a room that is : 1. Use the formula . 2. Substitute the Celsius value: . 3. Result: .
Quick Check
What is the Celsius equivalent of Absolute Zero ()?
Answer
If Object A is of iron at and Object B is of iron at : 1. Their temperatures are equal (). 2. Their average kinetic energy per molecule is equal. 3. Object B has exactly twice the thermal energy of Object A because it has twice the number of vibrating atoms.
Which of the following describes temperature?
If you double the mass of a substance but keep its temperature the same, what happens to the thermal energy?
It is possible to have a temperature of .
Review Tomorrow
Tomorrow morning, try to explain to a friend why a giant glacier has more energy than a hot cup of tea, even though the tea is 'hotter'.
Practice Activity
Look at a weather report in Celsius and practice converting the high and low temperatures into Kelvin by adding 273.