Physics -- 1.3: Physics is a Science of Measurement
What is our next question?
"What should we observe in nature?"
What do we need to do to be precise in the observation of nature?
All physical quantities that are observed should be measured and described by numbers.
Thought experiment
An experiment that we can think through, rather than actually perform.
What can we conclude about the specific observation of nature seen in the thought experiment?
Describing something as "hot" or "cold" is not very accurate; unless we can say numerically how hot or cold something is, our observation is incomplete.
What is William Thomson's name referred to today?
Lord Kelvin
Who stated the importance of numerical measurements?
Scottish physicist William Thomson
What is a prominent example of the need for quantitative measurements?
The thought experiment on water, beakers, and temperature
In the temperature thought experiment, what materials are presented?
Three beakers: one contains several ice cubes in water (beaker 1), one contains boiling water (beaker 3); one contains a mixture of boiling and iced water (beaker 2)
What would we do in practice to measure the temperatures of the beakers in the thought experiment?
Use a thermometer to measure the temperature of the contents of each beaker and read the hotness or coldness of each beaker.
What must we do in order to study the entire physical world?
We must first observe it
If we used a thermometer to carry out our experiment, what would have happened?
We would now have assigned a number to our observation of nature and would thus have made a precise statement about that observation.
What happens after you complete the thought experiment?
You have contradictory conclusions; the middle beaker is either hot or cold depending on the measurements' sequence.
In the thought experiment, what happens if you put your hand into beaker 1 and then beaker 2?
You will find the first beaker cold, and the second hot in comparison, naturally concluding that it is hot.
In the thought experiment, what happens if you put your hand into beaker 3 and then beaker 2?
You will find the third beaker hot, and the second cold in comparison, naturally concluding that it is cold.