Introduction to Physics Notes

• Physics is the study of the fundamental laws of nature, which are the laws that underlie all physical phenomena in the universe.
• These laws can be expressed in terms of mathematical formulas, which relate various measurable quantities.
• Physicists make precise, quantitative comparisons between the predictions of theory- derived from the mathematical form of the laws- and the observation of experiments. Advances in physics, then, depend on the comparisons between theory and experimental work.

Dimensions and Units

• To make quantitative comparisons between the theories of physics and physical experiments, certain basic physical quantities must be measured. The standards accepted for measuring any quantity are called units. We refer to the type of quantity being measured as its dimension, regardless of the units used in its measurement (ex: distance).
• The three most basic qualities, or dimensions, we will measure are length (L), mass (M), and time (T). In fact, these three quantities (and combinations of them) will be the only quantities we consider in the first third of the course, which is referred to as “classical mechanics” or “Newtonian Mechanics”.

\ Later in the course, other fundamental quantities, such as temperature and electric current, will be introduced. The seven fundamental SI units, along with the quantities they measure are:

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• The Meter: 1 m = the distance traveled by light in a vacuum in 1/299792458th of a second (defined based on speed of light).
• The Second: 1 s = the time 9192631770 vibrations of cesium-133 atoms placed under certain conditions (defined based on the vibrations of a cesium-133 atom).
• The Kilogram: 1 kg = the mass instead of being based upon a shiny hunk of metal stored in a vault in Sevres, France, on the outskirts of Paris, the kg is now based on Planck’s constant- a tiny unvarying number that plays a key role in quantum physics.

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