Ditujukan untuk meningkatkan kualitas proses dan hasil perkuliahan Fisika di tingkat Universitas
1: Units, Dimensions, and Scaling Arguments
I'm Walter Lewin. I will be your lecturer this term. In physics, we explore the very small to the very large. The very small is a small fraction of a proton and the very large is the universe itself. They span 45 orders of magnitude--
a 1 with 45 zeroes.
To express measurements quantitatively we have to introduce units. And we introduce for the unit of length, the meter; for the unit of time, the second; and for the unit of mass, the kilogram. Now, you can read in your book how these are defined and how the definition evolved historically. Now, there are many derived units which we use in our daily life for convenience and some are tailored toward specific fields. We have centimeters, we have millimeters kilometers.
We have inches, feet, miles.
Astronomers even use the astronomical unit which is the mean distance between the Earth and the sun and they use light-years which is the distance that light travels in one year. We have milliseconds, we have microseconds we have days, weeks, hours, centuries, months-- all derived units.
For the mass, we have milligrams, we have pounds we have metric tons.
So lots of derived units exist. Not all of them are very easy to work with. I find it extremely difficult to work with inches and feet. It's an extremely uncivilized system. I don't mean to insult you, but think about it-- 12 inches in a foot, three feet in a yard. Could drive you nuts.
I work almost exclusively decimal, and I hope you will do the same during this course but we may make some exceptions. I will now first show you a movie, which is called The Powers of Ten. It covers 40 orders of magnitude. It was originally conceived by a Dutchman named Kees Boeke in the early '50s. This is the second-generation movie, and you will hear the voice of Professor Morrison, who is a professor at MIT.
The Power of Ten-- 40 Orders of Magnitude. Here we go.
I already introduced, as you see there length, time and mass and we call these the three fundamental quantities in physics. I will give this the symbol capital L for length capital T for time, and capital M for mass.
All other quantities in physics can be derived from these fundamental quantities.
I'll give you an example.
I put a bracket around here. I say [speed] and that means the dimensions of speed. The dimensions of speed is the dimension of length divided by the dimension of time. So I can write for that: [L] divided by [T].
Whether it's meters per second or inches per year that's not what matters. It has the dimension length per time. Volume would have the dimension of length to the power three. Density would have the dimension of mass per unit volume so that means length to the power three.
All-important in our course is acceleration. We will deal a lot with acceleration. Acceleration, as you will see, is length per time squared. The unit is meters per second squared. So you get length divided by time squared.So all other quantities can be derived from these three fundamental. So now that we have agreed on the units--
we have the meter, the second and the kilogram--
we can start making measurements.
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