Measurements of time. We’re going to look
at the dimensions and the units of that. Now, dimension of time
just represents any type of measurement of
any physical property that we’re talking
about the time. Could be a location. It could be a span. It’s got the same basic
dimension for both of those. And our generic notation
for the dimension of time is a capital T,
or some textbooks put the square
parentheses around there. Now, let’s take a look at
this location and span, and see a little bit more about
what we mean by these things. For location and
time, we’re describing when something happens. So that’s one of the
relative to a fixed reference system. And this is what we
often refer to when we say, when did it happen. We want to know what time,
what day, what year, et cetera. But we could also refer to
it relative to the start of an event. So if we’re dealing
with a physics problem, you might say, well, when
did it hit the ground. Three seconds after
it was dropped. So we can describe that
location in time relative to the start of a
particular event. Then we get to time spans,
how long something lasts. And when we say something,
we mean an event. So we could be talking
about the class, we could be talking
about a particular video. And how long does that last? Remember that our time span
doesn’t tell us exactly when it started and stopped. So a five-second time span
could be from the start at zero to five seconds, but a
five-second time span could also be from two
seconds to seven seconds. Both of those
cases, five seconds elapsed between the
start and the end. Now, when we’re recording
all these values, make sure you include
units with the values. Particularly with
our time spans, we need to know what