hey it's Kalei in this lesson we're going to learn to measure to the half
centimeter in our lesson so far we have been measuring the lengths and heights
of objects to the whole centimeter like this red line which is 18-hole
centimeters long but we know that our line could be just a little longer and
then would have a length somewhere between 18 and 19 centimeters let's look
at what a centimeter really is here I've zoomed in on our ruler do you see all
the little lines between the zero centimeter mark and the one centimeter
mark how many spaces are there in one centimeter we can count them one two
three four five six seven eight nine ten these little marks are called
millimeters there are ten millimeters in every one centimeter millimeters are
used to measure really tiny things but today we're going to focus on things
that are bigger than a millimeter just like we've found we can break an inch
into parts we're going to break our centimeter into parts so here are my
centimeter ruler I have a rectangle that is exactly one whole centimeter but I'm
not going to break it into ten parts so the centimeters are already very small
I'm only gonna break it into two parts remember we measured our blue rectangle
to be exactly one whole centimeter now if I draw a line right down the middle
of the rectangle what do we get well now we have two rectangles that are each
half a centimeter long so we see that we can divide a centimeter into two equal
parts that are each half a centimeter long so if I get a ruler here I can see
where the numbers represent my whole centimeter length but there are these
lines here in between the whole centimeter marks what do you think those
represent yeah those are the half centimeter marks
now let's use this ruler to find some measurements what is the length of this
rectangle it goes past the 5 centimeter mark and the little marker in between 5
and 6 centimeters so that tells me it is five and a half centimeters long let's
do another this one is longer I see that it starts at 0 centimeters and it
stretches all the way past the 10 centimeter mark the end is at the
halfway mark so this rectangle is 10 and 1/2 centimeters long let's do a word
problem John and Kayla shared a chocolate bar how long was the chocolate
bar before they split it so I think we will need to measure each of the pieces
and then add those measurements together let's measure John's first so if we line
up John's chocolate on the ruler it looks like it comes out to one and a
half centimeters long so we can write that down and now we can measure cut
Kayla's chocolate and her bar is four whole centimeters so we can write that
down two and now we can add those lengths together one and a half
centimeters plus 4 centimeters is five and a half centimeters so the original
chocolate bar was five and a half centimeters long let's take a zoomed-in
look at our centimeter ruler again let's look between the one centimeter and the
two centimeter marks remember we have all those little lines that represent
the millimeters but notice that this line is longer that is the halfway mark
between one and two centimeters so using the marks on our ruler how long is the
red rectangle it passes the three centimeter mark and lands right at that
longer middle line so this rectangle is three and a half centimeters long great
job breaking centimeters up into holes and half
practice which you've learned by doing the online games and quizzes have fun
and remember to always be clever