Hello everyone and welcome to the second lecture
in our introduction to forensic science unit.
Congratulations you have made it past the
first one. I am very proud of you. This one
is going to be on the scientific method. I
know you have probably learned this in every
single science class youíve ever been in,
but we want to keep it fresh in your mind
so we are going to review it again. For me,
I have the scientific method broken up into
five steps. Sometimes you will see six or
seven. It doesnít really matter how many
steps that you have, it is the process that
is important and for the most part it is the
same process no matter which version you use.
For me step number one is I am going to observe
the world and Iím going to ask a question
about it. So fall is going to be coming pretty
soon, and I might notice that the trees are
changing colors and I will say to myself ìHey,
I wonder why the trees are changing colors?î
So I have observed and I have asked a question.
After that you might go, well what are some
possible answers to that? HmmÖ and thatís
when you are going to do step number two.
You are going to make a hypothesis. And your
hypothesis is basically what you think the
answer to you question is. It may be right,
it may be wrong. You are going to do an experiment
to find out what that is. SO thatís step
number 3, conduct an experiment. So you do
your experiment and then you get some data
based on your experiment. So step number 4
is you are going to analyze that data and
then once you have taken a look at the data
you are going to try and figure out what it
all means. SoÖ was your hypothesis correctÖwas
it no, so step 5 is youíre going to make
a conclusion. Now when you are setting up
an experiment, you need to keep a couple of
things in mind. The first are variables. All
a variable is, is just something that can
change in an experiment. When we do the experiment
we want to look at one variable at a time.
We do this because we want to make sure that
it is only that one thing we are looking at
thatís causing something to happen. If you
use two, you may not be sure which one caused
the reaction you observed. Now, in an experiment
there is going to be two different variables
that you are going to look at. One is the
independent variable. And this is the one
thing you are testing to see if it is causing
the observation or not. This is the one that
you manipulate. You actually change this one.
This is the one you are going to set at different
levels and things like that. Now the other
one is the dependent variable. Itís called
the dependent variable because it depends
on the independent variable. This is the thing
that changes because of the independent variableÖbecause
of what you are testing. This is the one you
are going to observe or to measure. SO once
you have figured out what your variables are
for the experiment, then you are going to
go ahead and set up your groups. There are
two different types of groups that you can
have for an experiment. The first is the experimental
group and the second is a control group. Now
the experimental group is going to get whatever
you are testing (independent variable). On
the flip side, the control group, will not
get what you are testing. And the control
group is going to act as our comparison. So
for the experimental and the control group,
we want to make sure that we try to keep the
conditions the same for both groups except
for what we are testing, or as close as you
can possibly get them to being the same. And
thatís to make sure that itís only what
you are testing thatís causing the change
or giving us the results that we have. So
you are going to watch a very short demo with
soda cansÖ so letís play that. So we made
some observations about these soda cans and
now we are going to go through how you would
use this in the scientific method procedure.
So I made the observations about the cans.
The diet can was floating and the regular
can of soda sank to the bottom. So immediately,
the first question that comes to my mind is
why did the diet soda float 
and the regular soda sink? Then I am going
to start to think about answers to that question,
which would be my hypothesis. So if you take
a look at the cans of soda, diet soda lists
no sugar and regular soda lists 24 grams which
is quite a lot. So I think it is the sugar
that is causing this change. So for my hypothesis,
Iím going to put that cans 
with more sugar will sink 
down more in the bin. Ok, so that is pretty
specific, I can test this. You want to make
sure that your hypothesis is testable. If
I take cans and I increase the amount of sugar,
I should see that the cans move down in the
water. So now I am going to focus on the groups.
I have got my hypothesis now I am ready to
do the actual experiment. So I am going to
set up two experimental groups. You could
set up more and I am going to set up my control
group. For my experimental groups, these are
the ones that get what I am testing, which
is the amount of sugar. Thatís what I want
to see if it caused the change or not. So,
for my first experimental group I might have
my can letís say filled with a certain amount
of water and it has a higher level of sugar.
Now, you would want to be more specific about
what those numbers are but for right now we
are going to use it as an example. For 
the second experimental group, I might have
the can with the same amount of water plus
a medium sugar amount. And then for the control
group that does not get what I am testing
so this would be a can that does not have
any sugar in it at all. Ok, the cans and the
water we are going to keep the same because
we want to make sure that it is just the sugar
amount that is causing this change and not
any of that other stuffÖany of those other
variables. So we are focusing on one at a
time. So we did our experiment and letís
say we got these results. For my first experimental
groups letís say we had 20mL of water in
these cans, so the water is kept consistent,
but for my first experimental group I wanted
a higher amount of sugar so I chose 10 grams.
I tried this experiment out three times. You
want to do an experiment more than once to
make sure that it wasnít some sort of random
fluke. So when I did that I found that the
distance of the can from the bottom of the
tankÖso when I had the high amount of sugar
the bottom of the can was at the bottom of
the tank so it was zero. For my second experimental
group we said that we wanted a medium amount
of sugar so I chose 5, and if we take a look
at this group it was about half way up the
tank. And then for the control group, when
we had no sugar at all, these cans stayed
towards the top of the tank. So thatís the
data that we got and now we are going to make
a conclusion based of it. So we can see that
the cans that had more sugar, stayed toward
the bottom of the tank, they sunk more, and
the ones with less sugar stayed towards the
top. So I can say that my hypothesis has support.
Yes, if I have more sugar in the can it is
going to sink farther down in the tank. So
my hypothesis has support. Yay! Sometimes
your hypotheses wonít have support. Sometimes
you will find that you were completely off
the mark, and thatís fine. That told you
that it wasnít that thing, now you should
go test a new thing. So it rules out possibilities
for you. So, negative hypotheses for scientists
are just as important as positive ones.
