Hi, in today’s lab, we will be exploring
the principle of buoyancy.
The first of the lab will mostly be reminding
ourselves of
what the buoyancy force feels like.
Most of you have probably experience this
force in the bathtub or in a swimming pool.
In this case, we have given you a big vat
of water and a little plastic container that
you can use as a ship. You can try this at
home, actually.
What we ask you to do is to simply feel the
force for yourself. So you can put your hand
right in there and push it around. And ask
yourself simple qualitative questions like:
What is doing the pushing?
Or which way is it pushing?
Does it matter if I push fast or slowly?
Or if I push near the side or in the middle?
Or if I push tilted, or not?
So just have a little fun with it and put
down some observations for yourself.
From the qualitative description in Part 1,
the handout will guide you through a simple
derivation to reach a more quantitative formula
with which you can do some simple calculation.
In Part 2, we will apply this formula to identify
what tree a certain stick comes from by measuring
its density.
Here we have stick that we picked up, actually,
in the Langara golf course.
You see that we have chosen a section with
a fairly uniform cross-section, and also we’ve
marked out ten roughly equal divisions so
that we can see roughly what percentage of
the stick lies in the water.
So we simply dunk this in the water and we
can see that at a certain submersion level
that it floats and it’s in equilibrium.
And we can also note by the markings, roughly
what percentage of the stick is submerged.
From that we can work out the density and
therefore identify what tree it comes from.
So here the setup for the last part of the
lab.
Once again, like Part 1, we have a big vat
of water, and the round plastic container
for our ship.
This time, though, we will be adding a little
bit of cargo in it in the form of the weight.
And you will see that as we add the weight,
the ship will sink more.
And by using Archimedes principle, we can
find out exactly how much more.
So first, notice the ship without the cargo
the water level and how much it’s sunk.
And then we can add the weight to the boat,
making sure it’s fairly even, and not very
tilted, nice and balanced,
and you can see that it has sunk quite a bit
more as a result of the added weight.
Now to work out exactly how much, it is important
to measure this distance right here from the
bottom of the boat to where it hits the water.
And it is up to you to figure out the best
method how.
For more details you can refer to your handout.
