Tip:
Highlight text to annotate it
X
Welcome to lab 8.
In this lab we will explore bouyancy. You already know that things underwater seem lighter
than normal. We will look at why in just a minute. First, let's look at density.
Density is just the mass per volume of an object. Water, for example, has a density
of 1 gram per cubic centimeter. Steel, on the other hand, has a density of nearly 8
grams per cubic centimeter. We'll need to be able to convert a volume into a mass, and
visa versa, so density will allow us to do that.
Here's a simple explination of why objects seem to be lighter under water.
Here we have some water. If we look at a little volume of water inside this tank, it doesn't
sink or float; it's just water like the rest of the water. If, however, we remove the water
from the tank, we know it has a has a downward force on it from gravity. So, it must have
had that force cancelled by the rest of the water when it was in the tank. So, if we put
in anything else, such as a void, the liquid must still be exerting a force equal to the
displaced water.
Make sure you are comfortable with calipers before starting this lab.
Let's look at how we will see this.
You'll want to attach a string to the bottom of your scales. Remember torque? You need
to attach it directly under the plate; along the other bar will make your measurements
all too light.
Use your grey box to measure masses hanging in the water. You'll be comparing the real
mass (out of water) with the apperent mass. The mass does not change, but appears to be
less because of the water mass displaced. Make sure the mass you are measuring is fully
submerged. Carefully measure the volumes of the objects with calipers.
You'll be comparing the caliper measured volume with the scale and archemidies measured volume,
and will come up with densities from the volumes too; you'll compare these with literature
(that is the lab manual in this case).
The second experiment will have you adding salt to a measured amount of water, in predefined
concentrations, and measureing the apparent masses. Make sure you accound for the weight
of the paper if you use paper to hold the salt on the scale. Stir well! You'll get the
solution densities from this. You'll also be given an unknown density salt solution,
and you'll use a graph of your data to find this.