this is a lab document that helps students;
To connect the words of Archimedes’ Principle to the actual behavior of submerged objects.
To examine the cause of buoyancy, that is the variation in pressure with depth in a fluid.
To use Archimedes’ Principle to determine the density of an unknow...
Name Anna Lena Stein Stthomas
University
School ____________________________________ Date 11122120
-
Archimedes’ Principle
Purpose
To connect the words of Archimedes’ Principle to the actual behavior of submerged objects.
To examine the cause of buoyancy, that is the variation in pressure with depth in a fluid.
To use Archimedes’ Principle to determine the density of an unknown material.
Explore the Apparatus
Virtual Buoyancy Apparatus PENCIL
We’ll use the Buoyancy Apparatus in this lab activity. You can get quick access to help by rolling your mouse over most
objects on the screen.
Figure 1 – The Buoyancy Apparatus
To investigate buoyant forces we need to measure the weight and volume of objects as well as their submerged weight
when fully or partially immersed in a fluid. We’ll use water as our fluid in this lab. We also need to measure the weight and
volume of the fluid displaced. A hanging scale and a digital scale are available for measuring the weights of our objects.
The overflow of water from the tank spills into a graduated cylinder. The volume of this displaced water can be read from the
graduated cylinder; and the weight of the water can be found by weighing the graduated cylinder before and after overflow.
Three simple and three compound objects are available for study. They are composed of cork, aluminum, wood, and two
unknown materials. These objects can be weighed in air and when partially or fully submerged. The hanging scale is raised
and lowered by clicking and dragging it. Both the hanging scale and the graduated cylinder can be read more precisely by
zooming in. The graduated cylinder is emptied by dragging and releasing it above the tank.
You’ll find that some actions that could be done with real apparatus are forbidden. For example, you can’t weigh more than
one object on the digital scale at a time. And you can’t make a mess by lowering an object into the water while the graduated
cylinder is on the digital scale. Another thing that is largely forbidden is dragging the screen when you’re zoomed in. When
you try to move an on-screen object and it doesn’t behave as expected this means that something else needs to be done first.
There aren’t too many choices.
Archimedes’ Principle:
A body wholly or partially immersed in a fluid will experience a buoyant force equal to the weight of the fluid
displaced.
This and many other phrases you’ll hear when studying buoyancy are mostly meaningless without direct experience. So our
exploration of the apparatus will mainly focus on the various situations you’ll encounter and the related terminology. While
we’re at it, our use of submerged in some cases and immersed in others is not meant to suggest two different phenomena.
Both refer to an object fully or partially in a fluid.
The following exploration, down to the Theory section, is not a part of the graded lab. Instead it’s meant to clarify some
concepts and terms that make better sense if you get some practice with them.
1. What’s a “buoyant force” and what exerts it?
Let’s try it with the system in Figure 1. Right (or Ctrl) click and zoom in on the hanging scale. It appears to read zero
initially. This sort of scale is not very precise. Our simulation reflects that level of precision. (Zoom back out.)
Now drag the cork and aluminum compound object and drop it somewhere below the hanger. It should become attached to
the hanger. You should find that it weighs about 4.4 N. Zooming in and estimating a digit we might have 4.41 N. Drag and
drop it on the digital scale and you’ll get 4.41 N. Which scale should you use? We’ll always use the value from the hanging
scale, 4.41 N in this case, unless we have to use the digital scale for a measurement. This will only happen when we need to
weigh the graduated cylinder.
Now for the “(submerged) weight when fully or partially immersed in the water.” Drag the object back to the hanging scale.
Slowly drag the scale downward until the aluminum disk is about half submerged. The scale might read about 3.73 N. This is
a judgment call since the location of the half-way point is uncertain. Let’s use that value in the following discussion. That’s
the “submerged weight.” We’ll use the term W' (“W prime”) to represent the submerged weight.
So its actual weight is 4.41 N and it appears lighter when partially submerged, maybe 3.73 N. It didn’t lose weight. The water
is providing an upward force on the bottom of the disk. So we would say that a 4.41-N object was buoyed up by a force Fb so
that it appears to weigh, or has a submerged weight of, 3.73 N. Since it’s in vertical equilibrium, we can say ΣFy = 0.
Let’s look at the forces and draw vector arrows to represent each force.
VPL Lab – Archimedes. Buoyancy 2 Rev 12/19/18
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