Archimedes

1
Archimedes Principle

• An object that is submerged in a liquid will
  experience an additional upward force (due to the
  submersion) that is equal to the weight of the
  amount of liquid that was displaced by the
  object. This force is often called the buoyant
  force.

2
Example
A metal ball of volume 50cm3 fully submerged in
water will experience a buoyant force of
mass of displaced water
density of water
volume of ball
3
Free Body Diagram (3 forces)
string
density of water
T
volume of ball
density of metal
4
Q1 Using Newtons Second Law

• In this situation a0, therefore

?
?
?
? By measuring T and V, and knowing the density
of water and the acceleration of gravity, the
density of the metal can be calculated.
5
Titanics Force Diagram
Volume(buoyancy)
6
Activity I Measure T for different size spheres
(different radii) and determine the
density of the spheres.
1. Radii, not diameters ! You probably need to
divide by 2.
2. Give me this difference as uncertainty.
measured
calculated
measured
What is the slope? Get rm from slope.
plot
7
Equipment

• Force sensor
• Metal tray (place metal balls into tray)
• Glass cylinder filled with water.

Only fill water into glass cylinders never any
other type of liquid!!!!!!!!!!!!!
8
When to push the Tare button?
What do you measure in this activity (once the
tray with ball hang on the force sensor and are
submerged in water) if you push the Tare button

• before you even hang the tray on the force
  sensor?
• Wtray Wball Fbuoyant(ball)- Fbuoyant(tray)
• after you hang the tray into the water but
  without the sphere on it.
• ? Wball Fbuoyant(ball)
• The second method measures T as defined before ?
  T versus r3 plot
• should go through the origin.

9
Using Other Types of Fluids
Activity II Determine the density of the fluid
using a submerged metal mass (made of steel,
density given).
Isopropyl Alcohol (70)
Metal mass
Tap Water
(You can use a force sensor to measure mg.)
Corn Syrup
Salt Water
Do these measurements in the plastic beakers. Do
not pour these fluids into the tall glass
cylinder!!! You dont need a metal basket here.
Do not pour isopropyl alcohol, salt water, or
corn syrup into the drain! We reuse these liquids
(and it is illegal to pour isopropyl alcohol into
the drain). Leave them in the plastic beakers and
cover them with the round cardboard when you are
done.
10
Measuring the Fluid DensityAgain
Activity III Determine the density of the fluid
again (as a comparison) using a mass scale and
measuring the volume of the fluid.
11
Please..

• Remember not to pour anything but plain water
  into the tall glass cylinders
• Do not pour alcohol, corn syrup or salt water
  into the drain.
• Clean up any spills immediately. Corn syrup dries
  and becomes hard to remove from tables etc
• Clean your table with a sponge or paper towel
  before you leave.
• Cover the liquids in the plastic beakers with
  round cardboard before you leave.