Physics Lab 1.8
Simple Manometer
Manometers are simple
and accurate instruments that are used extensively for
measuring pressures. In this activity, we use a simple
manometer to measure the maximum pressure that a person
can generate using their breath.
Set up the equipment
illustrated in the video lesson and carry out the
experiments described.
Record the results of the
experiment in the table provided and carry out the
calculations needed to complete the table.
Question:
If water with a density of 1000 kg/m3 is used
in the manometer indicated below, what pressure
difference is it indicating. (The difference in height of
fluid in the two legs is 50 cm.) .
Answer
Pressure = 1000 kg/m3
x 9.81 N/kg x 0.5 m = 4905 N/m2 (or Pa.)
Experiment
1.8.1 Simple Manometer
The purpose of this activity is to construct a simple
manometer and use the device to measure pressures.
Materials and Equipment
- A board roughly 1.5 m
x 0.3 m.
- Plastic tubing –
3 to 4 meters.
- Small quantities of
food coloring and dishwashing liquid.
- Tape measure – 1.5
m
- Balloon
Procedure
- Mount the tubing as
illustrated in the video lesson.
- Place a small
quantity of food coloring and a few drops of
dishwashing liquid in a cup of water and draw
this solution into the manometer tube. Fill the
tube with this solution. If any large bubbles
form in the tube, tap the tube to dislodge the
bubbles or empty the tube and start again.
- Blow about 30% to 40%
of the solution out of the tube. Release the
pressure on the manometer and check that the
liquid levels are the same on both sides of the
manometer. (If not, a bubble is blocking one of
the sides of the tube.)
- Now apply a pressure
to one of the pipe ends and measure the
difference in height between the liquid levels in
the two legs of the manometer. Pressure should be
applied to one end of the manometer and the other
end should be open to the atmosphere. There must
be no blockages or hindrances to flow at the open
end of the manometer.
Calculations
The pressure indicated by the manometer is calculated
from the formula for pressure at the bottom of a column
of liquid.
Pressure
= r gh
Where:
r is the density of the fluid in the
manometer (kg/m3)
g is the
gravitational field vector (9.81 N/kg)
h is the difference
in height of fluid between the two legs of the
manometer (in meters)
For Example:
Experiments:
- Use the manometer to
measure the maximum pressure that a person can
generate from his or her breath
- Blow up a balloon and
measure the pressure inside the balloon.
- Allow the air in the
balloon to escape slowly. Monitor the change in
pressure as the air escapes.
Results
- Record the density of
the liquid in the manometer.
The density of water can be regarded as 1000 kg/m3
- List the measurements
taken for the various experiments in the table
below and calculate the pressures indicated by
these readings.
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