ENGR& 111
Introduction to Engineering 1: Modeling and Analysis
Everett Community College
Pressure
In-Class Activity 6
Reading: Section 8.6 – Pressure
Learning Outcomes:
The goal of this exercise is to help students learn about pressure and be able to use pressure readings to
do simple calculations.
Background:


SI Units:

AES Units:
(
)
.
Note: psi stands for Pounds per square inch
Absolute Pressure – Absolute pressure uses a perfect vacuum as a reference point. The pressure on
earth is much greater than in a perfect vacuum due to the weight of the Earth’s Atmosphere above
us. The absolute pressure on the Earth’s surface is 1 atmosphere (atm). 1 atm ≈ 14.7 psi ≈ 101 kPa.
Gauge Pressure – Gauge pressure uses the local atmospheric pressure as a reference point. This is
the pressure above or below the local atmospheric pressure. This is typically the pressure you
would see using a tire gauge for your bike or car.
Mini Lab 1:
We are going to perform a simple experiment to see the effects of the atmospheric pressure all around
us.
Materials: Step 1:
Step 2:
Step 3:
Step 4:
At least one empty aluminum can
Gas burner
Set of tongs
Cold Water Bath
Fill the aluminum can with a small amount of water (around 2-4 tablespoons).
Place your can on the burner and heat it until you can see steam coming out of the top
Boil the water for about 30 seconds until steam is quickly escaping from the can. Make
sure not to let it dry up.
In one smooth motion, using the tongs; lift your can off the burner and place it topdown in the cold water bath. Be careful not to spill boil water on desks or people.
You may repeat the experiment if you have additional cans available.
Question 1:
What happened? Discuss this with your team. Using the fact that steam occupies about
1600 times the volume of an equal mass of liquid water, provide a detailed explanation of what
happened to the can and why, in terms of pressure.
1
ENGR& 111
Introduction to Engineering 1: Modeling and Analysis
Everett Community College
Mini Lab 2: Force and Pressure
Your instructor will use a simple Pneumatic Jack and a text book to explore the relationship
between force and pressure.
Your task is to answer the following questions:
Question 2:
How much force must be applied to the handle of the jack to lift up one side of your car
using the supplied hydraulic jack?
Question 3:
What is the gauge pressure of the hydraulic fluid inside the jack when the car is sitting
on it? What is the absolute pressure?
Tips:







If nobody in your group owns a car, just pick a model that you are interested in.
Google the “Curb Weight” of your chosen car
Assume that you will be lifting half of the weight or your chosen car by jacking up one
side.
The geometry of the handle gives you a mechanical advantage of 6.65. In other words
any force, F, applied to the handle results in a force of 6.65*F on the pump cylinder.
Measure the diameters of the small and big cylinders (labeled as “Pump” and “Ram” in
the diagram below) of the supplied Jack using calipers
Convert units as necessary
Show all calculations clearly including units
Here is a cut-away diagram of a similar jack.
2