Lesson: Hydrostatic Forces

Overview of this Lesson

Hydrostatic forces are important for the design of large engineered systems such as dams.

A type of hydrostatic force, called the buoyant force, is important for
* designing ships, weather balloon, kayaks, subs …
* advanced topics such as bubble dynamics, natural convection, and atmospheric science

What these forces have in common is that they are both due to a hydrostatic pressure distribution acting over an area. Thus, this lesson introduces pressure distributions and how to find the resultant force.

Benefits of this Lesson

  • Understand how force and center of pressure are related to pressure distribution
  • Learn how to calculate the force due to a pressure distribution (flat panel)
  • Learn how to calculate the buoyant force on an object.
  • Learn a step-by-step process for drawing a free body diagram (FBD).

Goals (results we intend to create)

1. FBDs. Learners can
* explain the concepts and the process for drawing a free-body-diagram (FBD)
* sketch and validate a FBD

2. Foundational Concepts. Learners know these concepts:
* pressure distribution (subconcept: center of pressure CP)
* force (subconcepts buoyant force, hydrostatic force, surface force, body force)

3. Seminal Eqns. Learners know:
* Hydrostatic Force Equations (Eqs. 3.23, 3.28)
* Buoyant Force Eqn (Archimedes' equation) (Eq. 3.36) {learners can derive this eqn.}

4. How things work. Learners know "how things work" for the hydrometer.

Plan (steps to reach the goals)

1. Goal Setting.
Recommend: Write down personal goals for this lesson. Ask yourself, what do I want? What are my motivations for studying engineering? Make your goals specific (i.e. measurable) and challenging. For more information, see "how to write goals."

2. Free Body Diagrams (FBDs)_
Learn the process and concepts for drawing a FBD. Learn this so that you explain the process and apply it correctly. I recommend that you practice the process many times as you do problems so that the process becomes your process. A resource to help you is this handout.

3. Foundational concepts. (p. 48-49).
Learn the foundational concepts listed in goal 2. I recommend that you build your own mreac sheets. Resources to help you include the examples of mreacs (see hyperlinks in goals).

4. Hydrostatic Force Eqs. (p. 48 to 52)
a. Learn the hydrostatic force equations (3.23, 3.28). I recommend that you build your own netmad. Hydrostatic Force Equations netmad.
b. Practice doing problems such as 3.54 to 3.70 (posted solns: 3.56, 3.57, 3.58, 3.67, 3.68).

5. Buoyancy Force Equation (Archimedes Equation) (p. 55-56)
a. Learn how to derive the buoyancy equation from memory. I recommend that you create your own documentation and then practice presenting the derivation to people until you have it down solidly. Resources include this video and its accompanying handout.
b. Learn the buoyancy equation (3.36). I recommend that you create your own netmad. A resource to help you is my buoyancy equation netmad.
c. Practice doing problems such as 3.80 to 3.98. (posted solns: 3.80, 3.87, 3.93, 3.95).

6. Hydrometers. (p. 56).
Make sure that you can explain how a hydrometer works. I recommend that you construct "how things work" documentation. Example of this type of documentation.

7. Lesson Review (Reflective Thinking)
a. Assess your learning using this form. Print1 and staple the form to front of your homework. Resource: (How to write an SII).
b. Assess this lesson using this (form).

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