Show Advanced Search


Containing Text
- - -
Filter by author or institution
Filter by publication date
October, 2006
Filter by journal section

Filter by science education

Atmospheric Pressure: The pressure at any point in an atmosphere due solely to the weight of the atmospheric gases above the point concerned.

What is Weather?

JoVE 10946

Weather refers to the current state of atmospheric conditions at a specific time and place. Weather is temporary and is influenced by the interactions between the sun, atmosphere (gases around the Earth), hydrosphere (the water bodies of the Earth), and geosphere (the land portion of the Earth). As all of these factors differ across location and time, different weather can be observed across the planet. Solar radiation penetrates the atmosphere to interact with surface water and land masses. These surfaces emit the energy as thermal radiation, or heat, warming the air. Heat either escapes through the atmosphere back into space or is trapped in the atmosphere by specific atmospheric gases—continuously warming the planet. This retention of heat in the atmosphere is called the greenhouse effect. So-called greenhouse gases retain more heat than other gases. Warm air is less dense than cold air, so warm air rises. Rising air creates vertical currents into the upper atmosphere, which has lower atmospheric pressure. As the air gets further away from the source of thermal radiation, it begins to cool, becomes denser, and falls again. This process is known as convection circulation. Weather is typically measured by six parameters: temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness. Meteorologists measure these conditi

 Core: Biological Diversity

Piping Networks and Pressure Losses

JoVE 10389

Source: Alexander S Rattner, Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA

This experiment introduces the measurement and modeling of pressure losses in piping networks and internal flow systems. In such systems, frictional flow resistance from channel walls, fittings, and…

 Mechanical Engineering


JoVE 10882

The process of breathing, inhaling and exhaling, involves the coordinated movement of the chest wall, the lungs, and the muscles that move them. Two muscle groups with important roles in breathing are the diaphragm, located directly below the lungs, and the intercostal muscles, which lie between the ribs. When the diaphragm contracts, it moves downward, increasing the volume of the thoracic cavity and creating more room for the lungs to expand. When the intercostal muscles contract, the ribs move upward and the rib cage expands, similarly expanding the thoracic cavity. Each lung is surrounded by two membranes called plurae, which are separated by fluid. This fluid creates an adhesive force that causes the lungs to stretch as the thoracic cavity expands. The increased volume in the lungs reduces the pressure. When the pressure drops below atmospheric pressure, this produces a pressure gradient that moves air from the higher-pressure atmosphere into the lower-pressure lungs. When the diaphragm and intercostal muscles relax, the volume of the lungs decreases, increasing the pressure in the lungs. As pressure increases beyond atmospheric pressure, the resulting pressure gradient pushes air out of the body. In this way, the cycle of inhaling and exhaling is maintained. Boyle’s law states that, at a given temperature in a closed space, the press

 Core: Circulatory and Pulmonary Systems


JoVE 10675

Vaporization changes a liquid substance into a gaseous or vaporous substance. To achieve this, kinetic energy must be greater than the intermolecular forces that keep molecules bonded. The amount of energy needed to vaporize a quantity of liquid at a given pressure and a constant temperature is called the heat of vaporization. When liquid water is vaporized, it turns into steam.

Adding heat to a liquid until it reaches its boiling point is one method of vaporization. Boiling is a type of vaporization that occurs when vapor bubbles form beneath the surface of the liquid. The boiling point varies based on atmospheric pressure. With more atmospheric pressure, more energy is needed to reach the boiling point. At sea level, water boils at 100 oC (212 oF)—this sea level temperature is called the normal or atmospheric boiling point. At higher elevations, water requires less energy to boil. On Mount Everest, water boils at about 71 oC (160 oF). In space, which lacks an atmosphere but is also extremely cold, water will first boil and then freeze—a consequence of the high heat capacity of water. Evaporation, another type of vaporization, occurs below the boiling point. In this process, water molecules with enough kinetic energy to surpass intermolecular forces escape the surface of the water as vapor. The remain

 Core: Chemistry of Life

States of Water

JoVE 10668

Water exists in three main states: solid (ice), liquid, and gas (steam). The state water is in depends on the intermolecular forces that draw water molecules together and the kinetic energy that pulls them apart.

Water freezes when the intermolecular forces are greater than the kinetic energy. Unlike most other substances, water is less dense in its solid state than it is in its liquid state. This is because each water molecule is capable of bonding with four molecules, forming a spaced, tetrahedral organization. This characteristic of water allows ice to float. Without floating ice, bodies of water would freeze from the bottom up, killing aquatic life. When kinetic energy is applied to ice in the form of heat, ice melts into liquid water. In this state, bonds between water molecules constantly break and form again. When ice melts, the temperature of the water remains at the melting point until the whole volume is liquid. Only then will the water temperature increase beyond the melting point. As kinetic energy overpowers intermolecular forces, liquid water (or even ice) turns into a gas. The process of generating steam from liquid water is called vaporization. Increases in kinetic energy can occur within the sample, as with boiling, or can happen at the surface when water evaporates. The process by which a gas is generated directly from a solid, witho

 Core: Chemistry of Life

Purification of Ferrocene by Sublimation

JoVE 10429

Source: Tamara M. Powers, Department of Chemistry, Texas A&M University 

Sublimation, the direct phase transition of a solid into a gas without first becoming a liquid, takes place at temperatures and pressures lower than that of the compound's triple point (Figure 1).The process of sublimation can be utilized …

 Inorganic Chemistry

Conservation of Energy Approach to System Analysis

JoVE 10449

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI

The purpose of this experiment is to demonstrate the application of the energy conservation equation to determine the performance of a flow system. To this end, the energy equation for steady,…

 Mechanical Engineering

Schlenk Lines Transfer of Solvents

JoVE 5679

Source: Hsin-Chun Chiu and Tyler J. Morin, laboratory of Dr. Ian Tonks—University of Minnesota Twin Cities

Schlenk lines and high vacuum lines are both used to exclude moisture and oxygen from reactions by running reactions under a slight overpressure of inert gas (usually N2 or Ar) or under vacuum. Vacuum transfer has been developed …

 Organic Chemistry

Operating the Glovebox

JoVE 10378

Robert M Rioux, Ajay Sathe, Zhifeng Chen, Pennsylvania State University, University Park, PA

A glovebox is an isolated enclosure that is designed to maintain an inert atmosphere. The manipulation of chemicals or apparatus is done via the use of gloves, which allow operation while still maintaining an inert atmosphere. A positive pressure…

 Lab Safety

Mass Conservation and Flow Rate Measurements

JoVE 10445

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI

The purpose of this experiment is to demonstrate the calibration of a flow passage as a flowmeter using a control volume (CV) formulation [1, 2]. The CV analysis focuses on the macroscopic effect of flow …

 Mechanical Engineering

Determination of Impingement Forces on a Flat Plate with the Control Volume Method

JoVE 10444

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI

The purpose of this experiment is to demonstrate forces on bodies as the result of changes in the linear momentum of the flow around them using a control volume formulation [1, 2]. The control volume…

 Mechanical Engineering

The Effect of Reflux Ratio on Tray Distillation Efficiency

JoVE 10432

Source: Kerry M. Dooley and Michael G. Benton, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA

Tray and packed columns are both commonly used for distillation, absorption, and stripping separation operations.1,2 The goal of this experiment is to distill a mixture of alcohols (methanol, isopropanol) and water …

 Chemical Engineering

Preparing Anhydrous Reagents and Equipment

JoVE 10227

Source: Laboratory of Dr. Dana Lashley - College of William and Mary
Demonstrated by: Timothy Beck and Lucas Arney

Many reactions in organic chemistry are moisture-sensitive and must be carried out under careful exclusion of water. In these cases the reagents have a high affinity to react with water from the atmosphere and if left…

 Organic Chemistry

Rotary Evaporation to Remove Solvent

JoVE 5501

Source: Dr. Melanie Pribisko Yen and Grace Tang — California Institute of Technology

Rotary evaporation is a technique most commonly used in organic chemistry to remove a solvent from a higher-boiling point compound of interest. The rotary evaporator, or "rotovap", was invented in 1950 by the chemist Lyman C. Craig. The…

 Organic Chemistry

Regulating Temperature in the Lab: Preserving Samples Using Cold

JoVE 5042

Preservation of laboratory samples, specimens, and reagents using extreme cold is routinely performed in biomedical research labs. This video will discuss some of the methods for keeping laboratory samples cold and will explain the correct cooling method to use for each experimental requirement.

For example, cooling agents, such as ice…

 General Laboratory Techniques

Vapor-liquid Equilibrium

JoVE 10425

Source: Michael G. Benton and Kerry M. Dooley, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA

Vapor-liquid equilibrium is paramount in engineering applications such as distillation, environmental modeling, and general process design. Understanding the interactions of components in a mixture is very…

 Chemical Engineering

Proper Operation of Vacuum Based Equipment

JoVE 10377

Source: Robert M. Rioux, Ajay Sathe & Zhifeng Chen, Pennsylvania State University, University Park, PA

Vacuum is required for a number of laboratory procedures. This is most routinely achieved in the laboratory by the use of vacuum pumps. In addition to working at low pressures, vacuum pumps can also be used to enable…

 Lab Safety

X-ray Photoelectron Spectroscopy

JoVE 10474

Source: Faisal Alamgir, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA

X-ray photoelectron spectroscopy (XPS) is a technique that measures the elemental composition, empirical formula, chemical state and electronic state of the elements that exist within a material. XPS spectra are obtained by…

 Materials Engineering

Glovebox and Impurity Sensors

JoVE 10317

Source: Tamara M. Powers, Department of Chemistry, Texas A&M University 

The glovebox provides a straightforward means to handle air- and moisture-sensitive solids and liquids. The glovebox is what it sounds like: a box with gloves attached to one or more sides, which allows the user to perform manipulations within the glovebox under an inert…

 Inorganic Chemistry

Hot Wire Anemometry

JoVE 10464

Source: Ricardo Mejia-Alvarez and Hussam Hikmat Jabbar, Department of Mechanical Engineering, Michigan State University, East Lansing, MI

Hot-wire anemometers have a very short time-response, which makes them ideal to measure rapidly fluctuating phenomena such as turbulent flows. The purpose of this experiment is to demonstrate the use of…

 Mechanical Engineering

Kinetics of Addition Polymerization to Polydimethylsiloxane

JoVE 10369

Source: Kerry M. Dooley and Michael G. Benton, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA

Polymers are molecules consisting of many repeating monomer units that are chemically bonded into long chains. They exhibit a broad range of physical properties, which are affected by their chemical structure,…

 Chemical Engineering

Fractional Distillation

JoVE 5700

Source: Laboratory of Dr. Nicholas Leadbeater — University of Connecticut 

Distillation is perhaps the most common laboratory technique employed by chemists for the purification of organic liquids. Compounds in a mixture with different boiling points separate into individual components when the mixture is carefully distilled.…

 Organic Chemistry


JoVE 10344

Source: Ketron Mitchell-Wynne, PhD, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA

When a pot of water is placed on a hot stove, heat is said to "flow" from the stove to the water. When two or more objects are placed into thermal contact with each…

 Physics I

Dissolved Oxygen in Surface Water

JoVE 10016

Source: Laboratories of Margaret Workman and Kimberly Frye - Depaul University

Dissolved oxygen (DO) measurements calculate the amount of gaseous oxygen dissolved in surface water, which is important to all oxygen-breathing life in river ecosystems, including fish species preferred for human consumption (e.g. bluegill and bass),…

 Environmental Science

In Situ Monitoring of the Accelerated Performance Degradation of Solar Cells and Modules: A Case Study for Cu(In,Ga)Se2 Solar Cells

1TNO Solliance, Thin Film Technology, 2Eternal Sun, 3Hielkema Testequipment, 4Institut des Matériaux Jean Rouxel (IMN)-UMR 6502, Université de Nantes, CNRS, 5ReRa Solutions BV, 6Institute of Molecules and Materials, Radboud University

JoVE 55897


Combining Single-molecule Manipulation and Imaging for the Study of Protein-DNA Interactions

1LENS - European Laboratory for Non-linear Spectroscopy, University of Florence, 2Chemistry Research Laboratory, University of Oxford, 3Department of Biology, University of Florence, 4Department of Physics and Astronomy, University of Florence, 5National Institute of Optics-National Research Council, Italy, 6International Center of Computational Neurophotonics

JoVE 51446


Rapid and Low-cost Prototyping of Medical Devices Using 3D Printed Molds for Liquid Injection Molding

1Department of Bioengineering & Therapeutic Sciences, University of California, San Francisco, 2Department of Obstetrics, Gynecology & Reproductive Sciences, University of California, San Francisco, 3Keck School of Medicine, University of Southern California

JoVE 51745


Spontaneous Formation and Rearrangement of Artificial Lipid Nanotube Networks as a Bottom-Up Model for Endoplasmic Reticulum

1Centre for Molecular Medicine Norway, Faculty of Medicine, University of Oslo, 2Department of Chemistry, Faculty of Mathematics and Natural Sciences, University of Oslo, 3Department of Chemistry and Chemical Engineering, Chalmers University of Technology

JoVE 58923

More Results...