Atmospheric Pressure

Did you know that air has weight? This illustrated essay from the NOVA Web site explores conditions that affect air density and atmospheric pressure.

Bend, Twist and Break: Beyond the Laboratory

Dr. Chris Muhlstein explains that when scientists study fracture surfaces from controlled experiments to understand the resulting shapes and features, they can use their understanding to deduce what happened when they were not around to see the material fail or break. Further they can predict what will have to a larger or smaller piece of material under stress. This process is how scientists and engineers translate a lab experiment into a design for an airplane, bridge or even a bike frame.

Accessibility features: Caption

Bend, Twist and Break: Breaking Glass

Dr. Chris Muhlstein explains that researchers learn about the scientific basis for failure of materials by running experiments in the lab, using a simple shape like a glass rod to calculate the strength of material and predict its failure. The same tests can be done at the micro and nano scale using tiny specimens. Students can run a similar experiment with a bar of chocolate.

Accessibility features: Caption

Bend, Twist and Break: Fracture Surfaces

Dr. Chris Muhlstein explains that fracture surfaces can reveal how and why a material has failed. An image of a fracture surface has features or shapes that we can use to understand where a material failed and why. Scientists use an optical microscope or a scanning electron microscope to read a fracture surface at high magnifications, much like we read maps to find our way.

Accessibility features: Caption

Bend, Twist and Break: The Bridge

Dr. Chris Muhlstein explains that the arrangement of atoms in a material determines the properties. He drops an iPod to illustrate how the arrangement of atoms can protect it from damage; he narrates footage of the collapse of the Tacoma Narrows Bridge in the 1940s to show how the deformation of materials can cause the collapse of a structure.

Accessibility features: Caption

Breaking Things on Purpose

*Materials such as metals (aluminum, iron, copper, etc.), ceramics (silicon carbide, porcelain) or polymers (milk jugs made of polyethylene) are tested by scientists and engineers to reveal certain mechanical properties such as the maximum stress a material can withstand. The stress at which a material breaks is a measure of its strength. In this lesson you will be testing the strength of a delicious material you know as chocolate!

Buoyancy Basics

This illustrated demonstration from the NOVA Web site explains the concepts of buoyancy and density by showing what happens when different kinds of wood blocks are dropped in water.

Buoyancy Brainteasers: Balloon-in-Car Puzzler

This interactive brainteaser from the NOVA Web site challenges you to explain the behavior of a helium-filled balloon in a moving car.

Buoyancy Brainteasers: Boat-in-Pool Puzzler

This interactive brainteaser from the NOVA Web site challenges you to figure out what happens to the water level when a rock is resting in a boat and when it is submerged in water.

Buoyancy Brainteasers: Buoyancy Question

This interactive brainteaser from the NOVA Web site challenges you to figure out what causes an object to sink.

Cooking with Sugar

Find out about the chemistry of candy and how sugar reacts at different temperatures to become fudge, caramel, lollipops, and more in this interactive activity adapted from the Exploratorium.

Density and Buoyancy: Experimenting with Club Soda

In this video segment adapted from ZOOM, the cast discovers that gas-filled bubbles act like life jackets for raisins, making them buoyant.

Accessibility features: Caption, Transcript

Density and Buoyancy: Making Eggs Float

Why does an egg float in salt water? Learn about density and buoyancy in this video segment adapted from ZOOM.

Accessibility features: Caption

Density and Buoyancy: Mixing Hot and Cold Water

Watch warm water float on top of cold water in this video segment adapted from ZOOM.

Accessibility features: Caption, Transcript

Density and Buoyancy: Pouring Air into Water

This video segment adapted from ZOOM offers a clever demonstration of buoyancy by showing how to pour a cup of air into a cup filled with water.

Accessibility features: Caption, Transcript

Density and Buoyancy: Testing Liquids

Will a grape float in oil? Will a metal nut sink in corn syrup? Watch as the ZOOM cast tests the buoyancy of a variety of liquids and objects.

Accessibility features: Caption, Transcript

Diamonds: The Science Behind the Sparkle

This illustrated essay from the NOVA Web site explains why the atomic structure of a diamond slows down light and produces a sparkle more brilliant than from any other colorless substance.

Disappearing Milk

A magician pours milk into a glass, but when he turns the glass upside down, nothing comes out. How does he do it? Discover the science behind the "magic" in this video adapted from the American Society of Mechanical Engineers.

Discovering Air

Our understanding about the air we breathe has changed dramatically through time. This illustrated timeline from the NOVA Web site tracks the changing thought on air and the creation of the Periodic Table of the Elements.

Dissolving Salts in Water

In this interactive activity adapted from Iowa State University, design and carry out an experiment: dissolve salts in water, see how different ionic compounds produce different reactions, and observe the resulting changes in temperature.