Khan Academy
Khan Academy: Isotopes and Mass Spectrometry
Tutorial explains isotopes, atomic weight and how isotopes can be detected using mass spectrometry. Examples are given.
PBS
Pbs Learning Media: Floating and Sinking: Hot Air Balloons
Why do hot air balloons float? This resource from the NOVA Web site offers a series of interactive activities that illustrates the physics of hot air balloons.
Other
Conversions for Weight Measurements
This site allows you to convert weight/mass measurements. For example converting tons to grams. CCSS.Math.Content.3.MD.A.2 Measure and estimate liquid volumes and masses of objects using standard units
PBS
Pbs Learning Media: Matter's Physical Properties: Interactive Lesson
In this interactive lesson, learn what the "physical properties" of matter are and how can they be measured and observed.
ibiblio
Ibiblio: How Many? A Dictionary of Units of Measurement
The Center for Mathematics and Science Education at the University of North Carolina at Chapel Hill provides an interesting and easy-to-use dictionary of the history and meaning of many measurement terms. Metric, International, and...