• Physics is Phun October 2022
  • Demonstration Highlight of the Week: Air Tables
  • Past Highlight: Reflecting Telescope Models
  • Past Highlight: Gravitational Lensing Model
  • Demonstrations
  • How many demonstrations?
  • New Resource: Directory of Simulations
  • Spotlight: COVID-19 Animation and UMD Research
  • New Resource: Demonstration Video Channel
  • Visit the UMD COVID-19 Dashboard
  • Welcome to Autumn 2022! 

Physics is Pun presents

The Physics of Sound

 A presentation of demonstrations of the physical science underlying the world of sound and music. 

at the University of Maryland's John S. Toll Physics Building

Friday, October 14th, at 7:00 PM.

Registration and directions at

 flyer for The Physics of Sound Friday October 14th &PM

 We have many demonstrations of the mechanics of collisions in our collection. You can explore them in section C7 of our website.

 a collage of many demonstrations of collisions

 Among the most valuable for illustrating all kinds of collisions are the air table demonstrations, the large C7-42 and the smaller C7-43, and their portable cousin the hoverpucks, C7-44. All three of these demonstrations use pucks floating on a cushion of air to allow you to show very low friction collisions with various masses. The air tables use an air blower beneath the surface, while the hoverpucks have their own integral fans so they can skitter across the floor of the classroom. All three, of course, require quite a bit of space to use!

Demonstration C7-42: large air table with pucks

 So it’s a valuable supplement to them that the PhET Collection at the University of Colorado Boulder has introduced their online simulated Collision Lab, which lets you experiment with collisions of pucks at the comfort of your desk or couch. You can use the air table in the classroom, then try to replicate the experiment at home for further analysis!




The most popular design of telescopes for astronomical research is the reflecting telescope. First developed in the 17th century, the typical reflecting telescope uses a curved primary mirror to focus incoming light, and a secondary mirror to direct that light to an eyepiece or sensor. There are many variations on the design, but the underlying principle is the same: light is focused largely by reflection, rather than refraction as in a lens-based Galilean refracting telescope, which allows them to avoid both the chromatic aberration common to lenses and the weight required to create very large ones. Reflecting telescopes have a long history in astronomy and astrophysics, from William and Caroline Herschel to the Hubble Space Telescope and beyond.

 reflecting telescope mosaic: A, diagram of a typical reflecting telescope, after Pearson Scott Foresman; B, diagram of a Schmidt-Cassegrain reflecting telescope, after Griffinjbs; C, photograph of an 18th century astronomical reflecting telescope built by astronomer William Herschel; D, photograph of the Hubble Space Telescope

We have two models in our collection of how reflecting telescopes work. Demonstration L7-14 models the behaviour of light in a reflecting telescope on our optical board, which uses real optical elements to create a viewable two-dimensional ray diagram.

Demonstration L7-14: Light is focused by a large concave mirror and then directed towards an observer by a smaller mirror

We also have a static model, demonstration E2-54, which shows the construction of a typical reflecting telescope with strings to represent the paths of light rays through the device. The two are best used in combination to show students how this system lets us observe distant objects.

 Demonstration E2-54: a plastic and string model of a reflecting telescope

You can experiment with this at home as well, with this simulation from JavaLab. You can adjust the angle of the incoming light and see how it reflects off the primary mirror and forms an image at the secondary mirror, and use an eyepiece lens to focus it on an observer. Try it out at


In astronomy, gravitational lensing is the phenomenon whereby gravitational forces around a mass bend light in a way similar to a conventional refracting lens does. When a large mass lies between an observer and the light source they're observing, sometimes that mass can bend the incoming light, causing the source to appear in a different location, or even in multiple locations at once. This can even allow an observer to see a light source that would otherwise be unobservable due to being directly behind another object.

E1 21: the lens

We have a model of this in our collection, as demonstration E1-21, a glass lens that is specially shaped to produce a similar effect to gravitational lensing. Light is bent more the closer it is to the lens' center axis. As a light source moves behind the lens, you can see the source appear to be displaced, or even see one source appear to become several, or become a ring of light around the center of the lens. All of these phenomena can be seen from gravitational lensing in space as well.

E1 21: cutaway drawing

In this drawing, you can see a cross section of part of the lens. The changing curvature produces the gravity-like effect of increasing refraction towards the center.

Try experimenting with this simulation to see it in action in a starfield!

Read more:

 gravitational lensing diagram - path of light around a mass, by R. O. Gilbert

We’re often asked how many demonstrations we have in the collection. That’s a more complex question than it might at first seem.

At last count, we have just over 1,500 demonstrations published to the website – that is, that’s how many demonstration pages exist in the collection. But some pages describe a single setup than can be used in several different ways. Take a look at K2-61: Thomson’s Coil, for example. This single page actually describes four different, related demonstrations that can be performed with this device. They don’t require very different equipment to be delivered, just slight changes in preparation, though, and they’re usually all relevant at approximately the same point in a syllabus, so it’s simpler to list them all in one place. Conversely, there are many demonstrations that use the Optical Board – browse through section L and you will see many of them! Since ray optics is divided into several sections in the demonstrations catalog, each of the configurations of the Optical Board is listed separately, to make it easier to find the one you need; and if you’re only doing one demonstration with it, we can configure it for you in advance to save you time in class.

On the other hand, consider M1-12 and H2-22. These are both listings for Interference Transparencies, a popular way to illustrate the interaction of wavefronts. Here, we made the unusual decision to list the same demonstration twice in two different sections, since otherwise someone planning a course on sound might not think to look for relevant demonstrations in the optics section, and vice-versa. These occasional cross-references make it easier to find the demonstrations you need for your class.

And even aside from the demonstration listings as they stand, we’re often called on to combine equipment in unique ways to demonstrate something new! If it’s a combination that’s likely to be repeated or that proves useful to others, it will be added to the website, but we’re generally open to creatively reinterpreting demonstrations to fit a new class context.

Every year we add more demonstrations to the collection; and occasionally a demonstration is retired, if it no longer meets an instructional need or has been superseded by others. So defining just how many demonstrations we have might not be the right question to ask. Ask, rather, what can we demonstrate for you today?

In support of most classes moving to an online model this year, the Lecture-Demonstration staff are doing our part to help connect you to resources you need for teaching remotely. As one part of this project, we have begun compiling a Directory of Simulations from around the internet, organized by general area of physics. Find it under the Tools and Resources menu above, or click the image below.

Sample subsection titles: Electricity & Magnetism Simulations, Mathematics Simulations, Optics Simulations, Oscillations & Waves Simulations, Quantum Simulations, Thermodynamics & Statistical Mechanics Simulations

There are a tremendous number of simulations out there, that folks have been creating for years. We’re testing them out, choosing ones that we can confirm currently work (always a question as internet technology marches on) and that seem useful for our department’s classes. As of this posting, we have just over fifty simulations collected. Our initial focus has been on physics that is hard to demonstrate in the classroom, or experiments that are difficult to present as static pictures or live video.

This project is ongoing! As we continue to explore we will be adding more subjects and more demonstrations per subject. We also invite recommendations! If you have a favourite simulation, let us know (email lecdemhelp at so we can check it out and add it to the directory.

We’ll have more new projects posted soon; watch the site for news!


In our ongoing work to support remote teaching, we are pleased to announce a new resource. Over the summer of 2020, a Teaching Innovation Grant helped to create our new Demonstration Videos. These can be used for remote, hybrid, and in-person classes to present demonstrations in conjunction with class engagement questions.

The videos have their own YouTube channel, linked both here and on the Tools & Resources Menu above; check them out today!


Science is all about data, and our current pandemic is no different. 

Be sure to check the UMD COVID-19 Dashboard for the latest campus data and links to reopening plans and  proper safety procedures.

Keep Terps Safe - UMD COVID Public Dashboard



We at the Physics Lecture-Demonstration Facility look forward to working with you for your demonstration needs this semester, to help make your physics classes engaging and informative.

Be sure to explore our new online resources as well, including the demonstration videos channel, LecDem blog, and the directory of simulations. Keep an eye out for new material to come!

If you have any questions about finding the right demonstrations or other resources for your class, access to the order form, or anything else we can help with, be sure to call or email.

Please remember to order your demonstrations before the cutoff deadline for the order form system: For morning classes, before 1PM the previous working day; for afternoon classes, before 4AM the day of the class. Where possible, we appreciate having the orders at least one full working day ahead, to ensure plenty of time to make sure everything is ready for you.

LecDemBlog (maintopa)

The Physics Question of the Week is a tradition at the University of Maryland, first created by Dr. Richard E. Berg in 2000. Each week, we have highlighted one of our many demonstrations by asking a physics question relevant to the topic designed to be illustrated. This not only challenges audiences to carefully examine their previously held views on physics, but also provides suggestions for teachers looking to use these demonstrations in their own classrooms.

Be sure to visit our discussion forum for discussion of many physics demonstrations, including links to Questions of the Week about them.