Welcome back! Today we’re taking a look at a popular demonstration related to the concept of relativity.
When we observe and measure motion, we are inevitably making the measurement against some frame of reference. An inertial reference frame is the technical term for a frame of reference in which an object is observed to have no outside forces acting on it, so that it is moving freely in space. Sometimes we have to go to great lengths to determine what such a frame of reference might be – and in the case of Demonstration P1-02, it is literally a metal frame!
Read more about this exciting demonstration and how it can be used in class in our latest blog post.
In recent years, the classic term “moment of inertia” has started to be largely retired in favor of the more descriptive “rotational inertia;” likely a good choice, as “moment” has long since ceased to have any non-time-related usage in everyday English. But call it what you will, it can be a challenging concept for beginning students to wrap their heads around.
Demonstration D2-01: Ring and Disc on Inclined Plane is a useful illustration for clarifying this concept. Two objects of similar mass and radius, a metal ring and a solid wooden disc, are placed on an inclined plane with no initial velocity. As they are accelerated by gravity, the disc quickly outpaces the ring. You can invite students to make a prediction ahead of time about their behaviour, presenting it as a race between the two objects, and invite them to discuss the results afterwards.
Read more on our blog!
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.
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 physics.umd.edu) 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!
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.
Welcome to Fall 2025! We at the Lecture Demonstration Facility are looking forward to working with you in the spring semester.
We appreciate as much advance notice of demonstrations as you can give; but at a minimum, please remember to order your demonstrations before the order cutoff deadline.
- For morning classes, orders must be in before 1PM the previous working day.
- For afternoon classes, order must be in before 4AM the day of the class.
We appreciate receiving demo orders a minimum of one full working day ahead, to ensure plenty of time for preparation. As always, we’ll meet with you before your class to answer questions, explain safety measures, and review demonstration procedures.
Here’s to another great semester at UMD Physics!
