Dedicated to the strengthening of the teaching of introductory physics at all levels, The Physics Teacher provides peer-reviewed materials to be used in the classrooms and instructional laboratories. It includes:
Innovative physics demonstrations; New ways of doing lab experiments; Ideas for presenting difficult concepts more clearly; Suggestions for implementing newer technology into teaching; Historical insights that can enrich the physics course and Book and film reviews.
Special features include Physics Challenge Solutions, Fermi Questions, and Figuring Physics.
Tyrannosaurus Rex: A pathetic vestigial organ or an integral part of a fearsome predator?" title="Forelimbs of Tyrannosaurus Rex: A pathetic vestigial organ or an integral part of a fearsome predator?" />
In this paper, we examine a first-year torque and angular acceleration problem to address a possible use of the forelimbs of Tyrannosaurus rex. A 1/40th-scale model (see Fig. 1) is brought to the classroom to introduce the students to the quandary: given that the forelimbs of T. rex were too short to reach its mouth, what function did the forelimbs serve? This issue crosses several scientific disciplines including paleontology, ecology, and physics, making it a great starting point for thinking “outside the box.” Noted paleontologist Kenneth Carpenter has suggested that the forelimbs of T. rex were an integral part of its predatory behavior. Given the large teeth of T. rex, it is assumed that they killed with their teeth. Lipkin and Carpenter1 have suggested that the forelimbs were used to hold a struggling victim (which had not been dispatched with the first bite) while the final, lethal bite was applied. If that is the case, then the forelimbs must be capable of large angular accelerations α in order to grab the animal attempting to escape. The concepts of the typical first-year physics course are sufficient to test this hypothesis by solving . Naturally, students love solving any problem related to Tyrannosaurus rex!
Educators have found that kinesthetic involvement in an experiment or demonstration can engage students in a powerful way.1–3 With that as our goal, we developed three activities that allow students to connect with and quantitatively explore key physics principles from mechanics with three fun physical challenges. By presenting these activities as competitions, we can challenge students to use what they know about the relevant physics to improve their performance and beat their own score or those of other students. Each activity uses an original, real-time data collecting program that offers students and educators a simple, clear method to demonstrate various physics concepts including: (1) impulse momentum, (2) center of mass (COM), and (3) kinematics. The user interface, written in LabVIEW, is intuitive to operate and only requires Vernier Force Plates,4 a Vernier LabQuest,5 a webcam, and a computer. In this article, we will describe each of these activities, all of which are well suited and readily available for other outreach events or classroom demonstrations.
The traditional introductory-level meterstick-balancing lab assumes that students already know what torque is and that they readily identify it as a physical quantity of interest. We propose a modified version of this activity in which students qualitatively and quantitatively measure the amount of force required to keep the meterstick level. The setup for this experiment also introduces upward forces in addition to downward forces. In this very accurate experiment, the torque equation can be discerned directly from the data, and torque's symmetry between upward and downward forces naturally arises.
During a recent ride in an elevator, I was startled by an observation. Once the door closed, the features on the back wall of the elevator were evident in a reflection on the door; however, my own reflection appeared absent (see Fig. 1). How could that be? What physics caused this curious phenomenon? The elevator had wooden molding, including horizontal strips that ran all the way around the back and sides (see Fig. 2). These horizontal strips were what showed up most clearly in the reflection. The door's surface was brushed metal with the brush marks all running vertically. Therein lay the solution.
Almost everyone “knows” that steam is visible. After all, one can see the cloud of white issuing from the spout of a boiling tea kettle. In reality, steam is the gaseous phase of water and is invisible. What you see is light scattered from the tiny droplets of water that are the result of the condensation of the steam as its temperature falls below 100 °C (under standard conditions).