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Video motion analysis allows tracing trajectories of objects in motion and is an established method in physics education. Tablet computers, with their integrated cameras, offer the opportunity to both record and analyze dynamic motions during experiments on a single device. This enables students to work without transitioning the data between camera and computer, but with ubiquitously available applications on mobile devices. This article describes a model experiment to examine Kepler’s laws of motion using tablet computers with a video analysis application.

The family of paths of ideal projectiles shot from a point with a common value of speed and at different angles to the horizontal has several interesting properties associated with it. For example, Chapou et al. have shown that an ellipse passes through the apexes of these parabolic paths. This observation encouraged us to further explore this family of the parabolic paths. In this note we show the presence of a hidden circle in the family of these paths. We highlight all the known interesting properties of this family of projectiles. For our purpose here, we consider projectiles shot from points on the third quadrant of a circle in the vertical plane. In this method, we don’t use vectors or calculus or Newton’s laws of motion.

The acceleration of a vehicle or a bicycle is commonly used in elementary physics courses to illustrate problems concerning Newton’s laws of motion when friction forces are involved. The maximum possible acceleration is rarely discussed, although it is of interest to consumers and racing car enthusiasts, and it is sometimes questioned by students. It is the main focus of the present article and is considered from a basic physics point of view, appropriate for classroom discussion.

Anyone who has taught introductory physics should know that roughly a third of the students initially believe that any object at rest will remain at rest, whereas any moving body not propelled by applied forces will promptly come to rest. Likewise, about half of those uninitiated students believe that any object moving at a constant speed must be continually pushed if it is to maintain its motion. 1 That's essentially Aristotle's law of motion and it is so “obviously” borne out by experience that it was accepted by scholars for 2000 years, right through the Copernican Revolution. But, of course, it's fundamentally wrong. This paper tells the story of how the correct understanding, the law of inertia, evolved and how Newton came to make it his first law.

Newton's laws are difficult both for teachers and students at all levels.1–3 This is still the case despite a long history of critique of the laws as presented in the classroom. For example, more than 50 years ago Eisenbud4 and Weinstock5 proposed reformulations of the laws that put them on a sounder, more logically consistent base than is presented in many textbooks without resorting to “intuitional or anthropomorphic contrivances.”5 In 1990, Arnold Arons6 wrote that “the Law of Inertia and the concept of force have, historically, been two of the most formidable stumbling blocks for students.” One might imagine, therefore, that by 2012 remedial strategies would have resolved these difficulties, but there is little evidence that the problem has been satisfactorily addressed. Diagnostic tools such as the Force Concept Inventory7,8 have cast light on areas of difficulty; remedial strategies have included historical approaches, computer simulations, analogical approaches, and many more.9–12 Nevertheless, pap...

Baking soda and vinegar water bottle rockets provide a fun, cheap way of illustrating Newton’s laws of motion. This article describes safe, reliable improvement over the traditional design of this rocket that will achieve a height of 50 ft.

In this paper we use scalar energy, rather than vector force and momentum, to predict how a particle will move. The result is a quantity called action. Action and its relatives undergird Newton's laws and transcend them, also predicting motion in the quantum world and in the curved spacetime of general relativity. An example exhibits action in action.

In traditional introductory physics courses, the topic of projectile motion is discussed before the introduction of Newton’s laws of motion and a discussion of forces. I discuss some possible pedagogical advantages to reversing the order of presentation.

Although the principle of momentum conservation is a consequence of Newton's second and third laws of motion, as recognized by Newton himself,1 this principle is typically applied in analyzing collisions as if it is a separate concept of its own. This year I sought to integrate my treatment of collisions with my coverage of Newton's laws by asking students to calculate the effect on the motion of two particles due to the forces they exerted for a specified time interval on each other. For example, “A 50-kg crate slides across the ice at 3 m/s and collides with a 25-kg crate at rest. During the collision process the 50-kg crate exerts a 500 N time-averaged force on the 25 kg for 0.1 s. What are the accelerations of the crates during the collision, and what are their velocities after the collision? What are the momenta of the crates before and after collision?”

We present and discuss a physics demonstration, similar to, but distinct from, the ballistic-pendulum demonstration, one that illustrates all three conservation laws of mechanics (for energy, momentum, and angular momentum) simultaneously.

Would you like to build an inexpensive, highly visible, quickly assembled device that dramatically illustrates Newton's three laws of motion? This model incorporates sturdiness, high-profile visibility, and a student interest component that is sure to capture and hold their attention.

Nonsense! No mass can change its state of motion unless a force acts on it. But acceleration without any force is just what introductory textbook authors are implying when their only explanation of changes in rotational motion is the conservation of angular momentum with no mention of any force. Conservation laws connect the initial and final states of a system, correctly predicting the final state, but they do not reveal how the change is made or what forces are acting to produce that change. This paper discusses two applications found in introductory texts and includes some dynamics that clarify the motions.

Presented here is an adaptation of George Gamow's derivation of the centripetal acceleration formula as it applies to Earth's orbiting Moon. The derivation appears in Gamows short but engaging book Gravity,1 first published in 1962, and is essentially a distillation of Newton's work. While TPT contributors have offered several insightful derivations of the formula,2,3 students might find this “real world” version more accessible. In addition, this particular derivation requires a durable understanding of both the Galilean equations and Newtonian laws of motion, and therefore serves as review of these key concepts.

We present an analysis of a situation described in Milton’s epic poem “Paradise Lost” in which we calculate the distance required for a nine-day free-fall from rest to the Earth. The resulting method is completely general, and can be applied to free-fall toward other bodies and to near-Earth free-fall as well.

Atwood’s machine is a standard experimental apparatus that is likely to get pushed out of the laboratory portion of the general physics course due to the ever increasing use of microcomputers. To avoid this, I now use the apparatus for an experiment during the work and energy portion of the course which not only allows us to demonstrate those principles but also compare them with Newton’s laws of motion.

A simple game is presented to illustrate the application of Newton’s laws of motion. This game has been used for several years in teaching introductory physics at Shippensburg University.

Newton’s second law is commonly misapplied to systems of multiple particles, as was done in a recent note in The Physics Teacher. This note revisits the problem of a rope sliding in an L-shape tube.