In high school, and also in introductory physics courses in higher levels of schooling, the law of universal gravitation of planets is introduced by postulating Johannes Kepler's three laws, and later Isaac Newton's law of the inverse of the square of the distance to the Sun. The justification of the laws is only achieved in advanced courses in…

We study the variation of the apparent weight of an object with height above the surface of a planet with a (buoyant) atmosphere. Interestingly, this variation depends on two competing factors--the reduced gravitational acceleration (which acts to reduce the weight with increasing height) and the reduced buoyancy force in the progressively less…

Even though many physics teachers take their students on a calculation adventure through circular motion and Newton's universal law of gravity to determine Earth's velocity, most of us leave it at that. We present the final result and say, "Look, Earth is moving around the Sun at about 107,000 km/hr (66,000 mph), yet we can't feel the motion…

Stellar aberration is the phenomenon whereby the observed angular position of a star depends on the relative motion between the star and Earth. Specifically, a telescope must be tilted slightly into the direction of motion of Earth relative to the star. There are in fact three different angular positions of interest: the observed position of the…

The tidal forces generated by a black hole can be so powerful that they cause unlimited stretching, known as spaghettification. A detailed analysis of this phenomenon requires the use of Einstein's theory of general relativity. The aim of this paper is to offer an up-to-date and accessible analysis of spaghettification, in which the complex…

This paper has a didactic aim. Indeed, starting from the well-known principle of free fall discovered by Galileo Galilei, we want to make some reflections that we consider useful for secondary school students. Being the acceleration invariant with respect to Galilei's transformations, it is useful to underline that the free fall in a gravitational…

We propose an experimental analogy to verify Kepler's second law using a spherical pendulum. We made a movie of a closed elliptical orbit of the pendulum and extracted the data position using the Tracker software. Analyzing the data, we measured the areas that the position vector sweeps showing the validity of Kepler's second law.

How far, in space, can we see? And can we see an object whose Hubble recessional velocity exceeds the speed of light? Maybe you've thought about these questions before, or perhaps you've seen them discussed in the literature or mentioned in the media. With the recent popularity of inflation and Big Bang cosmology, they're hard to avoid. The…

Video analysis with a 30 Hz frame rate is the standard tool in physics education. The development of affordable high-speed-cameras has extended the capabilities of the tool for much smaller time scales to the 1 ms range, using frame rates of typically up to 1000 frames s[superscript -1], allowing us to study transient physics phenomena happening…

In a spiral galaxy, the stars move in a circular motion around the galactic center, and the relation between velocity and the orbital radius is referred to as the rotation curve. Previous astronomical observation data indicate that the rotation curve is flat at the periphery of the galaxy, which completely dissatisfies Keplerian decline. Assuming…

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…

Planetary motion in physics learning is an abstract concept and requires high reasoning. This article is one of the augmented realities (AR)-based pocketbook development on the planetary motion, focusing on student learning achievement. The study used the ADDIE model : "Analysis-Design-Development-Implementation-Evaluation". In the…

There are five unique points in a star/planet system where a satellite can be placed whose orbital period is equal to that of the planet. Simple methods for calculating the positions of these points, or at least justifying their existence, are developed.

The observation that the shadows of objects change during the course of the day and also for a fixed time during a year led curious minds to realize that the Sun could be used as a timekeeper. However, the daily motion of the Sun has some subtleties, for example, with regards to the precise time at which it crosses the meridian near noon. When the…

Experimental teaching is essential for a good understanding of science, especially on Physics. Practical activities play an important role for engaging students with science, mainly when they interact directly with equipment, collect experimental data with computers and/or use interactive software for data analysis. In this work, we present the…