The Strangest Force

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Resonance—Surprises in the Intricate Dance
Resonance happens whenever a small periodic force produces a large effect on a periodic motion--for example, when you push a child on a swing. Learn how resonance due to gravitational interactions between three bodies can lead to amazing phenomena with planets, asteroids, and rings of planets.
Free Fall and Inertia
Review three great discoveries by the "grandfather" of gravity research, Galileo Galilei. His most famous experiment may never have happened, but his principle of inertia, law of free fall, and principle of relativity are the basis for everything that comes later in the science of gravity--including key breakthroughs by Einstein.
The Force of Creation
Use a black hole to test the laws of thermodynamics, taking a deeper look at the capacity of gravity to pull matter together and increase entropy at the same time. Probe Stephen Hawking's most surprising discovery, and then learn that the same force that pulls the apple down and steers…
Escape Velocity, Energy, and Rotation
Begin the first of several episodes that dig deeper into Newton's laws than Newton himself was able to go. In this episode, apply the key concepts of energy and angular momentum to study how gravity affects motion. As an example, use simple algebra to calculate the escape velocity from Earth.
Stars in Their Courses—Orbital Mechanics
Newton was the first to realize that objects could, in theory, be sent into orbit around Earth. Explore how this works in practice, using the ideas of energy and angular momentum to study how satellites, moons, planets, and stars move through space.
The Falling Laboratory
Einstein focused on gravity in his general theory of relativity. Hear about his "happiest thought"--the realization that a man in free fall perceives gravity as zero. This simple insight resolved a mystery going all the way back to Newton and led Einstein to the startling discovery that gravity affects light…
The Next Revolution
Survey the greatest unsolved problem in theoretical physics: the search for a quantum theory of gravity. Examine string theory, loop quantum gravity, and also entropic gravity, which suggests a revolutionary link with thermodynamics. Close the course with a deepened appreciation for the connection between everyday features of gravity and the…
Black Holes, Tides, and Curved Spacetime - Understanding Gravity Course
Gravity rules the universe. Without it, everything would dissolve into a gas of randomly interacting atoms. Yet gravity is one of the least understood forces in nature. Black Holes, Tides, and Curved Spacetime introduces you to key ideas in gravity research over the past 400 years. It's an awe-inspiring journey…
Nudge—Perturbations of Orbits
For the next three episodes, study the effects of gravity on the motions of more than two bodies. Here, see how even very small orbital changes--small perturbations--are significant. Such effects have revealed the presence of unknown planets, both in our own solar system and around other stars.
Why Study Exoplanets?
Learn about the exciting mission of exoplanetary science--the study of planets orbiting stars beyond the Sun. Review the eight planets in our solar system, which provide a baseline for understanding the more than 1,000 worlds recently discovered in our region of the Milky Way galaxy.
What Are Tides? Earth and Beyond
Trace the origin of tides to the simple fact that gravity varies from point to point in space. This leads not just to the rise and fall of the ocean, but to the gradual slowing of Earth's rotation, Saturn's spectacular ring system, volcanoes on Jupiter's moon Io, and many other…
Revolution in the Heavens
Drawing on ideas and observations of Nicolaus Copernicus and Tycho Brahe, Johannes Kepler achieved a great insight about gravity by discovering three laws of planetary motion, relating to the mathematics of orbits. The cause of planetary motion, he determined, must lie in the sun.