We live our lives under the influence of the Earth's gravity, but we also know that the influence of gravity is not the same everywhere.  We can estimate the gravitational field on the surface of different planets by observing the motion of each planets' satellites (i.e. moons).

Astronauts on the moon experienced 1/6 of the normal earth gravity.
[[https://youtu.be/oYEgdZ3iEKA?si=g0tigZ65kcIshzG_|Apollo 15]]

As astronauts prepared for the Moon landings, they experienced many different conditions which impacted their normal experience of gravity.

===== Free Fall Feels Like Zero-Gravity =====

While they orbited the Earth, they were under the influence of gravity (no straight line motion, right?) but felt weightless.  We sometimes call this zero-gravity, but of course, we didn't cancel the Earth's gravitational field--we just let the astronauts "go with it".  When you think about it, we don't "feel" gravity, we feel the force that opposes gravity to keep our net force equal to zero.  We feel the contact force (or normal force) that comes from the floor, or our seat.  Take away the normal force, and we feel weightless, as you can see in the following scenarios:
  * Scenario 1: Drop Tower.  [[https://youtube.com/clip/Ugkx9OyON6cOZHvvc9O7F3RDfT8WPUantgOR?si=Qt8YDCkM5Ph12tmk|Drop Tower POV]] ; [[https://youtu.be/av-WqguS8UI?si=QCuwMheZxkTdAP__|How Drop Towers Work, Full Video (2:48)]]
  * Scenario 2: Stack of Coins. [[https://youtu.be/1xnMX5-Rcxo?si=0NfyuI4U8sTAA6sk| Full Video (1:16)]]
  * Scenario 3: Vomit Comet. [[https://youtube.com/clip/UgkxPSQ7TkYHJ-4WLuZLtQo-LY-tzxTIe4zN?si=lX9u-4p0QAQ-9k7x|NASA Mercury Training Clip]] ; [[https://youtu.be/LO1ojoKcS4U?si=3HrwTceKkfE3MoH8|Full Video (2:48)]]
  * Scenario 4: OK Go Video. [[https://youtube.com/clip/UgkxYTe-dMLd4ulpqHUCPz-vwLW1Iad6dNGH?si=aM0Bsv60LF1cOiFK|Zero-Gravity Parabola]] ; [[https://youtu.be/LWGJA9i18Co?si=1wBYZ0p745ovMnVu|Full Video (3:22)]] ; [[https://youtu.be/YwyXLBQUEC0?si=a9hgEq48PoJCJpsU|Full Documentary (19:39)]]
  * Scenario 5: 2001: A Space Odyssey. [[https://youtube.com/clip/UgkxAgfcsoQYyMqe7vo8pPl5R5S_Wg3EdFQV?si=hlo8t9LqIe8a40N-|Velcro Shoes Clip]] ; [[https://youtu.be/0ZoSYsNADtY?si=dn3h4qbxcSjtdxdq|Full "Waltz" Scene (4:20)]]
  * Scenario 6: Astrosmiles. [[https://youtube.com/clip/UgkxmfS1IBB0ZKusU9zRkFkHVgHNaS47nUmT?si=iLlYaVPif1knN9kF|Eating Clip]] ; [[https://youtube.com/clip/UgkxseCL8jr79wQSBkd4bQZKLyBEQHvsdrzP?si=R4x0lj3tkHUASDEH|M&M Clip]] ; [[https://youtube.com/clip/UgkxDqPXBf7ggbYD37Hc6WGEVdw8cgMZzGmR?si=kPnBx0GdjEwC6ZAs|Hair Wars]] ; [[https://youtube.com/clip/UgkxHTpLE__YxarNbzd13_PycmpriyFBYlyT?si=yGJnhJu_1wxtj6ll|Down, Up, Doesn't Make Any Difference]] ; [[https://youtu.be/5hNAiABnSE0?si=Bn1oo2M5iSvoS0u8|Full Video (24:52)]]
  * Scenario 7: Diving. [[https://youtu.be/slzFkEQENu0?si=dzOxSDcKQocC0Wpb|Highest Scoring Dive Ever]] ; [[https://youtube.com/clip/UgkxgKpuN31pdMy9gm44z2PjtWhJCKOd9_i4?si=OAcxo6Ezbh_n-BJw|Acrobatics Start on the Way Up (Clip)]]


===== Constant Acceleration Feels Like Gravity =====

  * Scenario 1: Rocket Sled (JP Stapp) [[https://youtu.be/HV4JzoeaWTQ?si=6VziGXTbtClyZhAL|Strapped to a Rocket, For Science]]
  * Scenario 2: Astronaut Tests [[https://youtube.com/clip/UgkxnPP6ik0zVDIX_qcT5pfD_ZIICYbbWXod?si=82XTEWVdC6_bslOP|Centrifuge Spinup]] ; [[https://youtube.com/clip/UgkxdTGsKziEEm06pabQsuPnmO1OG-Hv7Q9W?si=1cLj0L28Mon3LsLO|Different G-factors]] ; [[https://youtube.com/clip/UgkxdTGsKziEEm06pabQsuPnmO1OG-Hv7Q9W?si=1cLj0L28Mon3LsLO|Longer Documentary (4:48)]]
  * Scenario 3: Fighter Pilot Fails [[https://youtu.be/kUscr9kSgYM?si=AcmgYGnZWZm5hiRa|Footage of 7-G Buildup (3:18)]]
  * Scenario 4: 2001: A Space Odyssey (Jupiter Mission) [[https://youtube.com/clip/Ugkxiy_6bH9uP_pDcVAJNwWmUQ44tumdKjTT?si=KU8aaFVdk06MYXEv|Centrifuge (Laps)]] ; [[https://youtube.com/clip/UgkxtpZa7Zr98vaK_28GgDLozEbhtsqH3Qta?si=0AFx-zTEe8ze3X4h|Centrifuge (Axle to Ladder)]] ; [[https://youtu.be/BtC5hTt0fbc?si=rz_kkFfc5lG8VuvC|Full Scene (4:01)]]
  * Scenario 5: 2001: A Space Odyssey (Orbital Hotel) [[https://youtube.com/clip/UgkxI3Y2Q9pR7YZyv9PE-qM6d8Hx9eubK3VC?si=jW6Dm_zdajLzqhY1|Hotel Approach]] ; [[https://youtu.be/vG6CjOFlo7A?si=RxK4QwbGmetgUZ-v|Hotel Check-in]]

=====Light Beams in Gravitational Fields=====





[[https://youtube.com/playlist?list=PLxdM6s3pVhAXy7GQ-7ElO2YhjUl85HOHx&si=HaUvt5BL-TmWwfq5|Entire Equivalence Principle Playlist]]