gravity

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Category archives for gravity

Maybe you have noticed how much material there was (for me at least) in last week’s MythBusters. One of the myths they looked at was the bus jumping over a gap in the road from the movie Speed. I am not looking at that myth, it has been discussed many times in many places. Rather,…

Uncertainty and Video Analysis

This is for commenter JimP. How do you take into account uncertainty when using video analysis? A great question. The first thing to think about is where does the uncertainty come from? My first guess would that it would be from the user. Where does the user click? Is it right on the object in…

Fake Videos Presentation

I put together this short presentation on fake videos for a class. What the heck, I will also put it online so that maybe some other people can use it. So, here it is. I have it in many forms. First, a video of me going through the talk. Then I have the keynote and…

There were a couple of things that bothered me about the MythBusters’ myth where they fired bullets in the air. The myth was that a bullet fired in the air could kill you. The first problem is that it is not a myth. There are several reported cases of people being killed from bullets that…

Parkour Physics: Wall Climb

Forgive me if I don’t know the official parkour term for this move. This is where you have two walls that are close to each other and you vertically climb them. Here is a shot of Mark Witmer (from Ninja Warrior) doing the wall climb. Doesn’t look too hard, does it? Well, I think it…

The vomit comet bus

Check this out (saw it on the interwebs): It’s this video inside a bus of a girl hitting the roof. My first thought was: well, she just jumped. But something was odd. She was in the air too long. Well, of course this calls for a video analysis (using Tracker Video Analysis). Actually, it is…

Tides. Why are they so hard?

Every introductory astronomy text and most intro physics texts talk about tides. The usual explanation is something along the lines of: The moon exerts a gravitational force on the Earth and all the stuff on the Earth. This force decreases with distance (1/r2). Thus the moon pulls greater on one side of the Earth than…

Elephants can’t jump. Really.

Sciencegeekgirl is blogging from the AAPT. She talks about showing something interesting to get students thinking, and here is her example: This reminds me of Dan Meyer’s What Can You Do With This stuff. Anyway, I can’t help it. I must analyze this video. Plus, Fran essentially threw down the gauntlet and called me out…

Yesterday, I uploaded a post from my old site about slowing down time to make videos look like they were on the moon. If you haven’t read that, the short story is that it doesn’t look right when speed Apollo videos up so that the acceleration is -9.8 m/s2. What started that whole thing was…

Note: This is a repost from my old site. Time to move it over. First, what is different about motion on the moon and on Earth? Since the moon has a smaller mass in spite of its smaller size*, the moon has a smaller gravitational field. The gravitational field on the surface of the moon…