# Pouring tea in a plane – upside down

Let me start with the video. Here is a guy flying a plane in a barrel roll and pouring some tea at the same time. Talk about multitasking. How can he pour upside down? Well, there are two ways to look at this. First, I can look at this in the frame of the plane.…

# Hey, look kids! There’s Big Ben.

And there’s parliament. Ok – sorry, I had to make a “Tom (Swans on Tea)” title for this one. Tom, forgive me. Here are two great circular motion videos. First, this one is from Dale Basler. He made himself a fine little floater-type accelerometer. Better than just make it, he made a video of the…

# MythBusters – velocity is relative

So, I complained about MythBuster’s explanation of relative velocity. How would I explain this? I would start by saying that velocity is relative. Here is the definition for velocity: I put the “avg” in there because it is more true. If the acceleration is zero, I could drop this. For the rest of this post,…

# 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…

# Fake Forces – sometimes they are Fantastic

What is a fake force? A fake force is one of those forces that introductory texts tell you aren’t real – like centrifugal force. They aren’t real in the sense that they are due to one of the fundamental interactions. Basically, introductory texts (and even blogs like this one – not a bad summary of…

# Centripetal Force, Centrifugal Force – what’s the deal?

A couple of commenters expressed concern over the use of centrifugal force after my rant on the use of the word force. So, what is the deal with these two terms? Are they ok to use? Are they real forces?

# Fake vs. Real Forces

In this post, I am going to talk about real and not real forces as well as the fake centrifugal force (if you don’t like the word “fake” you could replace that with “fictitious”) First, an example: suppose you are in a car at rest and press the gas pedal all the way down causing…

# Gravity, Weightlessness, and Apparent Weight

In my classes, I like to bring up the question: *Why do astronauts float around in space?* The most common response to this question is that they float around because there is no gravity in space. Some people take this a small step further and say that there is no gravity in space because there…