Real Answers to Ridiculous Questions

Randall Munroe, author of the ever-popular geeky stickman webcomic XKCD, is also a physics & math nerd. So he gets a lot of weird hypothetical questions from his readers. Now he’s starting to answer them, and it’s pretty entertaining.

Here’s a snippet from his first question, What would happen if you tried to hit a baseball pitched at 90% the speed of light?

“After about 70 nanoseconds the ball arrives at home plate. The batter hasn’t even seen the pitcher let go of the ball, since the light carrying that information arrives at about the same time the ball does. Collisions with the air have eaten the ball away almost completely, and it is now a bullet-shaped cloud of expanding plasma (mainly carbon, oxygen, hydrogen, and nitrogen) ramming into the air and triggering more fusion as it goes. The shell of x-rays hits the batter first, and a handful of nanoseconds later the debris cloud hits.”

Seven Minutes of Terror

In November of last year, NASA launched a rocket carrying a brand new Mars rover. Dubbed Curiosity, it is five times larger than the two previous rovers (Spirit and Opportunity) and is scheduled to land on August 6 of this year.

As with everything NASA does, the Mars missions might seem a bit underwhelming at this point. After all, they’ve done it before, right? How hard can it be?

Well, aside from the fact that Mars is currently 200 billion kilometers away from the Earth (and that changes each day, as the two planets orbit the sun at different rates) through an endless ocean of empty space, there’s also the problem of successfully landing a robot onto the planet’s surface.

In this video, the team that designed Curiosity’s landing system discusses just what makes this so difficult to achieve:


What is Time?

You might have noticed that we’re slowing down the posts here at Pop Physics HQ. That’s because summer is in full, sweaty swing, the students are busy forgetting everything they’ve learned sitting at their school desks, and I want to make sure this site’s got some momentum when we pick up the pace again in September.

But the public demands more. With that in mind, here’s a good article about the basic ways physicists think about Time, written by author Paul Davies. I’ll be talking about some of these ideas in greater detail in later chapters.

“Thinking of past and future brings us to another problem that has foxed scientists and philosophers: why time should have a direction at all. In every day life it’s pretty apparent that it does. If you look at a movie that’s being played backwards, you know it immediately because most things have a distinct time direction attached to them: an arrow of time. For example, eggs can easily turn into omlettes but not the other way around, and milk and coffee mix in your cup but never separate out again.”

Read the full article here!

Mythbusters: Sail on a Boat

Back in the section on Newton’s First Law, I mentioned one of the classic examples of internal forces: a fan on a sailboat. It has since been pointed out to me a few times, usually in a somewhat smug and conclusive tone of voice, that Mythbusters busted that myth a long time ago.

mythbusters episodes
Smugly awesome.

So why did their boat go forward, as in the video below? I’m a big fan of the show, but I do think Grant’s explanation (at around 4:16) is a bit misleading.


TEDx Talk: How to Save the Earth from Asteroids

Here’s a TEDx Talk by astronomer Phil Plait (who also blogs for Discover Magazine at Bad Astronomy) about some of the asteroids that have already collided with Earth and what we can do if another big one heads our way.

He briefly mentions the fact that blowing the thing up with a nuclear bomb (as in the movie Armageddon) would probably be useless. This was expanded on in a video featuring Neil deGrasse Tyson,1 wherein he explained that if you blow up an asteroid the size of Texas that’s heading towards the Earth, chances are you’ll just end up with two half-Texas-sized asteroids heading towards the Earth.

  1. I think; but even if it wasn’t him, it’s a good default answer.

Feynman on Explaining Physics

Here’s a video of physicist Richard Feynman describing why it can be problematic to use physics to “explain” phenomena. It takes him a while to get to the point he’s trying to make, but I recommend that you stick around until the end.

The goal of physics is to answer “why” at deeper and deeper levels. Some of my favourite moments as a teacher have been ones where a student has continued to ask me why something is the case, and I keep answering until together we reach the horizon of our current knowledge about the universe. Why does matter resist acceleration? Why does time flow forwards but never back? We may never know, but we can keep digging — at least until we’ve found what seems to be a truth that lacks any possible explanation for why it is true.