Physics Phriday: Measuring the Speed of Light

The speed of light is fast, really fast.  How can you measure something that travels at almost 300,000 km/s (186,000 miles/second)?  Galileo, a pretty smart guy, first tried in 1638 and concluded that light traveled “fast” (I told you he was smart).  It wasn’t until almost 40 years later that someone found a reasonable value for the speed of light.  This article is a history of the measurement of the speed of light.

Read More: Speed of Light Measurement

Physics Phriday: How Do Rechargable Batteries Work?

We’ve talked a lot about batteries in class, but most of the time we were talking about standard batteries.  One of the most common types of batteries that you use in your daily life is rechargeable batteries.  Here’s a video showing how they work.

Meteor Explodes Over Russia

A meteor exploded over Russia last night.  It’s still too early to be sure of what happened, but it appears that the meteor split and exploded while very high up.  I’m sure scientists are rushing to find any pieces that fell to the ground so they can figure out what type it was and where it came from.  This is probably unrelated to the asteroid that is passing by today because they were moving in different directions.  Quite the cosmic coincidence!  Here are some amazing videos of the event.

From the dashboard camera in someone’s car:

Here, someone started videoing the smoke trail and caught the sonic boom at about 25 seconds into the video.  It was loud enough to break windows and set off car alarms.

In these, the sonic boom is right at the beginning.  In the second video you can hear glass breaking.

Physics Phriday: A Near Earth Asteroid

From the Bad Astronomer:

On Friday, Feb. 15, the Earth is going to get a very close shave by an asteroid. Called 2012 DA14, this 50 meter (160 foot) rock will pass just over 27,000 kilometers (17,000 miles) from the Earth’s surface. This is closer than our geosynchronous satellites, so this really is a close pass!

But, to be very clear: This asteroid poses no threat to us right now, nor in the foreseeable future. Friday’s miss is just that: a miss. And, in fact, this is a good thing, since any time an asteroid gets close (but misses), we learn a lot, including how to find them, how to track them, and even how to talk about them to the public.

So let me tell you all about this little rock, and why it’s so cool.

Physics Phriday: How a Lead-Acid Battery Works

We’ve been talking a lot about batteries recently, but they’re still a bit of a magical device to most people.  In this video, you are shown the insides of a motorcycle battery (like a small car battery) and told how it works in more detail than we discussed in class.

Physics Phriday: How Do Cats Land on Their Feet?

Everyone knows that cats always land on their feet.  When they are dropped upside down from a height of at least 30 cm they can flip themselves over in mid-air so they land on their feet.  Keep in mind that falling from 30 cm up gives the cat only 0.25 seconds to get their feet under them before they hit the ground.  It’s also been documented (by vets in NY studying cats who have fallen out of high rise apartments) that injury rates per cat increased in falls of up to 7 stories, but decreased as they fell from higher than 7 stories.  The likely explanation is that the cats reach terminal velocity after a 7 story fall and start to relax and spread out like a skydiver, which slows them down and lessens their chance of injury.  One cat in Boston fell from the 19th story and merely chipped a tooth.  The highest fall I could find where the cat survived was from 32 stories up!

Here is a high-speed video of the cat righting reflex in action.  These cats look pretty compliant.  One of my cats would probably let me do this… once, but the other would scratch my face off if I tried to hold her upside down!