Comments on: First year physics was a long time ago. http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/ Tales from Greg and Kat, in NC and elsewhere. Thu, 29 Sep 2011 23:17:09 +0000 hourly 1 http://wordpress.org/?v=3.3.1 By: Gordon http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/comment-page-1/#comment-4142 Gordon Fri, 02 Nov 2007 22:50:13 +0000 http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/#comment-4142 I remember a display at the PNE one year. There was a bicycle on friction rollers which people would expend energy to see how much food they could eat extra because of that workout. People would peddle hard for 10 or 15 minutes and the person in charge of the display would inform them that they could now go eat a low single digit number of greesy french fries (usualy between 0.5 and 3). Without factoring in the inefficiency of the human body and the energy expended making bodily power available to the muscles you can end up with very small amounts of energy resulting from equations. I wonder if anyone has measured the amount of gasoline it takes to go up the hill. I remember a display at the PNE one year. There was a bicycle on friction rollers which people would expend energy to see how much food they could eat extra because of that workout. People would peddle hard for 10 or 15 minutes and the person in charge of the display would inform them that they could now go eat a low single digit number of greesy french fries (usualy between 0.5 and 3).

Without factoring in the inefficiency of the human body and the energy expended making bodily power available to the muscles you can end up with very small amounts of energy resulting from equations.

I wonder if anyone has measured the amount of gasoline it takes to go up the hill.

]]> By: Ted Kirkpatrick http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/comment-page-1/#comment-3733 Ted Kirkpatrick Sat, 08 Sep 2007 19:46:00 +0000 http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/#comment-3733 1. Let's all use the SI units correctly. The proper measure of human exertion is neither calories nor Calories, nor nigiri, nor Big Macs, but beers. 2. In addition to bicycling, how many calories do you spend blogging? Perhaps if you take the bus, thereby arriving at work faster than if you biked, giving you more time to blog, you'd actually earn more beers! Thanks to Brian for his analysis. Like Greg, I'd wondered what I might be gaining from crawling up the Hill. Ted (Who didn't bike to work today, but tries to during the regular week...) 1. Let’s all use the SI units correctly. The proper measure of human exertion is neither calories nor Calories, nor nigiri, nor Big Macs, but beers.

2. In addition to bicycling, how many calories do you spend blogging? Perhaps if you take the bus, thereby arriving at work faster than if you biked, giving you more time to blog, you’d actually earn more beers!

Thanks to Brian for his analysis. Like Greg, I’d wondered what I might be gaining from crawling up the Hill.

Ted
(Who didn’t bike to work today, but tries to during the regular week…)

]]> By: Kat http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/comment-page-1/#comment-3677 Kat Wed, 05 Sep 2007 22:04:00 +0000 http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/#comment-3677 See! So you DO have to factor in forward motion in the form of distance traveled! HAH! You rock Brian!!!! Must be your lifestyle (rock and roll) :P See! So you DO have to factor in forward motion in the form of distance traveled! HAH!

You rock Brian!!!! Must be your lifestyle (rock and roll) :P

]]> By: Brian http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/comment-page-1/#comment-3672 Brian Wed, 05 Sep 2007 16:42:37 +0000 http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/#comment-3672 Yeah, I always hated when my professors told me if I carried a 200lb block around in a circle I would have done no work. They said the same thing if I spent a week working on a single problem but didn't get the answer. This is why I am a recovering physicist--so don't assume my answer has any authoritative weight to it. So, what you've calculated is the work you've done against gravity. And, you're right, a food Calorie (capital C) is 1000 SI calories (lowercase c). Gravitational potential energy is conserved, so, if you turn around at the top of the hill and coast back down, do you put back on those 37 Calories? No, you've converted gravitational potential energy to kinetic energy. And that's where the rest of your workout comes from. You're taking a bike that would be perfectly happy sitting still, and you're propelling it along the road, increasing its (and your) kinetic energy. You're applying force to the pedals, which imparts force to the wheels, which exert force on the ground, which pushes back, propelling the bike forward. There's also friction in the system, which usually gets swept under the rug in most physics classrooms. Let's just say if your brakes are rubbing, they're introducing more friction to the system, making it harder to push those wheels around. Incidentally, when you stop your bike, you're converting kinetic energy to thermal energy through friction, and your brake pads and wheels heat up. So, to figure out the calories in your workout, you need to integrate the amount of force your wheels exert on the ground over the distance you travel. There are special hubs you can get for your bike (PowerTap comes to mind) which measure your power output (work/time), which you can integrate over time to compute the work you've done in your workout. Yeah, I always hated when my professors told me if I carried a 200lb block around in a circle I would have done no work. They said the same thing if I spent a week working on a single problem but didn’t get the answer. This is why I am a recovering physicist–so don’t assume my answer has any authoritative weight to it.

So, what you’ve calculated is the work you’ve done against gravity. And, you’re right, a food Calorie (capital C) is 1000 SI calories (lowercase c). Gravitational potential energy is conserved, so, if you turn around at the top of the hill and coast back down, do you put back on those 37 Calories? No, you’ve converted gravitational potential energy to kinetic energy.

And that’s where the rest of your workout comes from. You’re taking a bike that would be perfectly happy sitting still, and you’re propelling it along the road, increasing its (and your) kinetic energy. You’re applying force to the pedals, which imparts force to the wheels, which exert force on the ground, which pushes back, propelling the bike forward.

There’s also friction in the system, which usually gets swept under the rug in most physics classrooms. Let’s just say if your brakes are rubbing, they’re introducing more friction to the system, making it harder to push those wheels around. Incidentally, when you stop your bike, you’re converting kinetic energy to thermal energy through friction, and your brake pads and wheels heat up.

So, to figure out the calories in your workout, you need to integrate the amount of force your wheels exert on the ground over the distance you travel. There are special hubs you can get for your bike (PowerTap comes to mind) which measure your power output (work/time), which you can integrate over time to compute the work you’ve done in your workout.

]]> By: Greg http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/comment-page-1/#comment-3585 Greg Thu, 30 Aug 2007 15:58:00 +0000 http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/#comment-3585 I don't think so. Imagine climbing a 200 m rope: that's basically what I calculated. That's going to suck pretty hard (and burn way more than 37 calories), and there's no forward motion to worry about. I don’t think so. Imagine climbing a 200 m rope: that’s basically what I calculated.

That’s going to suck pretty hard (and burn way more than 37 calories), and there’s no forward motion to worry about.

]]> By: Kat http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/comment-page-1/#comment-3583 Kat Thu, 30 Aug 2007 12:48:18 +0000 http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/#comment-3583 Don't you HAVE to account for the forward motion because that's where the friction comes from? Wait until Eastwood gets home. I'm sure he'll know... Don’t you HAVE to account for the forward motion because that’s where the friction comes from? Wait until Eastwood gets home. I’m sure he’ll know…

]]> By: Curtis http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/comment-page-1/#comment-3561 Curtis Tue, 28 Aug 2007 21:52:25 +0000 http://gregbaker.ca/blog/2007/08/26/first-year-physics-was-a-long-time-ago/#comment-3561 You weigh 80kg + bike, and you lose a lot of energy to friction, I guess? You weigh 80kg + bike, and you lose a lot of energy to friction, I guess?

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