# Inertia and my wheelbarrow **URL:** \ **Category:** Factual Questions\ **Created:** [July 29, 2009, 5:47pm UTC](https://boards.straightdope.com/t/inertia-and-my-wheelbarrow/504687 "2009-07-29T17:47:28Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [July 31, 2009, 3:17am UTC](https://boards.straightdope.com/t/inertia-and-my-wheelbarrow/504687/21 "2009-07-31T03:17:32Z")
> [@Chronos](#): > > Air resistance is going to be negligible for a wheelbarrow, though, and rolling resistance close to it unless you’ve got a flat tire. I’d agree with the air part. However, with a heavy wheelbarrow on grass and soft ground? At slow speeds it would not surprise me if that was the dominate consideration. ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [July 31, 2009, 2:49pm UTC](https://boards.straightdope.com/t/inertia-and-my-wheelbarrow/504687/22 "2009-07-31T14:49:57Z")
Another way to look at it: Work = Force x Distance (Newtonian definition of work) Change in speed = Force x Time (x a constant to account for the mass involved) So if you apply some given force for 1 second, you will increase the speed by 1 MPH regardless the starting speed. BUT if the starting speed was higher, then you covered more distance during that second, so you did more work. The above neglects friction and a number of other factors. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 31, 2009, 5:45pm UTC](https://boards.straightdope.com/t/inertia-and-my-wheelbarrow/504687/23 "2009-07-31T17:45:13Z")
> [@](#): > > Wait, I was always taught that there was no absolute frame of reference from which to measure speed (obviously, we’re talking vacuum, yada, yada, here). So, bearing that in mind, I would have thought that in that vacuum, the speed of the rocket + cube wouldn’t matter - going from X to X+1 mph is the same thing. And, yeah, forget about rocket fuel and weight and all that. Yes, but you still have to pick some particular reference frame and stick to it (or if you’re changing reference frames, take that change into account). The energy of a system and its components will be different in reference frame A from what it is in reference frame B, but in any given reference frame, it’s conserved and everything works out. What’s confusing about the rocket example is that you’re trying to use a reference frame attached to the rocket, but it’s accelerating, so it isn’t always in the same reference frame. ---
**Author:** ![runcible\_spoon](https://avatars.discourse-cdn.com/v4/letter/r/9fc29f/32.png) [@runcible\_spoon](https://boards.straightdope.com/u/runcible_spoon)\ **Post date:** [July 31, 2009, 7:49pm UTC](https://boards.straightdope.com/t/inertia-and-my-wheelbarrow/504687/24 "2009-07-31T19:49:16Z")
> [@Chronos](#): > > Yes, but you still have to pick some particular reference frame and stick to it (or if you’re changing reference frames, take that change into account). The energy of a system and its components will be different in reference frame A from what it is in reference frame B, but in any given reference frame, it’s conserved and everything works out. What’s confusing about the rocket example is that you’re trying to use a reference frame attached to the rocket, but it’s accelerating, so it isn’t always in the same reference frame. Ah, that makes more sense. I still have no idea what’s going on, but at least now I know why. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [August 1, 2009, 2:38am UTC](https://boards.straightdope.com/t/inertia-and-my-wheelbarrow/504687/25 "2009-08-01T02:38:45Z")
> [@Joe Frickin Friday](#): > > It doesn’t just appear to be doing twice as much work, it actually _is_ doing twice as much work. […] In your scenario, that second winch brake will heat up twice as quickly as the first winch brake. It’s not doing twice as much work. It is only doing twice as much work specifically to its winch brake. It’s doing much less work to the rest of its environment, by virtue of leaving exhaust gasses that are traveling backwards more slowly. There are a few different buckets to keep track of here. When you keep track of them all, both rockets do the same amount of work. They have to. They are converting the same amount of chemical potential energy into heat and motion in the same end products. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [August 1, 2009, 3:10am UTC](https://boards.straightdope.com/t/inertia-and-my-wheelbarrow/504687/26 "2009-08-01T03:10:31Z")
> [@Napier](#): > > It’s not doing twice as much work. It is only doing twice as much work specifically to its winch brake. It’s doing much less work to the rest of its environment, by virtue of leaving exhaust gasses that are traveling backwards more slowly. There are a few different buckets to keep track of here. When you keep track of them all, both rockets do the same amount of work. They have to. They are converting the same amount of chemical potential energy into heat and motion in the same end products. We’re saying the same thing, but you’re right, I should have been more specific: the faster rocket is doing twice as much work _to its vehicle_ as the slower rocket is to its (slower) vehicle. [Previous page](https://boards.straightdope.com/t/inertia-and-my-wheelbarrow/504687.md?page=1)