You are here:

Physics/Work

Advertisement


Question
Sir,

I lift a box to my waist level,,say h meters..work done is mgh...then I start to walk.Text book says that no work is done on the box..but I am walking(effort / work) is put in. I move..so work is done..force*distance moved...right? So how come text book say no work is done ?In order for the box to move(horizontally) I must push on it with my body..isn't that a force..if then I move X meters..isn't work done= F*x?

I understand the scalar dot product rule..but intuitively it doesn't make sense to me. Please help. Thanks!!

Answer
If you accelerate the box horizontally, then work is done.  The textbook is assuming you moved horizontally at infinitesimal velocity.  By "infinitesimal," I mean that you applied almost no force to get it up to a bare minimum of speed, which then carried it in an absolutely smooth way to its destination.  In real life, we know this is impossible and you do work in the physical process of taking steps to move a box, but textbook examples are generally idealized.

Physics

All Answers


Answers by Expert:


Ask Experts

Volunteer


Dr. Stephen O. Nelson

Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

©2016 About.com. All rights reserved.