Unlocking the Mystery: Exploring the Missing Energy in a Stretched Wire

  • Thread starter Iamtoast
  • Start date
  • Tags
    Energy
In summary: Thanks for the heads up!In summary, the mass lost energy due to the c of g difference and the gradual lowering of the mass.
  • #1
Iamtoast
8
0

Homework Statement



Perhaps a more provocative title will engage readers:

I am in the vacuum of space. I carefully load a wire with a mass of 8kg, supporting the mass all the while with my hand. The wire stretches by 4.2 cm. What is the potential energy stored by the wire? What is the loss of potential energy of the mass?

Homework Equations



energy stored in the wire = work done in stretching the wire = 1/2 F.x
gpe lost by mass = mgh


The Attempt at a Solution



energy stored in the wire = work done in stretching the wire = 1/2 F.x = 1/2 mgx = 1.65 J
gpe lost by mass = mgh = 3.3 J

The wire gains exactly half the energy lost by the mass. A curious result. And it is not only the mass that loses energy. The wire's c of g is also lower and hence the wire loses gpe. My hand is also lower than at the start and loses gpe. The wire was loaded so carefully that there was no perceptible rise in temperature of any part of the apparatus. Where has my missing energy gone?
 
Physics news on Phys.org
  • #3
Iamtoast said:

Homework Statement



Perhaps a more provocative title will engage readers:

I am in the vacuum of space. I carefully load a wire with a mass of 8kg, supporting the mass all the while with my hand. The wire stretches by 4.2 cm. What is the potential energy stored by the wire? What is the loss of potential energy of the mass?

Homework Equations



energy stored in the wire = work done in stretching the wire = 1/2 F.x
gpe lost by mass = mgh


The Attempt at a Solution



energy stored in the wire = work done in stretching the wire = 1/2 F.x = 1/2 mgx = 1.65 J
gpe lost by mass = mgh = 3.3 J

The wire gains exactly half the energy lost by the mass. A curious result. And it is not only the mass that loses energy. The wire's c of g is also lower and hence the wire loses gpe. My hand is also lower than at the start and loses gpe. The wire was loaded so carefully that there was no perceptible rise in temperature of any part of the apparatus. Where has my missing energy gone?

I suggest the following experiment:
Place perhaps 20 large rocks, cinderblocks, bags of sand, whatever on an elevated shelf, table, wall so that they are perhaps 50 cm or more above the floor.

Then allow them to sit quietly while you rest and put on clothing that is just a little warm for the ambient temperature.

Then lower each object smoothly to the ground, making sure none hit the ground with any appreciable speed. Don't pause till all are down.

Did any part of the system experience a temperature rise? If you're not sure, repeat with 100 objects (or have your weight-lifter brother keep replacing the objects back on the shelf).
 
  • #4
It's sweaty work! Would the increase in humidity contribute to temperature change?

Also, every object has to be lowered infinitely slowly...Otherwise the whole process has to be repeated until it's perfected.
 
  • #5
That is like one of those old movies where the cops find a message written on a bathroom mirror with lipstick,
"Stop me before I pun again"

Wish I had said it.
 
  • #6
Thanks y'all

Thank you TVP (textured vegetable protein?) 45 and Shooting Star. I like your response and the gently mocking humour with which it is laced. Priceless.
 
  • #7
But I do hope you also got a qualitative idea about the problem that you had posed.
 
  • #8
By the way, you could do your experiment with a constant force spring where, in the ideal case, the mass could be lowered by a baby's breath on it, and you would have no "missing energy". The equations come out a little different for constant force springs of course.

TVP (textured vegetable protein?) Ah, you've seen my latest brain MRI?
 

1. What is the "missing energy" in a stretched wire?

The "missing energy" in a stretched wire refers to the difference between the amount of energy put into the wire and the amount of energy that can be accounted for through stretching and deformation. This phenomenon has puzzled scientists for many years and has yet to be fully understood.

2. How is this "missing energy" measured?

The "missing energy" can be measured through various methods, such as using strain gauges to measure the amount of energy absorbed by the wire during stretching, or using energy balance equations to compare the amount of energy put into the wire to the amount of energy that can be accounted for through stretching and other known factors.

3. What are some potential explanations for the "missing energy" in a stretched wire?

Some potential explanations for the "missing energy" in a stretched wire include the generation of heat due to friction, the release of energy through sound waves, and the conversion of energy into other forms, such as elastic potential energy. However, none of these explanations fully account for the amount of missing energy.

4. Why is it important to understand the "missing energy" in a stretched wire?

Understanding the "missing energy" in a stretched wire is important for a variety of reasons. It can help us better understand the fundamental principles of energy and how it behaves in different systems. It can also have practical applications in fields such as material science and engineering, where the ability to accurately predict and account for energy loss is crucial.

5. What are some current research efforts focused on unraveling the mystery of the "missing energy" in a stretched wire?

There are ongoing research efforts in various fields, such as physics, materials science, and engineering, focused on understanding the "missing energy" in a stretched wire. Some studies are exploring new ways to measure and analyze energy loss in wires, while others are investigating the underlying mechanisms behind energy dissipation in stretched materials. These efforts are crucial in advancing our understanding of this intriguing phenomenon.

Similar threads

Replies
44
Views
3K
  • Introductory Physics Homework Help
Replies
2
Views
1K
  • Introductory Physics Homework Help
Replies
2
Views
2K
Replies
16
Views
2K
  • Introductory Physics Homework Help
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
7
Views
4K
  • Introductory Physics Homework Help
Replies
9
Views
4K
Replies
6
Views
2K
  • Introductory Physics Homework Help
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
6
Views
4K
Back
Top