# Energy and Force: Is it Possible?

• ahyaa
In summary: So in summary, it's possible for a system to have energy without an associated force, but it's not possible to have net forces acting on a system without a net energy change. Thanks for the conversation!
ahyaa
Hello all,

I was wondering if it was possible to have energy without an associated force. More specifically, can there be an energy change in a system without a net force? From what I know, this SHOULD be impossible because energy is the integral of the work function which depends on force. On the other hand, would it be correct to say it is possible to have net forces acting on a system with no net energy change?

ahyaa said:
Hello all,

I was wondering if it was possible to have energy without an associated force. More specifically, can there be an energy change in a system without a net force? From what I know, this SHOULD be impossible because energy is the integral of the work function which depends on force. On the other hand, would it be correct to say it is possible to have net forces acting on a system with no net energy change?
You can have energy without an associated force. But, at the macroscopic level at least, work cannot be done with that energy without a force being applied through a distance.

At the quantum level it gets a little murky. The concept of force is not as clear. For example, when an atom absorbs or emits a photon, there is a change in momentum of the atom corresponding to the momentum of the photon emitted or absorbed. But if you contemplate that change being caused by a Newtonian force of the photon on the atom one would have to find that there is a force applied by the atom to the photon. But, unfortunately, the Newtonian concept of force does not really apply to a photon.

AM

ahyaa said:
Hello all,

I was wondering if it was possible to have energy without an associated force. More specifically, can there be an energy change in a system without a net force? From what I know, this SHOULD be impossible because energy is the integral of the work function which depends on force. On the other hand, would it be correct to say it is possible to have net forces acting on a system with no net energy change?

Show example where you think such a thing is possible.

Zz.

Andrew Mason said:
But if you contemplate that change being caused by a Newtonian force of the photon on the atom one would have to find that there is a force applied by the atom to the photon. But, unfortunately, the Newtonian concept of force does not really apply to a photon.

AM

Wow, interesting, thanks!

ZapperZ said:
Show example where you think such a thing is possible.

Zz.

I think I should have re-phrased my original post; I was wondering if it's possible for a system to have an energy change WITHOUT a net force acting over a distance.

I actually don't have my own example of where that would be possible, I was just purely curious.

Some scenarios that did make me think of this:

1) A figure skater pushes off a wall (the system: figure skater and wall). A normal force is exerted on her by the wall, yet no work is done on her by the wall, because there is no displacement of her hands at the same time the normal force of the wall pushes on her hands. Although there is no net work done by the wall, I learned that for this scenario, there is still an energy change associated with the wall's normal force. The energy change here is that of chemical energy the skater metabolizes into kinetic energy.

So, in this scenario, if I'm analyzing this correctly, there's work done by the skater because there's no displacement of the skater's hands, which is the object on which the wall's normal force acts. This is pretty intuitive.

2) Another scenario is in thermodynamics - a change in thermal energy. However, I know that thermal energy is caused by collisions of particles, which exert forces on each other during momentary 'inelastic' periods of their collisions. So there are atomic "normal forces" on each other when two particles of different speeds collide. Thus changes in thermal energy are due to these collisions, so there are still forces acting here even though it's not obvious.

So, other than what Andrew Mason presented I wouldn't have any actual cases in which there would be no energy change associated with a force*displacement.

I can confirm that it is not possible to have energy without an associated force. Energy and force are closely related and cannot exist without each other. In physics, energy is defined as the ability to do work, and work is defined as the product of force and displacement. Therefore, any change in energy requires the presence of a force.

However, it is possible to have net forces acting on a system with no net energy change. This can occur when there are equal and opposite forces acting on an object, resulting in a balanced system and no overall change in energy. An example of this is when an object is at rest on a surface, where the force of gravity is balanced by the normal force exerted by the surface.

In conclusion, energy and force are intertwined concepts and cannot exist independently. Any change in energy requires the presence of a force, but it is possible for a system to have net forces with no net energy change. Further research and experimentation may provide more insight into the complex relationship between energy and force.

## 1. What is the relationship between energy and force?

Energy and force are closely related concepts in physics. Energy is the ability to do work, while force is a push or pull that causes an object to accelerate. In other words, force is what transfers energy from one object to another. Without force, energy cannot be transferred, and without energy, there can be no force.

## 2. Is it possible to create energy from nothing?

According to the law of conservation of energy, energy cannot be created or destroyed, it can only be transformed from one form to another. This means that it is not possible to create energy from nothing. However, it is possible to convert one form of energy into another, such as converting chemical energy into electrical energy in a battery.

## 3. Can energy or force be destroyed?

Similar to the previous question, energy and force cannot be destroyed. They can only be transformed or transferred from one form to another. For example, when a moving object collides with another object, its kinetic energy is transferred to the other object, causing it to move.

## 4. How do energy and force affect motion?

Energy and force play a crucial role in determining an object's motion. Force causes an object to accelerate, while energy is what allows the object to maintain its motion. The amount of force and energy involved can affect the speed, direction, and overall motion of an object.

## 5. Can energy and force be measured?

Yes, energy and force can be measured using various units. The standard unit for measuring energy is the joule (J), while force is measured in newtons (N). Other units, such as calories and foot-pounds, can also be used to measure energy and force. Scientists use different instruments and techniques to accurately measure these quantities in different systems and scenarios.

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