Potential Energy and Total Energy Negative

In summary, potential energy and total energy can be either positive or negative because they are measured with respect to a reference point. In the case of potential energy, it is measured with respect to a reference point of infinity, while total energy is the sum of kinetic energy and potential energy. Kinetic energy is always positive because it is measured using the square of velocity, while potential energy can be negative depending on the reference point.
  • #1
Jordash
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Homework Statement



Explain why it is possible for potential energy and total energy to be either positive or negative, but kinetic energy is always positive

Homework Equations





The Attempt at a Solution



I'm thinking that Potential Energy and Total Energy can be opposite and take away from each other, so they would be negative to subtract, but not sure how to think this one through.
 
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  • #2
Potential energy is measured with respect to a reference point.
For example, in PE = mgh, the PE depends on the h and where it is measured from. If you take ground level to be h = 0, then you have negative PE as soon as you go down below the surface.

The potential energy of an electron in an atom and of a satellite in orbit is measured with a reference point of infinity, so these energies are always negative. Believe it or not, infinite distance is the simplest reference level, because it is the only level that is common to all atoms or planets.
 
  • #3
Ok, that makes sense, what does it mean when it says Total Energy? I think it means

E=KE+PE
E=1/2mv^2+mgh

So Total Energy can be negative because Potential Energy can be negative, is that right?
 
  • #4
Also, look at your equation for kinetic energy: (0.5)*(m)*(v^2) - can any of these variables be negative?
 
  • #5
well velocity could be I guess but it's square so it will always be positive.
 
  • #6
Exactly! So then, can Kinetic energy EVER be negative?

Now look at the equation for potential - what can be negative there, and can it make the whole value negative?
 
  • #7
no never, thanks for the help!
 
  • #8
No problem! Physics Rules!
 

1. What is potential energy?

Potential energy is the energy an object possesses due to its position or state. It is a form of stored energy that can be converted into other forms of energy, such as kinetic energy, when the object is in motion.

2. How is potential energy different from kinetic energy?

Potential energy is energy that is stored, while kinetic energy is energy that is in motion. Potential energy can be converted into kinetic energy, and vice versa, but they are two distinct forms of energy.

3. What is total energy negative?

Total energy negative refers to the total energy of a system being less than zero. This can occur in certain systems, such as gravitational or electric potential energy, where the energy is negative due to the chosen reference point.

4. How is total energy negative possible?

Total energy negative is possible because energy is a relative quantity. The reference point or zero energy point chosen for a system can affect the sign of the total energy. In some systems, the reference point may be chosen in a way that results in a negative total energy.

5. What are some real-life examples of potential energy?

Some examples of potential energy in everyday life include a stretched rubber band, a compressed spring, a book resting on a shelf, and a roller coaster at the top of a hill. These objects have potential energy because of their position or state and can release this energy when they are in motion.

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