# Stupid questions physics majors might ask

#### anton717

But what kind of energy does a particle possess at 0 height?

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#### Chestermiller

Mentor
But what kind of energy does a particle possess at 0 height?
Can you be more specific?

Chet

#### Borek

Mentor
Height of 0 relative to what?

You have not said anything about whether the object is in motion or not. I guess you meant it is at rest, but even then question about "at rest relative to what" would be still an important one.

#### anton717

Height of 0 relative to what?

You have not said anything about whether the object is in motion or not. I guess you meant it is at rest, but even then question about "at rest relative to what" would be still an important one.
The particle is not in motion, it's at rest. And I meant to word it as RELATIVE to the Earth's surface.

#### anton717

Can you be more specific?

Chet
When a particle is at certain height (at rest) it has Potential Energy, when a particle is in motion, let's say, on the earth's surface it has Kinetic Energy, but what about a particle is at rest and on the surface of the Earth? Does it have any kind of energy stored? I am not into physics so my questions may not be clear.

#### mfb

Mentor
When a particle is at certain height (at rest) it has Potential Energy, when a particle is in motion, let's say, on the earth's surface it has Kinetic Energy, but what about a particle is at rest and on the surface of the Earth? Does it have any kind of energy stored? I am not into physics so my questions may not be clear.
It still has potential energy. Its value is zero if you define potential energy relative to the surface of earth (this is a purely arbitrary definition).
It has thermal energy and chemical energy.
It has energy from its rest mass.

#### BobG

Homework Helper
When a particle is at certain height (at rest) it has Potential Energy, when a particle is in motion, let's say, on the earth's surface it has Kinetic Energy, but what about a particle is at rest and on the surface of the Earth? Does it have any kind of energy stored? I am not into physics so my questions may not be clear.
At rest relative to the Earth's surface? Then the difference between the potential energy of the particle and the potential energy of the Earth's surface is zero. The difference between the particle's kinetic energy and the kinetic energy of the Earth's surface is zero. (Technically, the particle could have internal kinetic energy due to heat or chemical energy, but that's irrelevant in the given context.)

You're always measuring the energy of an object relative to the energy of something else. In your example, I'd assume the surface of the Earth is your "origin" - what you're comparing your energy levels to. But if you were using the center of the Earth as your "origin", both the particle and the surface of the Earth would have potential energy and kinetic energy. They'd both just have the same of each.

#### nuuskur

Why does a cat always land on its paws? Does the cat rotate itself somehow through mid air?

#### Pythagorean

Gold Member
Why does a cat always land on its paws? Does the cat rotate itself somehow through mid air?
Yes, and it uses its tail and conservation of angular momentum! I guess it's body distortions are probably more relevant than its tail in conservation.

#### mfb

Mentor
I guess it's body distortions are probably more relevant than its tail in conservation.
Right. The tail might have some stabilizing/control function, but cats can rotate without it in the same way they can do it with tail.

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