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# First Law of Thermodynamics introduction

AP.BIO:
ENE‑1 (EU)
,
ENE‑1.H (LO)
,
ENE‑1.H.1 (EK)
,
ENE‑1.H.2 (EK)
Energy cannot be created or destroyed. It can only be transferred or converted from one form to another.

## Want to join the conversation?

• Why can't energy be created or destroyed? Doesn't the sun create light energy or when we are coasting on a bicycle don't we create kinetic energy?
• The sun doesn't create energy. It simply chemically changes hydrogen atoms into helium atoms through a process of Nuclear Fission. The byproduct of this reaction is a massive volume of light and heat energy.

Bicycles don't create kinetic energy. We give the bike kinetic energy by pedaling the bike.
• energy can be destroyed or created.does it mean that "heat energy" can be transformed into a more useful type of energy that has the ability to do work? thus decreasing the level of entropy in the universe after all energy can be transformed from one form to another
• It depends on what you mean by 'heat energy'. If you mean there is a temperature difference between things, then yes, you can use that energy and convert it to a different form (this happens for example in a power station). However, when we talk about thermodynamics, 'heat' often describes energy lost to surroundings by increasing the random motions of molecules. Although energy can be converted from one form to another, it cannot be converted back and forth any way you want. For things to go forward, you need to have an increase of entropy in the universe (this is the second law of thermodynamics), and there is no way you could collect back all the heat energy that has been dissipated into lots of molecules. If you think about a fridge, you can decrease energy of molecules inside it, but at the cost of increasing entropy by increasing heat outside it.
• At , if the light heats up the glass bulb, then how is it intact? Shouldn't the glass overheat and explode?
• The light doesn't actually heat up anything too much, and since the glass is transparent, barely any heating will occur. The light will simply pass through the glass. If you were talking about the heat from the filament, it would disperse slowly through the collisions of molecules and get more and more dffused with each collision, so it wouldn't heat up the glass much. Even if it did, the heat would quickly disperse out through the glass, without heating it much, as Sal mentioned at .
• If energy can not be created or destroyed, what energy was there before the Big Bang?Energy has to be created,but only once.Because the energy has to be there for the big bang to happen, right?
• Well if you agree that there was absolutely nothing before the Big Bang, we may well say that none of the laws of conservation were applicable (in this context the law of conservation of energy which says energy can neither be created nor be destroyed), hence we may say that matter could be formed and that's exactly where the matter that exploded during Big Bang came from.
• what is the difference between Radiant energy & Light energy??
• Radiant energy refers primarily to energy that radiates from the source, which is commonly in the form of light energy or thermal energy, while light energy is specifically electromagnetic.
• is thermal energy and kinetic energy the same thing ?
• According to what I've read thermal energy is a somewhat ill-defined property for which usage varies.

You are correct in thinking that a significant fraction of what is usually meant by thermal energy is due to kinetic energy at the atomic level. However, kinetic energy is typically used to describe the energy associated with "organized" motion through space, while thermal energy is "disorganized" motion and also includes vibration and rotation.

An example might be if you kicked a stone out of the edge of a fire. It has kinetic energy imparted by your kick and thermal energy imparted by the fire. The thermal energy from being next to the fire is (mostly {I think}) expressed by enhanced vibration of the minerals within the rock. My understanding is that, while this thermal energy is kinetic (due to movement), it is qualitatively different from the kick imparted kinetic energy.

The following links have more details:
https://en.wikipedia.org/wiki/Thermal_energy
https://www.quora.com/Is-heat-energy-basically-just-kinetic-energy
• I had thought that einstein discovered that energy could be converted into matter, and vice versa. Does this mean that, to keep the first law of thermodynamics, all matter is a form of energy?
If this is the case, what are the implications for quantum physics? Does this have something to do with particle-wave duality?
• If energy can't be created nor destroyed than how did the energy form for the first time ?
• The conservation of energy has to do with symmetry of time invariance. The conservation of energy comes about because the laws of physics do not change based on the passage of time.

If you have an isolated closed volume of space and you take the sum of all of the energy in a volume of space at time 0s it has to match the sum of all of the energy in a volume of space at time 1s.

When we are dealing with the big bang we do not have an accurate description of the physics that were involved so the symmetry of time invariance may not hold.

Also based on the current observations of the universe and and current theories there is a way for the universe to have come into existence without requiring any energy. Just like stretching a balloon creates an amount of potential energy the stretching of spacetime is similar but with gravitation this can be offset with the introduction of mass so in the initial big bang the buildup of energy from the expansion of spacetime produced the matter and radiation we see around us.