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Types of energy

Energy and how it can change forms. Kinetic, potential, and chemical energy.


What does it mean to have energy? Well, think about how you feel when you wake up in the morning. If you have lots of energy, that probably means you feel awake, ready to go, and able to do what needs to be done during the day. If you have no energy (maybe because you didn’t get your eight hours of sleep), then you may not feel like getting out of bed, moving around, or doing the things you need to do.
While this definition of energy is an everyday one, not a scientific one, it actually has a lot in common with the more formal definition of energy (and can give you a helpful way to remember it). Specifically, energy is defined as the ability to do work – which, for biology purposes, can be thought of as the ability to cause some kind of change. Energy can take many different forms: for instance, we’re all familiar with light, heat, and electrical energy.
Here, we’ll look at some types of energy that are particularly important in biological systems, including kinetic energy (the energy of motion), potential energy (energy due to position or structure), and chemical energy (the potential energy of chemical bonds). Energy is never lost, but it can be converted from one of these forms to another.

Kinetic energy

When an object is in motion, there is energy associated with that object. Why should that be the case? Moving objects are capable of causing a change, or, put differently, of doing work. For example, think of a wrecking ball. Even a slow-moving wrecking ball can do a lot of damage to another object, such as an empty house. However, a wrecking ball that is not moving does not do any work (does not knock in any buildings).
The energy associated with an object’s motion is called kinetic energy. A speeding bullet, a walking person, and electromagnetic radiation like light all have kinetic energy. Another example of kinetic energy is the energy associated with the constant, random bouncing of atoms or molecules. This is also called thermal energy – the greater the thermal energy, the greater the kinetic energy of atomic motion, and vice versa. The average thermal energy of a group of molecules is what we call temperature, and when thermal energy is being transferred between two objects, it’s known as heat.

Potential energy

Let’s return to our wrecking ball example. The motionless wrecking ball doesn’t have any kinetic energy. But what would happen if it were lifted two stories up with a crane and suspended above a car? In this case, the wrecking ball isn't moving, but there is, in fact, still energy associated with it. The energy of the suspended wrecking ball reflects its potential to do work (in this case, damage). If the wrecking ball were released, it would do work by making a pancake of someone’s poor car. And if the ball is heavier, the energy associated with it will be greater.
Image of water held behind a dam.
Image credit: OpenStax Biology, "Dam," by Pascal.
This type of energy is known as potential energy, and it is the energy associated with an object because of its position or structure. For instance, the energy in the chemical bonds of a molecule is related to the structure of the molecule and the positions of its atoms relative to one another. Chemical energy, the energy stored in chemical bonds, is thus considered a form of potential energy. Some everyday examples of potential energy include the energy of water held behind a dam, or of a person about to skydive out of an airplane.

Energy conversions

An object's energy can be converted from one form to another. For instance, let’s consider our favorite example, the wrecking ball. As the wrecking ball hangs motionless several stories up, it has no kinetic energy, but a lot of potential energy. Once it is released, its kinetic energy begins to increase because it builds speed due to gravity, while its potential energy begins to decrease, because it is no longer as far from the ground. Just before it hits the ground, the ball has almost no potential energy and a lot of kinetic energy.
Diagram of octane, ball-and-stick model of octane, and image of a speeding racecar.
Image credit: OpenStax Biology. Lower panel, "Car," is a modification of work by Russell Trow.
The same kinds of conversions are possible with chemical energy, and we see lots of examples of this in our day-to-day lives. For instance, octane, a hydrocarbon found in gasoline, has chemical energy (potential energy) due to its molecular structure, which is shown above. This energy can be released in a car engine when the gasoline combusts, producing high-temperature gases that move the engine’s pistons and, ultimately, propel the car forward (kinetic energy)1. Part of the chemical energy is converted to the kinetic energy of the car, while part is converted to thermal energy as heat emitted from the engine.
Energy can change forms in a similar way in living organisms. For instance, energy stored in bonds of the small molecule ATP (potential energy) can power the movement of a motor protein and its cargo along a microtubule track, or the contraction of muscle cells to move a limb (kinetic energy).

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  • blobby green style avatar for user GULMEK86
    ummmm i'm still a little confuse with "thermal and kinetic energy" so thermal is a form of kinetic energy,so thermal and kinetic are the same?!
    (34 votes)
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    • piceratops seedling style avatar for user martindjenkins
      Thermal energy is energy in disorderly motion - everything is moving in random directions. When people talk about "kinetic energy", they usually mean energy in orderly motion - everything moving in the same direction. The meaning of "orderly" can be a bit subjective, usually depending on how closely you're looking at the particles.
      (27 votes)
  • mr pink red style avatar for user Thermos
    In cameras, the chemical potential energy (battery) is converted to electrical energy (camera circuit). Then, what is this electrical energy converted to when I take a photo?

    (7 votes)
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    • blobby green style avatar for user rodgw72
      In the camera, as well in many machines you don't use the electron energy, but only the energy that pushes the electrons on the pathway. The electrons are only the carriers of the energy. But the internal energies of the electrons are not used (yet). Many persons don't fit on this: electric energy is not the energy of the electron: is the kinetic energy that is transformed from waterfalls (hydrelectric), thermoelectric generators, etc, that put potential energy and the potential energy difference (Volt) to electron movements. So, the machines uses that energy transforming into its uses (mechanical movement of the obturator, the digital LCD that guide you to take a best picture, etc. But the image reception occur with other source: the photossensitivity of many microLEDs with special features of transform photonic energy into voltage (potential energy diference), and that send to the microprocessor to calculate the spatial position of each microreceptiveLED, its voltage intensity to bright. Color is a more complex understanding and I will not explain here :)
      (14 votes)
  • aqualine ultimate style avatar for user Badriya
    does ATP have kinetic or potential energy ?
    (9 votes)
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    • starky ultimate style avatar for user Greacus
      ATP has potential energy in the bonds between the phosphates. If an ATP molecule is used, one phosphate is 'broken' off and so the bond between the phosphates is broken. There was energy stored in this bond, which is then used to do numerous kinds of things in your body. This energy can be used to move things (kinetic energy).

      Hope this helps!
      (16 votes)
  • blobby green style avatar for user Tayba Buraihi
    If I light a candle but the flame isn't moving will it have kinetic or potential energy?
    (7 votes)
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  • aqualine sapling style avatar for user Annabel L
    Why can chemical energy be kinetic and potential?
    (4 votes)
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  • marcimus pink style avatar for user Reham
    Sorry I don't understand this line "Another example of kinetic energy is the energy associated with the constant, random bouncing of atoms or molecules" how it is kinetic and constant ?
    (5 votes)
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    • leafers ultimate style avatar for user Sahil
      Kinetic energy basically means movement. As the particles are in motion (which is perceived as pressure or temperature), it is considered as kinetic energy. The second part of your question can be explained by taking our own example. You and I are surrounded by air (hopefully ;) ). This air vibrates, unevenly, or evenly to produce sound in the form of kinetic energy which our ears feel. The pressure can be felt underwater or if we are in a falling motion, that is, the wind hits your face. Hope this helps ;)
      (6 votes)
  • starky ultimate style avatar for user carr14
    I am a bit lost. I'm looking for how to find the kinetic and potential energy of something. Does anyone know where to find that?
    (4 votes)
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  • marcimus purple style avatar for user oohlala
    Are there other types of energy? If they are, what are they?
    (4 votes)
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  • aqualine tree style avatar for user FlahertyJo
    How does breaking the phosphate bonds in ATP help a motor protein move? I understand that breaking the bonds "releases energy," but how does this energy work in a molecular capacity. What does it do to the components in a cell?
    (5 votes)
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  • piceratops sapling style avatar for user Den Langurayan
    is potential energy constant or can it be constant? due to gravity, wouldnt everything that has mass and takes up space has constant potential energy because technically, everything is "suspended" by the earth's layers?
    (5 votes)
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