# What Two Things Make Potential Energy?

Potential energy is the stored energy or latent energy that an object has due to its position or state. For example, a ball held up in the air has gravitational potential energy due to the pull of gravity on the ball. Similarly, a compressed spring has elastic potential energy due to the compression. In both cases, this potential energy can be converted into kinetic energy if released.

We encounter potential energy in everyday life quite frequently. For instance, holding a book up high to place it on a shelf gives it gravitational potential energy that can be released as the book falls. Stretching a rubber band gives it elastic potential energy that can propel an object when released. Winding a watch stores potential energy in the spring, which is slowly released to power the watch. Food contains chemical potential energy that our bodies convert into kinetic energy to move and function. Understanding the role of potential energy helps explain how many objects in our world work.

## Gravitational Potential Energy

Gravitational potential energy describes the energy an object possesses when elevated against the force of gravity. When an object is raised higher above the ground or a reference point, it gains gravitational potential energy equal to the work done to raise it. The gravitational potential energy (U) of an object near Earth’s surface can be calculated using the formula:

U = mgh

Where m is the mass of the object, g is the gravitational acceleration (9.8 m/s2 on Earth), and h is the height of the object above the reference point. This formula shows that an object’s gravitational potential energy increases linearly with height. Doubling the height will double the gravitational potential energy.

Some examples of gravitational potential energy in everyday life include:

• A book held 1 meter above the ground has more gravitational potential energy than when it is sitting on a table.
• A hiker climbing a mountain gains gravitational potential energy with every step up in elevation.
• Water held behind a dam has gravitational potential energy that can be converted to hydroelectric power as it flows down through the dam.
• A skier at the top of a ski slope has more gravitational potential energy than at the bottom. This potential energy is converted to kinetic energy as the skier descends.

In each case, the higher elevation corresponds to greater potential energy that can be converted into kinetic energy when the object falls.

## Chemical Potential Energy

Chemical potential energy is the potential energy stored in the bonds between atoms and molecules. It is the energy released when a chemical reaction occurs. For example, the food we eat contains chemical potential energy that is released when we digest it. Batteries also contain chemical potential energy in the form of chemical reactants that can produce electricity. Other examples of chemical potential energy include gasoline, propane, and other fuels.

Chemical potential energy exists in the bonds holding atoms together in molecules and compounds. Breaking these bonds requires energy, which can then be released as kinetic energy. For instance, digestion breaks down nutrients, releasing energy stored in their molecular bonds. Burning gasoline ignites a chemical reaction that releases energy from the fuel’s hydrocarbon molecules.

The amount of chemical potential energy stored in a substance depends on the types of atoms, the structure of their molecular bonds, and how they interact. Substances with strong molecular bonds that require a lot of energy to break, like gasoline, tend to store more potential energy.

Chemical potential energy is an important source of energy for human activities. Batteries, fuels, and food all contain chemical potential energy that can power mechanical work and electricity generation. Understanding chemical potential energy led to key innovations like internal combustion engines and lithium-ion batteries.

## Elastic Potential Energy

Elastic potential energy is the energy stored in elastic materials that are stretched or compressed. Some common examples of elastic potential energy include:

• A stretched rubber band. The atoms and molecules in the rubber band get stretched apart from their equilibrium position when the rubber band is stretched. When released, the rubber band contracts and the elastic potential energy gets converted into kinetic energy.
• A compressed spring. Compressing a spring pushes the coils together so they are squished. The compressed coils want to spring back to their natural length, storing energy in the compressed spring. Releasing the spring converts the stored elastic potential energy into kinetic energy.

In both cases, the elastic potential energy comes from the separation of atoms or molecules in the material from their equilibrium spacing. For an ideal spring or other elastic material, the amount of elastic potential energy stored is proportional to the square of the displacement from the equilibrium position. This relationship is described mathematically by Hooke’s law.

## Nuclear Potential Energy

Nuclear potential energy is the potential energy stored within an atom’s nucleus. It is the energy that holds the nucleus together. There are two main types of nuclear potential energy:

### Nuclear Fission

Nuclear fission is the splitting of a large atomic nucleus into smaller nuclei. This process releases enormous amounts of energy, as the potential energy stored in the parent nucleus is converted into kinetic energy. Nuclear fission occurs in power plants, where uranium or plutonium atoms are split to generate electricity.

### Nuclear Fusion

Nuclear fusion is the combining of two light atomic nuclei into a heavier single nucleus. This releases energy, as the fused nucleus has less mass than the original two nuclei. The sun produces energy through nuclear fusion of hydrogen atoms into helium. Fusion is also the process harnessed by hydrogen bombs and experimental fusion reactors.

Both fission and fusion convert nuclear potential energy into heat and radiation through Einstein’s equation E=mc^2. This enormous potential energy comes from the strong nuclear force holding protons and neutrons together within an atomic nucleus.

## Electric Potential Energy

Electric potential energy is the energy stored in an electric field or system of charges. It arises from the electrostatic forces of attraction or repulsion between charged particles such as electrons or protons. Just like gravitational potential energy comes from height, electric potential energy comes from electric potential or voltage.

Some common examples of electric potential energy in action include:

• Capacitors – These devices store electric charge, creating an electric field and voltage. The higher the voltage, the more potential energy is stored in the capacitor.
• Lightning – When storm clouds become charged due to friction between updrafts and downdrafts, huge amounts of electric potential build up. This is discharged in the form of lightning, one of the most dramatic displays of electric potential energy.
• Static Electricity – When materials like wool or rubber are rubbed together, they can transfer electric charge, creating a voltage difference. This can result in static shocks or sparks, releasing the stored potential energy.

Electric potential energy has many practical uses, from jump starting a car battery to powering a defibrillator. It is an essential source of energy for many electrical devices and applications.

## Magnetic Potential Energy

Magnetic potential energy is the potential energy stored in a magnetic field. It refers to the work required to establish a magnetic field, or the energy that can be released when a magnetic field changes. Magnetic potential energy exists whenever magnetic poles or charged particles interact and exert forces on each other.

Some examples of magnetic potential energy in action include:

• The energy stored in an electromagnet when electric current runs through its coil of wire and creates a magnetic field.
• The orientation energy of magnetic materials like iron filings in response to external magnetic fields.
• The interaction energy between planets or stars that have strong magnetic fields.

Magnetic potential energy can be calculated by integrating the magnetic force between two magnets over the distance as they are separated. The potential energy increases as the magnets are moved apart due to the increasing work required against the magnetic force.

## Converting Potential to Kinetic Energy

Potential energy and kinetic energy are closely related. Kinetic energy is the energy of motion – it refers to the movement of an object or particle. Potential energy is stored energy based on an object’s position or arrangement. The law of conservation of energy states that energy cannot be created or destroyed – it can only be converted from one form into another.

There are many examples of the conversion between potential and kinetic energy in everyday life:

• When you lift an object upwards, you are giving it gravitational potential energy. If you then drop the object, this potential energy will convert into kinetic energy as the object accelerates under gravity.
• When a bow is drawn, elastic potential energy is stored in the bent limbs of the bow. When released, this potential energy converts into kinetic energy as the arrow is launched forward.
• In a hydroelectric dam, the water held behind the dam has gravitational potential energy. When the water is released and flows through the turbines, this potential energy gets converted into kinetic energy to generate electricity.
• Chemical potential energy stored in fuels and food can convert into kinetic energy through combustion and metabolic processes.

The conversion between forms of potential energy and kinetic energy allows useful work to be performed. Understanding these energy transformations is key to fields like engineering and physics.

## Potential Energy Applications

Potential energy has many useful applications in technology and inventions that utilize its ability to be converted into kinetic energy. Here are some examples:

Dams and hydroelectric power – The potential energy of water held behind a dam is converted to electricity as the water flows through turbines. This is a major source of renewable energy around the world.

Pumped hydroelectric storage – Water can be pumped uphill into reservoirs when electricity demand is low to store potential energy, then released to generate electricity when demand is high.

Batteries and fuel cells – The chemical potential energy stored in batteries and fuel cells is converted to electrical energy to power devices.

Springs – The potential energy stored in compressed or stretched springs is used in everything from watches to vehicles suspensions to absorb shocks and impacts.

Bow and crossbows – The potential energy from drawing back the bowstring is converted to kinetic energy to propel the arrow or bolt.

Flywheels – Rotating flywheels store kinetic energy as potential energy that can be tapped and released as needed.

Gravity energy storage – Weights are lifted against gravity to store potential energy that can later drive turbines when released.

## Conclusion

Potential energy is a crucial concept in physics and understanding the world around us. This article summarized the main types of potential energy, including gravitational, chemical, elastic, nuclear, electric, and magnetic. We explored how potential energy is stored in a system and can be converted into kinetic energy when released.

Gaining a strong grasp of potential energy enables predicting and calculating the forces, motion, and energy transformations that occur every day. Potential energy powers everything from chemical reactions to nuclear fission and renewable energy generation. Appreciating how potential energy works in simple systems like springs, pendulums, and raised objects provides the foundation for more complex applications.

In summary, the two key components that make up potential energy are a force exerted on an object and the object’s position or configuration. The combination of force and position is what gives an object or system potential energy. This stored energy is waiting to be released in the form of kinetic energy. Developing an intuitive understanding of potential energy is crucial for success in STEM fields and making sense of the physical world.