1. What Is Potential Energy?
Potential energy is the stored energy an object has because of its position or state. It is energy that has the potential to do work in the future.
A lifted object, a stretched rubber band, and water stored in a dam all have potential energy.
1.1. Why It Is Called “Stored” Energy
Even when nothing is moving, energy can be present. This stored energy can be released later to do work — like a stretched bow releasing an arrow.
1.2. Types of Potential Energy
- Gravitational potential energy — due to height.
- Elastic potential energy — due to stretching or compression.
2. Gravitational Potential Energy
This is the energy stored in an object because of its height above the ground. The higher the object is, the more potential energy it has.
2.1. Formula for Gravitational Potential Energy
\( PE = mgh \)
where:
- \( m \) = mass (kg)
- \( g \) = acceleration due to gravity (9.8 m/s² or approx 10 m/s²)
- \( h \) = height above ground (m)
2.2. Understanding the Formula
Gravitational potential energy increases when:
- mass increases
- height increases
- gravity increases
This is why lifting heavy objects requires more effort.
2.3. Real-Life Examples
- Water stored at a height in dams.
- A book kept on a high shelf.
- A child at the top of a slide.
3. Elastic Potential Energy
Elastic potential energy is stored when an object is stretched or compressed. Examples include springs, rubber bands, bows, and trampoline surfaces.
3.1. How It Works
When you stretch a rubber band or compress a spring, you do work on it. This work gets stored as potential energy and can be released later.
3.2. Formula for Elastic Potential Energy (Spring)
For a spring that follows Hooke’s Law:
\( PE = \dfrac{1}{2}kx^2 \)
where:
- \( k \) = spring constant
- \( x \) = extension or compression
3.3. Real-Life Examples
- A pressed spring in a toy car.
- A pulled bow storing energy before releasing an arrow.
- A diving board bending before a diver jumps.
4. Comparing Kinetic and Potential Energy
Kinetic energy is energy of motion, while potential energy is stored energy. An object can switch between these two forms.
4.1. Examples of Energy Conversion
- A falling object: potential energy changes into kinetic energy.
- A roller coaster: high potential energy at the top, high kinetic energy at the bottom.
- A stretched bow: elastic potential energy becomes kinetic energy of the arrow.
5. Units of Potential Energy
The SI unit of potential energy is the Joule (J), the same as work and kinetic energy.
5.1. Everyday Example
When you lift a 1 kg book by 1 metre, the potential energy gained is about 10 Joules.