Unit 4.3 – Potential Energy

1. Gravitational Potential Energy (GPE):
   This is the energy stored in an object due to its height above the ground. The higher the object, the more gravitational potential energy it has.
2. Elastic Potential Energy:
   This is the energy stored in elastic materials like springs or rubber bands when they are stretched or compressed.

• $𝑚$ = Mass of the object (in kilograms, kg)
• $𝑔$ = Acceleration due to gravity ($9.8𝑚\mathrm{/}{𝑠}^2$)
• $ℎ$ = Height of the object above the ground (in meters, m)

1. Dependence on Height:
   The higher an object is placed, the more gravitational potential energy it has. For example, a book on a high shelf has more GPE than the same book on a lower shelf.
2. Dependence on Mass:
   Heavier objects have more potential energy than lighter ones at the same height. For example, a brick on a table has more GPE than a feather at the same height.
3. Units of Potential Energy:
   The SI unit of potential energy is Joule (J), just like work and kinetic energy.

1. Water stored in a dam has gravitational potential energy, which can be converted into electricity when released.
2. A compressed spring in a toy car stores elastic potential energy, which propels the car forward when released.

Quick Review, Exam Tips, Tricks & Traps

1. Potential energy depends on mass, height, and gravity for gravitational potential energy.
2. Elastic potential energy depends on how much a material is stretched or compressed.
3. Potential energy is always relative to a reference point (e.g., ground level for GPE).

1. Always use the correct value of $𝑔=9.8𝑚\mathrm{/}{𝑠}^2$ unless the question specifies otherwise.
2. Check whether the height ($ℎ$) is measured from the correct reference point. Misinterpreting the reference can lead to wrong answers.

1. Students often forget that potential energy depends on height. For example, an object on the ground ($ℎ=0$) has zero gravitational potential energy.
2. Confusion between gravitational and elastic potential energy. Always identify the type of potential energy being discussed in the question.

1. Use proportional reasoning:
   • If height doubles, $𝐺𝑃𝐸$ doubles.
   • If mass doubles, $𝐺𝑃𝐸$ also doubles.
2. In MCQs, eliminate options where potential energy decreases with increasing height—it’s impossible unless the object moves below the reference point.