Objective:
Recall and use the equation for the change in gravitational potential energy: \$\Delta E_p = m g \Delta h\$
Think of a ball held at the top of a hill. The higher it is, the more “energy” it has stored, ready to be released if it rolls down. This stored energy is called gravitational potential energy (GPE). The amount of GPE depends on three things: the mass of the object, the height above the ground, and the strength of gravity.
| Symbol | Meaning | Units |
|---|---|---|
| \$m\$ | Mass of the object | kg |
| \$g\$ | Acceleration due to gravity (≈9.8 m s⁻² on Earth) | m s⁻² |
| \$\Delta h\$ | Change in height (final height – initial height) | m |
Imagine a water tank at the top of a hill. The higher the tank, the more potential energy the water has. When you open the tap, the water rushes down, turning that potential energy into kinetic energy (motion). The same principle applies to any object lifted against gravity.
\$\Delta E_p = (2.0\;\text{kg})(9.8\;\text{m s}^{-2})(1.5\;\text{m}) = 29.4\;\text{J}\$
So the book now has 29.4 J of gravitational potential energy.