⚡️ The principle that the total energy of an isolated system remains constant over time, even though it can change form. Think of it like a closed bank account: you can transfer money between checking and savings, but the total amount stays the same. In physics, energy can shift between kinetic, potential, thermal, chemical, etc., but the sum is unchanged (ignoring external work or heat transfer).
For a closed system: \$E{\text{total}} = K + U + E{\text{other}} = \text{constant}\$
Where \$K\$ = kinetic energy, \$U\$ = potential energy, and \$E_{\text{other}}\$ = any other forms (thermal, chemical, etc.).
When analysing a problem, follow these steps:
Example: A 2 kg block slides down a 5 m frictionless incline. Find its speed at the bottom.
Solution:
Initial: \$Ki = 0\$, \$Ui = mgh = 2 \times 9.8 \times 5 = 98\$ J.
Final: \$Kf = \frac{1}{2}mv^2\$, \$Uf = 0\$.
Conservation: \$98 = \frac{1}{2} \times 2 \times v^2 \Rightarrow v = \sqrt{98} \approx 9.9\$ m s⁻¹.
📚 Remember:
⚠️ Avoid mixing up kinetic and potential energy signs – kinetic is always positive, potential can be negative depending on the chosen reference point.
Which of the following is NOT a form of energy that can be conserved in a closed system?
Answer: None – all can be conserved.