Chapter 4. Work and Energy
Recommended Article : 【Physics】 Physics Table of Contents
2. Energy
4. Potential Energy due to Gravity
5. Potential Energy due to Elasticity
6. Potential Energy due to Universal Gravitation
7. Power
1. Definition of Work
⑴ Work : Magnitude of applied force × Distance moved in the direction of applied force
⑵ Unit : N·m = kg·m2 / s2 = J
2. Energy
⑴ The ability to do work
⑵ Mechanical energy (E) = Potential energy (EP) + Kinetic energy (EK)
⑶ Law of Conservation of Mechanical Energy : If only conservative forces (e.g., friction, air resistance) act and non-conservative forces are absent, mechanical energy remains constant between initial and final states
⑷ Law of Conservation of Energy
① Through the equivalence of heat and work, it is shown that thermal energy is not significantly different from mechanical energy
② Bernoulli’s principle
○ Content : For every symmetry in nature, there is a corresponding conservation law
○ The universe has symmetry with respect to time
○ The corresponding conservation quantity is considered to be energy
3. Kinetic Energy
⑴ From the kinematic equation 2as = v2 - v02, if we multiply by mass (m), we get mas = 0.5mv2 - 0.5mv02
⑵ Therefore, as F = ma, the change in work is 0.5 mv2 - 0.5mv02, so if v0 = 0, kinetic energy is 0.5 mv2
4. Potential Energy due to Gravity
⑴ The magnitude of gravity is mg, and the displacement is h, so the potential energy due to gravity during displacement is mgh
⑵ Potential energy is a relative value and can vary depending on the reference point even at the same position
5. Potential Energy due to Elasticity
⑴ Elastic force is not constant when the length changes; it’s proportional to the change in length, so the average elastic force acting over an elongation of x units from the original position is 0.5 kx
⑵ Therefore, the potential energy due to elastic force at x is 0.5 kx × x = 0.5 kx2
① Integration can be applied
6. Potential Energy due to Universal Gravitation
⑴ Potential energy due to universal gravitation at a position R from the center
7. Power
⑴ Work per unit time P = W/t
⑵ Unit : N·m/s = W
⑶ P = W / t = F · S / t = F · v
Input : 2016.06.26 21:05