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Oscillations and waves (Essentials) - Class 11th

Course: Oscillations and waves (Essentials) - Class 11th > Unit 2

Lesson 3: How does energy change as a particle oscillates?
Science
Oscillations and waves (Essentials) - Class 11th
How does mass of an attached object affect the motion of a spring?
How does energy change as a particle oscillates?
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Energy of simple harmonic oscillator review

Google Classroom
Overview of equations and skills for the energy of simple harmonic oscillators, including how to find the elastic potential energy and kinetic energy over time. Understand how total energy, kinetic energy, and potential energy are all related.

Equations

EquationSymbol breakdownMeaning in words
U, start subscript, s, end subscript, equals, start fraction, 1, divided by, 2, end fraction, k, x, squaredU, start subscript, s, end subscript is the elastic potential energy, k is spring constant, and x is length of extension or compression relative to the un-stretched length.The elastic potential energy is directly proportional to the square of the change in length and the spring constant.
delta, U, start subscript, g, end subscript, equals, m, g, delta, ydelta, U, start subscript, g, end subscript is change in gravitational potential energy, m is mass, g is the gravitational field strength, and delta, y is change in height.The change in gravitational potential energy is directly proportional to mass, gravitational field strength, and change in height.
K, equals, start fraction, 1, divided by, 2, end fraction, m, v, squaredK is translational kinetic energy, m is mass, and v is the speed.Translational kinetic energy is directly proportional to mass and the square of the speed.

How to find energy over time for a simple harmonic oscillator

Elastic potential energy

Elastic potential energy depends upon the position of our system, so a position vs. time graph can be used to find the elastic potential energy U, start subscript, s, end subscript over time for a simple harmonic oscillator. There are a few important points to note when comparing the position and energy graphs:
  • U, start subscript, start text, s, comma, space, m, a, x, end text, end subscript occurs when the system is at the maximum displacement of A and minus, A.
  • U, start subscript, s, end subscript, equals, 0 occurs when the system is at x, equals, 0.

Kinetic energy

Kinetic energy K depends upon the speed of a system, so a velocity vs. time graph can be used to find the kinetic energy over time for simple harmonic oscillator. There are a few important points to notice when comparing the velocity and energy graphs:
  • K, start subscript, start text, m, a, x, end text, end subscript occurs when the system is at its maximum speeds vertical bar, v, start subscript, start text, m, a, x, end text, end subscript, vertical bar and vertical bar, minus, v, start subscript, start text, m, a, x, end text, end subscript, vertical bar.
  • K, equals, 0 occurs when v, equals, 0.
Figure 2. A comparison of the velocity vs. time graph and kinetic energy vs. time graph for a simple harmonic oscillator.

Total energy

The total energy is the sum of the kinetic and elastic potential energy of a simple harmonic oscillator:
E, equals, K, plus, U, start subscript, s, end subscript
The total energy of the oscillator is constant in the absence of friction. When one type of energy decreases, the other increases to maintain the same total energy.
Figure 3. A graph of energy vs. time for a simple harmonic oscillator. This graph shows total energy E, start subscript, start text, t, o, t, end text, end subscript (purple), kinetic energy K (red), and elastic potential energy U, start subscript, s, end subscript (blue).
There are a few important points to keep in mind about energy:
  • U, start subscript, start text, s, comma, space, m, a, x, end text, end subscript occurs when K, equals, 0. This happens at the endpoints of the oscillation where the system momentarily stops (v, equals, 0) at the maximum displacement.
  • K, start subscript, start text, m, a, x, end text, end subscript occurs at U, start subscript, s, end subscript, equals, 0. This is when the system is moving through the equilibrium position (x, equals, 0) and has its maximum speed.
  • E, start subscript, start text, t, o, t, end text, end subscript is constant, so E, start subscript, start text, t, o, t, end text, end subscript, equals, K, start subscript, start text, m, a, x, end text, end subscript, equals, U, start subscript, start text, s, comma, space, m, a, x, end text, end subscript.

Learn more

To check your understanding and work toward mastering these concepts, check out our exercises:

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