Energy in Oscillations (Oxford AQA IGCSE Physics)
Revision Note
Written by: Leander Oates
Reviewed by: Caroline Carroll
Energy in Oscillations
An oscillating object moves back and forth in a regular rhythm
The energy in an oscillating system is transferred back and forth between gravitational potential and kinetic energy stores
Examples of oscillating objects are:
A simple pendulum
A guitar string
A swing
A bungee jump
A mass on a spring
Alternating current
A simple pendulum consists of a mass (called a bob) on a string
If the bob is displaced from its equilibrium position and left to swing freely, it will oscillate
A simple pendulum
As the pendulum oscillates, energy is transferred back and forth between the gravitational potential and kinetic stores
In an ideal system (where there is no air resistance) the total energy of the oscillating pendulum remains constant
The position at which the pendulum would hang undisturbed is called the equilibrium position
The pendulum is considered to have zero gravitational potential energy at the equilibrium position
As the pendulum is displaced from the equilibrium position, energy is transferred to its gravitational potential store
When the pendulum is released and begins to swing, energy is transferred from the gravitational potential store to the kinetic store
The pendulum has the most kinetic energy as it swings through the equilibrium position because this is when its velocity is the greatest
As it swings past the equilibrium position to the other side of the oscillation, energy is transferred from the kinetic store to the gravitational potential store
As the pendulum bob reaches its point of maximum displacement from the equilibrium position, its velocity slows to zero (at the point at which it changes direction) so there is zero energy in its kinetic store and maximum energy in its gravitational potential store
Energy changes in an oscillating object
Worked Example
At a certain point in the oscillation of a simple pendulum, the ideal system has 8 J in the kinetic store and 13 J in the gravitational potential store.
Determine the total energy in the oscillating system.
Answer:
Step 1: List the known quantities
Kinetic energy,
Gravitational potential energy,
Step 2: Recall the relationship between total energy, kinetic energy, and gravitational potential energy
The total energy of the system remains constant
Energy is transferred back and forth between the kinetic and gravitational potential stores
Therefore:
Step 3: Determine the total energy of the system
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