Basics of Simple Harmonic Motion
When an object moves back and forth around a fixed position, it is engaging in Simple Harmonic Motion (SMH). This form of motion is especially prevalent in items that oscillate in a consistent manner such pendulums and springs.
Definition and Characteristics of Simple Harmonic Motion
Simple Harmonic Motion is a form of oscillatory movement that can be described as such:
- The object oscillates about a fixed equilibrium position
- When an object is displaced from equilibrium, a restoring force acts in the direction of the equilibrium position
- As the displacement from equilibrium increases so does the magnitude of the restoring force increases
The repeating, oscillatory motion can be attributed to the restoring force that called the object to move in the opposite direction of its current motion. In an ideal system featuring SMH, this repeating motion occurs perpetually and with no energy loss.
A common example of SMH is a mass attached to a spring. When the spring is displaced, a restoring force acts in the opposite direction, causing the block to oscillate.
Equilibrium and Restoring Behavior
When the net force acting on the object is zero, it is in the equilibrium position. Due to the balanced forces, the object experiences no acceleration at the equilibrium position.
The spring becomes stretched or compressed when displaced from equilibrium, causing a restoring force that acts opposite the direction of displacement. This causes the object to accelerate toward equilibrium due to the introduction of unbalanced forces on the object.
This restoring force ensures that the object does not remain displaced and instead continues to oscillate around the equilibrium position.
Displacement and Oscillatory Motion
Displacement refers to the change in the position of the object relative to its position at the equilibrium point. Depending on the side of the equilibrium point where the object is located, the sign that describes the displacement of an object varies.
One complete cycle of motion is referred to as an oscillation. In SMH, an oscillation typically means that the object moves from an extreme position, through the equilibrium point, and to the opposite extreme position. This pattern is periodic and repeats itself in a consistent manner.
Amplitude
The maximum magnitude of displacement from equilibrium is called in the amplitude. Amplitude is the greatest change in distance from the equilibrium point during an oscillation.
Properties of amplitude:
- Distance from an extreme position to the equilibrium point
- In ideal systems with no energy loss, it remains constant
If an object is displaced farther away from its equilibrium position prior to being released, the magnitude of the object will increase as well.
Period and Frequency
The time (in seconds) needed for an object to complete a full oscillation is called the period of Simple Harmonic Motion. On the other hand, frequency describes the number of oscillations that occur per second (also known as hertz or Hz). A shorter period corresponds to a higher frequency due to the inversely proportional relationship between frequency and period.
In the image above, the spring is initially in its equilibrium position (unstretched) and after being displaced, it moves a maximum distance from the equilibrium position (amplitude) in a consistent period.
Summary
Simple Harmonic Motion (SHM) is a type of motion involving an object that moves back and forth around a fixed position. A restoring force that is pointed toward the equilibrium position of the object is responsible for this motion. Using terms such as displacement, amplitude, period, and frequency, various aspects of oscillation can be described. The concept of SMH is noticeable in various real-life applications such as springs, pendulums, and mechanical oscillators.
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