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## AP®︎/College Physics 1

### Course: AP®︎/College Physics 1>Unit 8

Lesson 1: Introduction to simple harmonic motion

# Definition of amplitude and period

David defines the terms amplitude and period for simple harmonic motion and shows how to find them on a graph. Created by David SantoPietro.

## Want to join the conversation?

• Shouldn't the amplitude get lower and lower with each cycle? If you imagine a spring that has been extended and then let go, it wouldn't come back to the original position after one cycle, rather it would be slightly less displaced. Am I missing something?
• This video is ignoring friction and air resistance.
• I have a confusion between the time period and the wavelength. Could you help me out?
• Think of a water wave traveling on the ocean...

wavelength is a distance between two nearby peaks.

time period is the time it takes the wave to travel a distance of one wavelength
also
if a seagul was bobbing up down as the waves pass, the time period is how long it would take to go down, up and back to its original posiiton
• If there is a spring on the ceiling and I pulled it down and I let go would the amplitude and the period decrease until the spring stops ocillating because of gravity or would they stay constant
• from my point of view the problem is that at the equilibrium position the net forces acting on the body is not zero as there is air lifting force (during motion)
first you pull the weight down so it makes amplitude A1
it rebounds upward to make an amplitude A2
where A2 < A1 because of the body weight and air lifting force
then i think it would make damping oscillation until it stops but i don't know how the acting forces will cause this damping oscillation
• what is the unit of Amplitude ??
• Some measure of displacement. Perhaps cm.
• Is like valley is the amplitude?
• Yes. My mistake. Amplitude is level ground up to hill or level ground to bottom of valley

• what is the value of constant k
• Varies, in this example, from spring to spring. Some can be stiffer than others, meaning that a small displacement of the spring creates a huge force, i.e. the value of k is larger.
• Is it possible that maximum displacement on one side is not equal to max. displacement on the other side? Both are usu. equal to amplitude. But is it even possible, say it is an old worn-out spring? Is it still a wave if it is not?
• Take for example, a spring anchored at x = 0 with a mass at rest at x = x_1. If the mass is then displaced and released at rest at x > 2 * x_1, our simple picture breaks no matter how perfect the spring is. Your answer is that while, yes, the the graph, as described in the video, of position over time will still resemble a wave, it is not precisely a sine wave for extreme values.
(1 vote)
• why distance between crests and troughs are equal?
and why this distance is two times of distance between a crest and trough?
(1 vote)
• The compressive and tensile force of a spring described as a simple harmonic oscillator are equal in magnitude but opposite in direction (F = -kx). Notice that this equation results in an F of equal magnitude if we invert x. As for your second question, wavelength is defined in this way because it is easier think about the wavelength as fundamental to the wave when one wavelength represents all "parts of the wave" exactly one time.
(1 vote)
• If a bob in a pendulum moves in a circular or elliptical path and not in to and fro motion will it be an oscillation.