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# Oscillations - The beginning to studying waves

Updated: Feb 21

I can’t be the only one who thought I knew exactly what waves was before starting learning about them. I mean,

every three year old who’s seen water knows what they look like, and that they are fun to sail upon. I couldn’t have been more wrong.

Granted, I realized this in 7th grade when we had a short summary about waves in school, but by the end of that topic, I sighed and thought “Well, now I know all about waves” Then the IB topics on waves started.

In the IB syllabus, waves are one or two topics depending on level (1 for standard level and 2 for higher). The first topic (topic 4) is the basics of waves and about understanding them, while the second topic (topic 9) contains more equations and calculations. If you are like me, and thinks using values and placing them into equations is far easier than actually understanding them, you’ll find topic 9 to be easier than topic 4. But, since I’m here to describe in simple words what the syllabus contains, I guess I’ll start with 4.1 - Oscillations.

The first thing we should define is what an oscillation is. According to Cambridge Dictionary (1), the physics definition is “to change regularly in strength or direction ”. Examples of these include a heart beating, tides on the oceans, and of course waves of various kinds that are transmitted by oscillations.(2) If the time taken for each oscillation is the same, it’s called simple harmonic oscillation, or simple harmonic motion. To observe them, the school often makes use of a pendulum or a mass on a spring.

Simple harmonic motion (SHM) = Periodic motion where the restoring force is proportional to the displacement in the opposite direction.

This can also be described as F ∝ − x Remember the negative sign, as it indicated that the force is in the opposite direction to the displacement, hence acts opposite to the motion and restores the object in question.(3)

However, this is not the actual definition of SHM. Instead, simple harmonic motion is defined as an oscillation is defined as an oscillation where the acceleration, a, of a body is proportional to its displacement in the opposite direction. Thinking about it a little, it makes sense, because we know Newton’s 2nd law describes acceleration as proportional to force. Therefore, if something is proportional to force, it is also proportional to acceleration.

Simple harmonic motion (SHM) : Periodic motion where the acceleration of a body is proportional to the displacement in the opposite direction.

That’s all for now! In the next post, I hope to show graphs of simple harmonic motion and describe how energy changes during the oscillations. Until then, you could practice on these concepts that are described below, because that is so much fun... and you’ll need them, because the IB syllabus says so 😉

Equilibrium position : The place where the object would stay with no resultant force Displacement, x : The distance in a given direction from the equilibrium position

Time period, T : The time it takes to complete one oscillation (to return to the same position, moving in the same direction)

Frequency, f : Number of oscillations in a unit time (usually per second). The relationship between frequency and time period is T = 1f . You’ll find this equation in

the data booklet.

Amplitude, A : The maximum displacement (from equilibrium position)

Phase difference: Used to describe the difference between two or more oscillations. While it is possible that they have different frequency, it is more often used as a measure of oscillations of the same frequency.

If two oscillations pass through the equilibrium position at the exact same time, they are described to be in phase, if they are not they have a phase difference.

If one oscillation is always half an oscillation apart from the other, the two are exactly out of phase.

Sources:

(1) https://dictionary.cambridge.org/ (2) Allum, John and Talbot, Christopher. Physics for the IB Diploma . 2nd edn . London: Hodder Education, 2014, 141 (3) ibid, 145

Allum, John and Talbot, Christopher. Physics for the IB Diploma . 2nd edn . London: Hodder Education, 2014 https://dictionary.cambridge.org/ (2018-02-10)

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