In this topic we look at:
- oscillations of bodies that move back and forth periodically
- progressive waves that transfer energy and information through space
- the interference effects of these progressive waves, and other phenomena
- standing waves, where waves combine to become stationary (and therefore transferring no energy at all)
You will learn about simple harmonic motion, dispersion and guitar string frequencies, and be able to answer the following questions:
- How does a force that is proportional to displacement result in an oscillation?
- Are all oscillations simple harmonic?
- What is the connection between oscillations and waves?
- Are waves really made of an infinite number of wavelets?
We represent a sound wave by drawing lines like the coils of a slink spring but we should remember that although layers of air oscillate the individual atoms do not.
It is not at all obvious that a sinusoidally varying displacement is a consequence of the condition that the acceleration is proportional to displacement but in the opposite direction, that is until you differentiate the sin function in maths of course.
To understand the propagation of electromagnetic waves you need to have studied the next section on electromagnetism. However it is enough to use what we know about other waves to understand the wave nature of light.
Another physics book classic, the mass hanging on a spring. A bit easier to analyse than a pendulum but not as easy as the mass on a spring in space. Quite obvious that the acceleration is proportional to displacement, once you realise that SHM follows.
A juggler may not understand the mathematical representation of phase but the are using the effect as they throw balls in the air at different times. It is important to understand the concept of phase before starting the waves section.
It is easy to observe the wave motion in a string but it doesn´t tell the whole story of wave properties. A string wave can't diffract or interfere. Sometimes simple explanations cause misunderstandings. Here a string wave is polarised by a narrow slit.