Physics Revision: Sound and Motion

Comprehensive question-and-answer revision flashcards covering sound waves, hearing mechanisms, oscilloscope traces, motion equations, measurement precision, and motion graphs.

How does a vibrating object produce sound and transfer energy through a medium?

A vibrating object causes nearby particles to vibrate back and forth about fixed positions. These particles transfer energy through the medium without traveling with the wave itself.

Why is sound unable to travel through a vacuum?

Sound cannot travel through a vacuum because there are no particles present to carry the vibrations.

Why is sound classified as a longitudinal wave in air?

Because air particles vibrate parallel to the direction of wave travel.

In the diagram of a sound wave shown below, what do regions X, Y, and Z represent?

$X$ and $Z$ represent compressions (regions of higher pressure where particles are closer together), and $Y$ represents a rarefaction (a region of lower pressure where particles are farther apart).

How is wavelength defined for a longitudinal sound wave?

Wavelength is the distance from one compression to the next, or from one rarefaction to the next (measured in metres, $\text{m}$).

What are the approximate speeds of sound in air, water, and steel?

In air: approximately $340\,\text{m/s}$; in water: approximately $1500\,\text{m/s}$; in steel: approximately $5000\,\text{m/s}$.

Why does sound generally travel fastest in solids and slowest in gases?

In solids, strong interactions between closely spaced particles allow vibrations to transfer rapidly. In gases, particles are farther apart.

What is the sequence of structures in the human hearing pathway?

Pinna collects sound $\rightarrow$ ear canal carries sound $\rightarrow$ eardrum vibrates $\rightarrow$ ossicles transmit vibrations $\rightarrow$ fluid and sensory hair cells in the cochlea respond $\rightarrow$ electrical impulses travel along the auditory nerve $\rightarrow$ brain interprets sound.

Which specific anatomical structures comprise the outer ear, middle ear, and inner ear?

Outer ear: pinna and ear canal. Middle ear: ossicles (hammer, anvil, and stirrup). Inner ear: cochlea. (The eardrum separates the outer and middle ear.)

How do microphones and speakers convert signals?

A microphone converts sound into an electrical signal (sound vibrates a diaphragm, moving a coil near a magnet). A speaker converts an electrical signal into sound (a coil moves a cone, vibrating the air).

How do the perceived properties of loudness and pitch relate to wave quantities?

Loudness relates to amplitude (greater amplitude results in a louder sound). Pitch relates to frequency (greater frequency results in a higher pitch).

Based on the oscilloscope traces shown below, what wave characteristics distinguish a loud sound from a high-pitched sound?

Loudness is determined by amplitude (the vertical height from the centre line to a peak), while pitch is determined by frequency (the number of complete wave cycles occurring in the same amount of time).

On an oscilloscope screen displaying a sound signal, what does one horizontal cycle represent?

One horizontal cycle represents the period ($T$), not the wavelength.

How is frequency calculated from period, and what is the frequency of $80$ vibrations occurring in $0.20\,\text{s}$?

$\text{Frequency} = \frac{1}{\text{period}}$. For $80$ vibrations in $0.20\,\text{s}$, the frequency is $\frac{80}{0.20} = 400\,\text{Hz}$ (with each vibration having a period of $0.0025\,\text{s}$).

What is the typical audible hearing range for a healthy young person, and what is ultrasound?

Healthy human hearing ranges from about $20\,\text{Hz}$ to $20\,000\,\text{Hz}$. Ultrasound is defined as sound with a frequency above $20\,000\,\text{Hz}$.

What are three common applications of ultrasound?

Medical imaging, finding cracks in materials, and depth measurement using reflected pulses.

What are the typical decibel ($\text{dB}$) levels for a whisper, conversation, and loud machinery, and what factors determine hearing damage?

Whisper: about $20\,\text{dB}$; conversation: about $60\,\text{dB}$; loud machinery or concerts: can exceed $100\,\text{dB}$. Hearing damage depends on sound level and exposure time.

What is the formula used to calculate average speed?

$$\text{Average speed} = \frac{\text{total distance}}{\text{total time}}$$

How do you convert speed between $\text{km/h}$ and $\text{m/s}$?

To convert from $\text{km/h}$ to $\text{m/s}$, divide by $3.6$ (e.g., $50\,\text{km/h} \div 3.6 = 13.9\,\text{m/s}$). To convert from $\text{m/s}$ to $\text{km/h}$, multiply by $3.6$.

What is the difference between accuracy and precision in scientific measurements?

Accuracy means a result is close to the true value. Precision means repeated results are consistent and repeatable.

Why are light gates and electronic timers preferred over hand-held stopwatches for timing short events?

Human reaction time is about $0.2\,\text{s}$, introducing error into hand-held timing. Light gates and electronic timers start and stop automatically, reducing reaction-time error.

What is the definition and formula for acceleration?

Acceleration is the change in speed per unit time. The formula is: $\text{acceleration} = \frac{\text{final speed} - \text{initial speed}}{\text{time}}$, with the unit $\text{m/s}^2$.

What does a negative acceleration value indicate?

A negative value indicates deceleration (slowing down), where the final speed is lower than the initial speed.

What does a horizontal line indicate on a distance-time graph versus a speed-time graph?

On a distance-time graph, a horizontal line means the object is stationary. On a speed-time graph, a horizontal line means the object is moving at a constant speed.

What does an upward straight line represent on a distance-time graph versus a speed-time graph?

On a distance-time graph, an upward straight line represents constant speed. On a speed-time graph, an upward straight line represents constant acceleration.

What does a downward-sloping line indicate on a distance-time graph compared to a speed-time graph?

On a distance-time graph, a downward line means returning towards the starting point (if the axis represents distance from a fixed point). On a speed-time graph, a downward line means speed is decreasing (deceleration).

What happens to a falling object at terminal velocity, and how is this depicted on a speed-time graph?

A falling object initially accelerates until upward air resistance balances its downward weight, causing speed to become constant. On a speed-time graph, this is shown by a horizontal line.