Science Unit 4 Study Guide

Science Unit 4 Study Guide

Study Guide Outline 

1. Period, frequency, amplitude, wavelength, wave speed (definitions and calculations) 

2. Factors that affect the period of a pendulum 

3. Waves - transverse and longitudinal (diagram), what all waves carry 

4. Parts of a transverse wave - amplitude, wavelength, crest, trough 

5. Parts of a longitudinal wave - wavelength, compression, rarefaction 

6. Sound wave (explain) 

• Volume is related to amplitude 

• Pitch is related to frequency (and inversely related to wavelength) 

• Speed - same for all sound waves in a given medium 

Formulas - know what the letters stand for, their units of measurement, and be able to perform calculations. 𝒗=𝝀·𝒇, 𝒗=𝒅/𝒕, and 𝒇=𝟏/𝑻 

Look at: Binder WS: 4.1, 4.3, 4.5, 4.6, Labs: 10 and 11, and review the OneNote and videos 

Key Vocabulary and Concepts 

1. Frequency (f): 

• Definition: The number of complete wave cycles (oscillations) that pass a fixed point in a unit of time. 

• Unit: Hertz (Hz) 1Hz = 1 cycle per second 

• Symbol: f 

• Explanation: A higher frequency means more waves pass a point in a given time, often corresponding to a higher-pitched sound (for sound waves). 

• Formula: f = 1/T and f = v/λ 

2. Wavelength (λ) 

• Definition: The distance between two consecutive points that are in phase on a wave (e.g., crest to crest or trough to trough). 

• Unit: Meters (m) or centimeters (cm) 

• Symbol: λ "lambda" 

• Explanation: Longer wavelengths correspond to lower frequencies and vice versa, assuming wave speed is constant. 

• Formula: λ = vf 

3. Period (T): 

• Definition: The time taken for one complete wave cycle to pass a given point. 

• Unit: Seconds (s) 

• Symbol: T. 

• Explanation: The period is the reciprocal of frequency, representing the time for one oscillation. 

• Formula: T=1/f 

4. Wave Speed (v): 

• Definition: The rate at which a wave travels through the medium. 

• Unit: Meters per second (m/s) or centimeters per second (cm/s) 

• Symbol: v 

• Explanation: The speed of a wave depends on the medium through which it travels. For example, sound travels faster in solids than in gases. 

• Formula: v=fλ 

5. Amplitude (A): 

• Definition: The maximum displacement of points on a wave from their rest position (equilibrium). 

• Unit: Meters, or any unit of the quantity being displaced (e.g., pressure for sound waves). 

• Symbol: A 

• Explanation: The amplitude determines the energy of the wave. Larger amplitudes correspond to louder sounds or brighter light (for mechanical and electromagnetic waves, respectively). 

Key Relationships 

• Wave Speed Formula:
  v=fλ  This equation links the frequency, wavelength, and speed of a wave. 

• Frequency and Period Relationship:
  f=1/T and T=1/f 

All waves transfer energy

The matter that waves travel through is called a medium.

Period: 

Periodic motion is called "periodic" because it repeats itself at regular intervals of time. The term comes from the word "period," which refers to the time it takes for one complete cycle of the motion to occur. For example: 

• In a pendulum, the motion repeats as it swings back and forth. 

• Ocean waves are characterized by a repeating pattern of crests (highest points) and troughs (lowest points). This repetition occurs at regular time intervals. 

• In planetary orbits, the motion repeats as a planet completes one full revolution around the Sun. 

Since these motions follow a regular and predictable pattern over a defined time interval (the period), they are classified as periodic motions. 

Period refers to the time taken to complete one full cycle of a repeating event, while frequency is the number of cycles that occur within a given unit of time, essentially the inverse of period; meaning, a higher frequency indicates shorter periods between cycles.  

Key points about period and frequency: 

• Period: 

  • Measured in seconds (s) or (s/cycle). 

  • Represents the time taken for one complete oscillation or vibration. 

• Frequency: 

  • Measured in Hertz (Hz) or (cycles/s). 

  • Represents the number of cycles completed per second. 
     

Relationship: 

• Formula: Frequency = 1 / Period 

• Example: If a pendulum swings back and forth once every 2 seconds, its period is 2 seconds, and its frequency would be 0.5 Hz (1 cycle every 2 seconds) 

Frequency (f): 

Definition: The number of complete wave cycles (oscillations) that pass a fixed point in a unit of time.

Unit: Hertz (Hz) 1Hz=1 cycle per second 

What Is Sound? 

Sound is a type of energy created by vibrations. When an object vibrates, it causes the particles in the surrounding medium (such as air, water, or a solid) to vibrate as well. These vibrations create waves of alternating high and low pressure, known as sound waves, which move through the medium. 

How Sound Travels 

Sound travels as a longitudinal wave, where the particles in the medium vibrate back and forth in the same direction as the wave travels. The wave consists of two main parts: 

1. Compression: Areas where particles are pushed together, creating high pressure. 

2. Rarefaction: Areas where particles are spread apart, creating low pressure. 

Sound cannot travel through a vacuum (such as outer space) because there are no particles to carry the vibrations. 

Characteristics of Sound 

Sound can be described using two perspectives: how we perceive it and how scientists measure it. 

1. Perceived Characteristics: 

   • Loudness: How "loud" or "soft" a sound seems to us. 

   • Pitch: How "high" or "low" a sound seems. 

2. Physical Characteristics: 

   • Amplitude: The height of the sound wave. Greater amplitude means louder sound, and smaller amplitude means softer sound. 

   • Frequency: The number of wave cycles per second, measured in hertz (Hz). Higher frequency corresponds to a higher pitch, while lower frequency corresponds to a lower pitch. 

The Relationship Between Frequency, Wavelength, and Speed 

The frequency and wavelength of a sound wave are inversely related: 

• Frequency (f): The number of wave cycles per second. 

• Wavelength (λ): The distance between consecutive compressions or rarefactions. 

The speed of sound (v) depends on the medium through which it travels. It is calculated using the equation: 𝒗=𝒇∙𝝀  

Where: 

• v: Speed of sound (m/s) 

• f: Frequency (Hz) 

• λ: Wavelength (m) 

Sound in Different Mediums 

Sound travels at different speeds depending on the medium: 

• Fastest in solids: Particles are closely packed, allowing vibrations to transfer quickly. 

• Slower in liquids: Particles are less tightly packed than in solids. 

• Slowest in gases: Particles are far apart, making energy transfer slower. 

For example, the speed of sound is approximately 343 m/s in air, but it can reach over 5,000 m/s in steel. 

Applications of Sound 

Sound plays a vital role in communication, music, technology, and science.  

For instance: 

• Ultrasound uses high-frequency sound waves for medical imaging. 

• Echolocation is used by bats and dolphins to navigate and hunt. 

• Acoustic engineering involves designing spaces for optimal sound quality