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Chapter 16: Problem 11

A (somewhat risky) way of telling if a train that cannot be seen or heard is approaching is by placing your ear on the rail. Explain why this works.

Short Answer

Expert verified
Answer: Placing your ear on a railway track helps detect an approaching train because sound waves travel faster and more efficiently through the solid steel track than through air, allowing you to sense the vibrations created by the train's movement even if it's too far away to be heard through the air. However, this method is not recommended for safety reasons as it puts individuals at risk of being too close to the tracks when a train approaches.

Step by step solution

01

Understanding sound waves

Sound is a vibrational energy transmitted through mediums like air, water, and solids. The vibration causes the particles in the medium to oscillate back and forth, creating sound waves. These sound waves are longitudinal waves that travel at different speeds depending on the medium.
02

Properties of solids for sound transmission

In solids, particles are more densely packed than in air or water, allowing them to transmit sound waves faster and more efficiently. The speed of sound in steel, which is the primary material used in railway tracks, is around 5,120 meters per second (m/s), while in air, it is approximately 343 m/s. Thus, sound travels significantly faster through steel than through air.
03

Detecting vibrations through the ear

Our ears can detect the vibrations created by sound waves in the environment. When you place your ear on a solid surface, like a railway track, you can effectively detect the vibrations that travel along the track. This means that if a train is approaching, even from a distance, the vibrations from the train's movement will propagate through the steel track and your ear will sense the vibrations more easily when in direct contact with the track.
04

Why it works for detecting approaching trains

Placing your ear on the railway track allows you to effectively detect an approaching train because the solid track can transmit the sound waves faster and more efficiently than through air. As a result, you can sense the vibrations created by the train's movement even if it's too far away to be heard through the air. This helps in determining if a train is coming without actually seeing or hearing it through the air, although it is a risky method and not recommended for safety reasons.

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Most popular questions from this chapter

You are driving along a highway at \(30.0 \mathrm{~m} / \mathrm{s}\) when you hear a siren. You look in the rear-view mirror and see a police car approaching you from behind with a constant speed. The frequency of the siren that you hear is \(1300 \mathrm{~Hz}\). Right after the police car passes you, the frequency of the siren that you hear is \(1280 \mathrm{~Hz}\). a) How fast was the police car moving? b) You are so nervous after the police car passes you that you pull off the road and stop. Then you hear another siren, this time from an ambulance approaching from behind. The frequency of its siren that you hear is \(1400 \mathrm{~Hz}\). Once it passes, the frequency is \(1200 \mathrm{~Hz}\). What is the actual frequency of the ambulance's siren?

A thin aluminum rod of length \(L=2.00 \mathrm{~m}\) is clamped at its center. The speed of sound in aluminum is \(5000 . \mathrm{m} / \mathrm{s}\). Find the lowest resonance frequency for vibrations in this rod.

The Moon has no atmosphere. Is it possible to generate sound waves on the Moon?

A police siren contains at least two frequencies, producing the wavering sound (beats). Explain how the siren sound changes as a police car approaches, passes, and moves away from a pedestrian.

You are creating a sound wave by shaking a paddle in a liquid medium. How can you increase the speed of the resulting sound wave? a) You shake the paddle harder to give the medium more kinetic energy. b) You vibrate the paddle more rapidly to increase the frequency of the wave. c) You create a resonance with a faster-moving wave in air. d) All of these will work. e) None of these will work. f) Only (a) and (b) will work. g) Only (a) and (c) will work. h) Only (b) and (c) will work.
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