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A rectangle has the dimensions of \(3.0 \mathrm{m} \times 2.0 \mathrm{m}\) when viewed by someone at rest with respect to it. When you move past the rectangle along one of its sides, the rectangle looks like a square. What dimensions do you observe when you move at the same speed along the adjacent side of the rectangle?

Short Answer

Expert verified
Both lengths observed are 2.0 m.

Step by step solution

01

Understanding the Problem

The problem involves a rectangle and involves moving past it at a high speed, which causes relativistic effects. Initially, the rectangle has a length of 3.0 m and a width of 2.0 m. When observed by someone moving along a side at high speed, it appears as a square.
02

Applying Length Contraction

Since the rectangle appears as a square, the length of the rectangle along the direction of motion is contracted due to relativistic effects. The person sees equal dimensions, thus the contracted dimension must equal the other unaffected side, i.e., 2.0 m. Therefore, using length contraction:\[ L = L_0 imes rac{1}{ ext{Lorentz factor}} \]Without the exact speed, specific calculations aren't required, but given it appears square, the contracted side must be 2.0 m.
03

Observing from Along the Width

When you move at the same speed along the adjacent side (the side that was not contracted initially), the contraction affects this new direction. Originally this side is 2.0 m, which now appears as:\[ 2.0 ext{ m contracted to a new value while height remains 3.0 m} \]Since the observation from the previous motion showed as a square, the observed dimension must be 2.0 m.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Lorentz Factor
The Lorentz Factor is a crucial concept in understanding the effects of relativity on objects moving at high velocities. It is denoted by the symbol \( \gamma \) and is calculated using the equation: \[ \gamma = \frac{1}{\sqrt{1 - \frac{v^2}{c^2}}} \] where \( v \) represents the velocity of the object and \( c \) is the speed of light in a vacuum.
The Lorentz Factor becomes significant when the velocity \( v \) approaches the speed of light. At these high speeds, relativistic effects such as time dilation and length contraction become noticeable.
  • Time Dilation: Time appears to move slower for objects in motion relative to a stationary observer.
  • Length Contraction: Objects appear shorter in the direction of motion from the perspective of a stationary observer.
In the rectangle problem, the Lorentz Factor helps explain why one side of the rectangle appears contracted when viewed by someone moving along one of its sides.
Relativity
Relativity, specifically Einstein's theory of relativity, revolutionized our understanding of how objects behave at high speeds. This theory has two main components: special relativity and general relativity.
  • Special Relativity: Focuses on objects moving at constant speeds, particularly at speeds close to the speed of light. It deals with concepts such as time dilation and length contraction.
  • General Relativity: Focuses on gravity and the effect of massive objects on the curvature of spacetime.
In the context of the rectangle exercise, special relativity is at play. As you move at high speeds relative to the rectangle, length contraction occurs, making the rectangle appear as a square. This phenomenon is a fundamental aspect of how motion influences perception of length in relativistic physics.
Geometry in Physics
Geometry in physics often goes beyond the static geometries we learn in traditional math. When considering relativistic scenarios, geometry becomes dynamic and dependent on the observer's frame of reference.
In this case, the rectangle initially measures as a 3.0 m by 2.0 m shape when at rest. However, upon observing it while moving at high velocities, the rectangle's geometry appears distorted due to length contraction. Specifically:
  • The side in the direction of motion contracts, causing it to appear shorter.
  • The unaffected side remains the same length, leading the overall shape to become a square from that moving perspective.
This illustrates how geometry in physics can change with the speed and orientation relative to an observer, highlighting the unique interplay between motion and physical dimensions within relativistic frameworks.

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Most popular questions from this chapter

Suppose that you are planning a trip in which a spacecraft is to travel at a constant velocity for exactly six months, as measured by a clock on board the spacecraft, and then return home at the same speed. Upon your return, the people on earth will have advanced exactly one hundred years into the future. According to special relativity, how fast must you travel? Express your answer to five significant figures as a multiple of \(c-\) for example, \(0.95585 \mathrm{c}\)

What is the magnitude of the relativistic momentum of a proton with a relativistic total energy of \(2.7 \times 10^{-10} \mathrm{J} ?\)

An electron and a positron have masses of \(9.11 \times 10^{-31} \mathrm{kg} .\) They collide and both vanish, with only electromagnetic radiation appearing after the collision. If each particle is moving at a speed of \(0.20 \mathrm{c}\) relative to the laboratory before the collision, determine the energy of the electromagnetic radiation.

Three particles are listed in the table. The mass and speed of each particle are given as multiples of the variables \(m\) and \(v\), which have the values \(m=1.20 \times 10^{-8} \mathrm{kg}\) and \(v=0.200 \mathrm{c} .\) The speed of light in a vacuum is \(c=3.00 \times 10^{8} \mathrm{m} / \mathrm{s}\). Determine the momentum for each particle according to special relativity. $$ \begin{array}{clc} \hline \text { Particle } & \text { Mass } & \text { Speed } \\ \hline \mathrm{a} & m & v \\ \mathrm{b} & \frac{1}{2} m & 2 v \\ \mathrm{c} & \frac{1}{4} m & 4 v \\ \hline \end{array} $$

You are driving down a two-lane country road, and a truck in the opposite lane is traveling toward you. Suppose that the speed of light in a vacuum is \(c=65 \mathrm{m} / \mathrm{s}\). Determine the speed of the truck relative to you when (a) your speed is \(25 \mathrm{m} / \mathrm{s}\) and the truck's speed is \(35 \mathrm{m} / \mathrm{s}\) and (b) your speed is \(5.0 \mathrm{m} / \mathrm{s}\) and the truck's speed is \(55 \mathrm{m} / \mathrm{s}\). The speeds given in parts (a) and (b) are relative to the ground.

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