Space Contraction: Shortening Distance for Fast Moving Objects

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  • 0:06 Space and Size
  • 1:15 Length Contraction
  • 2:57 Length Contraction and…
  • 4:28 What Is Speed?
  • 5:51 Lesson Summary
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Lesson Transcript
Instructor: John Simmons

John has taught college science courses face-to-face and online since 1994 and has a doctorate in physiology.

The length of a moving object decreases in the same direction it travels. This phenomenon is referred to as space or length contraction. Scientists have proven that space contraction occurs and becomes more prominent at speeds close to the speed of light. This lesson uses examples to explain space contraction and describes how space contraction accounts, in part, for the constant speed of light.

Space and Size

Space is just another name for size. To say something has space is to say it has dimensions that can be measured. For example, matter is defined as anything that has mass and takes up space. I don't know if size matters, but certainly matter has size - that is, space. We can think of space as having three dimensions - height, width, and depth. We can easily measure each dimension with a ruler.

Here's a question that will boggle your mind. Will the same object have the same measure of size regardless of its position or the position of the person doing the measuring? For that matter, will the size of the ruler always be the same regardless of perspective? As it turns out, the answer to each of these questions is no. Scientists have proven that the length of an object decreases when it is moving at high speeds. The shortening of distance at high speeds is referred to as space or length contraction.

Length Contraction

Let's look at an imaginary example of length contraction. Imagine you're at an air show to see the latest jet travel at a speed close to the speed of light. That I know of, no plane can currently come close to the speed of light, but like I said, this is an imaginary example. Furthermore, let's say you have the ability to measure the length of the jet as it passes by. As the jet passes by the first time, you clock its speed at 1000 kilometers per hour. Let's say you could actually measure the length of the jet as it passes by. When the jet travels at 1000 km/hr, you measure its length as 10 meters.

With the next pass, the jet is traveling at a speed close to the speed of light. Would you measure its length to be 10 meters? As it turns out, the length of the jet would measure shorter than 10 meters. Objects decrease in size in the same direction they are moving. In other words, length is relative to the state of motion of the object and the observer.

It's important to note that the pilot would measure the plane to be 10 meters as she is traveling at the same speed of the plane. From the pilot's perspective, nothing changes. Once again, length is relative to the state of motion of the object and the observer. We don't notice length contraction in our everyday life as nothing we see comes anywhere close to the speed of light.

Length Contraction and the Speed of Light

It's important to note that the speed of light is constant regardless of its source and the position of the observer. The speed of light is always c, which is 299,792 km/sec. The speed of light does not follow the rules of what we call classical relativity, which explains how velocities are different depending on the relative position of the observer. This apparent inconsistency of light speed with relativity begs the question - 'How can light have a constant velocity regardless of the observer's perspective?'

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