How fast are you moving right now? This may seem like a straightforward question, but the answer is far from simple. You might initially think, “I’m not moving.” However, upon further reflection, you may consider the Earth’s motion. This could lead to a second answer, “19 miles/second around the Sun.” But then, you might remember that the Sun moves around the center of the Milky Way galaxy, and the Milky Way moves within the Local Group of galaxies, and so on. Thus, the question “How fast are you moving?” is not as easy as it first appears.
When Mission Control informs astronauts of their speed, there’s always an assumed standard of rest. Initially, speeds are given relative to the launchpad. However, as the journey progresses and the launchpad becomes just another arbitrary place on Earth’s spinning surface, speeds are given relative to the idealized, non-spinning pinpoint center of Earth. This highlights the complexity of answering the question, “How fast are you moving?”
Speed is a relative quantity. For instance, when Captain Kirk asks Lieutenant Sulu if the Starship Enterprise has reached a speed of warp 7, Sulu should reply, “Relative to what, Captain?” This response, while potentially troublesome for Starfleet officers, is the only accurate answer to the question, “How fast are you moving?” This concept is not based on Einsteinian relativity, but on Galilean relativity, which asserts that there is no such thing as an absolute speed. Speeds are relative, meaning they only have meaning when referred to a reference frame.
Even the concept of rest is relative. Earth’s speed is 19 miles/second relative to the Sun. The Enterprise’s speed is warp 7 relative to the center of the Milky Way galaxy. Your speed is zero relative to your easy chair. However, depending on where you sit, it could be hundreds of miles/hour relative to Earth’s center. When we ask, “But how fast is Earth really moving?” we imagine Spaceship Earth plowing through the ocean of space as it orbits the Sun. But space is not an ocean. It has no substance like water. Space is not a thing; space is nothing. You can move between two points in space, but you can’t move through space. There’s nothing to move through.
Some motions have only relative meaning, but some motions have absolute meaning, are absolutely real. For example, constant speed is relative, but change in speed is absolute. When your spaceship fires its engines, your change in speed is beyond doubt. You feel it in your stomach, and your ship’s sensors can measure it. The same goes for rotation. If your spaceship is spinning, you can feel it, and your ship’s sensors can measure it. So, some motions are relative, and some are not. There is no deep reality about constant speed, but changes in speed are deeply real, and so are rotations.
We have to be thoughtful in our analysis of everyday experience in order to identify what is deeply real. Since we can be fooled by perceptions as basic as speed, maybe every perception deserves careful scrutiny. This is what inspired Einstein to his incredible insights about the speed of light and forward time travel. Knowing how to identify what is deeply real is tough and important work. If a police officer ever pulls you over for speeding and asks, “Do you know how fast you were going?” an insightful, though perhaps unwise, reply would be, “Relative to what?” And then, as you sit in the backseat of the police car and feel it accelerate toward jail, you can add, “But some things are absolute!”
Conduct an experiment to understand relative speed. Use toy cars and a marked track. Measure the speed of a car from different reference points: a stationary observer, a moving observer on another car, and an observer on a rotating platform. Record and compare the speeds to see how they change based on the reference frame.
Draw a diagram showing the different motions discussed in the article: Earth’s rotation, Earth’s orbit around the Sun, the Sun’s orbit around the Milky Way, and the Milky Way’s movement within the Local Group. Label each motion with its speed and discuss how these speeds are relative to different reference points.
Split into groups and hold a debate on the topic: “Is there such a thing as absolute motion?” One group will argue that all motion is relative, while the other will argue that some motions, like changes in speed and rotation, are absolute. Use examples from the article to support your arguments.
Solve a series of problems that involve calculating speed from different reference frames. For example, calculate the speed of a person walking on a train moving at a certain speed relative to the ground. Then, calculate the speed of the train relative to the Earth’s center. Discuss how these calculations illustrate the concept of relative speed.
Write a short essay on how our perception of speed can be misleading. Use the example of sitting in a chair versus moving with the Earth and the galaxy. Reflect on how understanding relative motion can change our perception of everyday experiences and the importance of questioning what we perceive as reality.
Understanding – The ability to comprehend or grasp the meaning of something. – I have a deep understanding of the topic after conducting extensive research.
Speed – The rate at which something moves or operates, or how fast something travels. – The cheetah is known for its incredible speed, reaching up to 70 miles per hour.
Fast – Moving or capable of moving at high speed. – The sports car accelerated so fast that it left all the other vehicles behind.
Moving – Changing or capable of changing position. – The movers carefully loaded the furniture onto the truck before moving it to the new house.
Relative – Considered in relation or in proportion to something else. – The price of the product is relative to its quality.
Rest – The state of not moving or being active. – After a long day at work, I like to rest and relax at home.
Quantity – The amount or number of something, usually measurable. – She purchased a large quantity of oranges to make fresh juice for the party.
Relativity – The concept in physics that the laws of nature are the same for all observers in uniform motion. – Albert Einstein’s theory of relativity revolutionized our understanding of space and time.
Motion – A change in position or location, or the act of moving. – The waves of the ocean were in constant motion, crashing against the shore.
Absolute – Not dependent on anything else; total or complete. – The dictator had absolute power over the country and made all the decisions.
