# What Is This Motion?

Table of Contents

## What is Motion?

Motion is the action of changing location or position. It is one of the most fundamental concepts in physics that describes how objects move through space and time. Motion can be seen all around us – from a bird flying through the sky, to waves crashing on a beach, to a child swinging on a playground.

In everyday life, we observe many types of motions:

• Linear motion – Moving along a straight line, like a car driving down a straight road.
• Oscillatory motion – Back and forth motion around an equilibrium point, like a pendulum swinging.
• Circular motion – Moving in a circular path, like a Ferris wheel rotating.
• Rotational motion – Spinning around an axis, like a spinning top or the Earth rotating on its axis.
• Periodic motion – Motion that repeats in cycles, like the motion of a spring or the orbit of the moon around Earth.

These are just some examples, but motion can take on countless forms. Fundamentally, motion requires an object to change its position compared to a reference point. Understanding motion provides insight into the underlying physics that governs our universe.

## Causes of Motion

Motion occurs when an object changes its position relative to a frame of reference. All motion requires a force – a push or pull upon an object. Forces cause acceleration, which is defined as a change in velocity over time. According to Newton’s First Law, an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

There are different types of forces that can cause motion. Some examples include:

• Friction – The force that resists motion when two surfaces are in contact.
• Tension – The pulling force transmitted axially through a rope, string, cable, or wire when it is stretched tight.
• Gravity – The attractive force between two objects that depends on their masses and the distance between them.
• Magnetism – The force between magnetic objects that either attract or repel.
• Thrust – The propulsive force that pushes an object in the opposite direction.

Newton’s Second Law states that force equals mass times acceleration (F=ma). This means that a larger force applied to an object will produce greater acceleration. Newton’s Third Law states that for every action, there is an equal and opposite reaction. So when you push or pull on an object, it pushes or pulls back on you with an equal force in the opposite direction.

Understanding the forces and Newton’s Laws that cause motion allows us to predict the motion of objects and utilize motion in many useful applications, from throwing a ball to launching rockets into space.

## Measuring Motion

Motion can be quantitatively measured using concepts like displacement, speed, velocity, and acceleration.

Displacement measures the change in position of an object. It refers to the distance between an object’s initial and final position. Displacement only considers the endpoints, not the path traveled between them.

Speed measures how fast an object is moving. It is calculated by dividing the total distance traveled by the time elapsed. Speed does not account for direction.

Velocity measures speed in a specific direction. It is calculated by dividing an object’s displacement by the time taken. Velocity measures both speed and direction.

Acceleration measures the rate at which velocity changes over time. An increasing velocity results in positive acceleration, while a decreasing velocity leads to negative acceleration. Acceleration can be calculated by dividing the change in velocity by the time taken.

Some examples of calculating motion measurements:
– A car travels 120 km east in 2 hours. Its displacement is 120 km east, its speed is 60 km/hr, and its velocity is 60 km/hr east.

– A ball is rolled down a ramp, covering 10 meters in 5 seconds. Its speed is 2 m/s (10 m / 5 s), and if rolled downwards, its velocity is 2 m/s downwards.

– A train accelerates from 20 km/hr to 80 km/hr in 10 seconds. Its acceleration is 6 km/(hr*s) [(80 km/hr – 20 km/hr) / 10 s].

## Frames of Reference

Motion is always measured relative to some frame of reference. The frame of reference is the system or point from which motion is measured. There are two main types of frames of reference:

### Absolute Motion

Absolute motion refers to motion measured relative to a fixed, universal frame of reference that is considered to be at rest. In classical physics, absolute space and time provided the fixed frame of reference for measuring absolute motion. However, we now know that there is no fixed, universal frame of reference that can determine absolute motion.

### Relative Motion

Relative motion refers to motion measured in relation to some other object or frame of reference. All motion is relative – the motion of an object depends on your frame of reference. For example, a car traveling at 50 mph relative to the road is at rest relative to a passenger sitting inside it. Both are valid frames of reference to measure the car’s motion.

The relativity of motion was popularized by Galileo’s ship thought experiment. Imagine sailing on a ship moving smoothly across the sea. Below deck, there are no windows and no way to tell the ship is moving. Any experiments done below deck will give identical results whether the ship is moving or at rest. Motion is only meaningful when measured relative to some external reference frame.

Because motion is relative, different observers can measure different motions depending on their frames of reference. This is why there is no fixed, universal frame of reference that can determine absolute motion.

## Types of Motion

There are several main types of motion that objects and systems exhibit in physics:

### Linear Motion

Linear motion is motion in a straight line. The position of an object changes uniformly with respect to time. Examples are a car moving down a straight road at constant speed or an object in free fall acceleration due to gravity.

### Oscillatory Motion

Oscillatory motion is repetitive back and forth motion around an equilibrium point. Examples are a mass on a spring oscillating up and down after being displaced, or a pendulum swinging back and forth.

### Circular Motion

Circular motion is movement in a circular path at constant speed. Examples are the motion of planets orbiting the Sun and wheels rotating at a fixed rate.

### Rotational Motion

Rotational motion is motion around an axis or center point. Examples are a spinning top, a wheel turning, or the Earth rotating on its axis.

### Periodic Motion

Periodic motion is repeating motion that occurs at regular time intervals. Oscillatory and circular motion are periodic. The time for one complete cycle is called the period.

Motion graphs plot an object’s position, velocity, or acceleration over time. Analyzing the slopes and shapes of the graphs allows interpretation of the type of motion.

## Motion in Our Universe

Motion occurs throughout our universe, from the smallest subatomic particles to entire galaxies. On the largest scales, galaxies and galaxy clusters are constantly in motion, influenced by gravity and the expansion of the universe. Galaxies orbit around each other and collide over billions of years. Within galaxies, stars orbit around the galactic center, bound together by gravity.

Our solar system exhibits motion on a smaller scale. The planets orbit the Sun due to gravity, inertia, and centrifugal force. Even though the Sun’s gravity pulls the planets inward, their inertia keeps them moving forward in their orbits rather than falling into the Sun. The centrifugal force caused by their orbital velocity also counteracts the Sun’s gravity. The planets closest to the Sun orbit faster than those farther away. Mercury completes a full orbit in only 88 Earth days, while distant Neptune takes 164.8 years. Moons also orbit planets, like our own Moon orbiting Earth.

The motion of celestial bodies follows the laws of physics, though it can be difficult for humans to grasp such large distances and timescales. The universe provides an enormous laboratory for observing motion on the grandest scales imaginable.

## Applications of Motion

Motion principles find widespread application in many areas of everyday life including transportation, sports, medicine, engineering, and more. Understanding concepts of acceleration, velocity, momentum, and frames of reference allows us to improve designs and make new discoveries.

In transportation, the study of motion helps engineers design vehicles that can travel faster while expending less energy. Streamlining vehicle shapes reduces drag and friction, allowing for greater speeds. Suspension systems are engineered to smooth out bumps in the road. Brakes apply friction to slow momentum and bring vehicles to a stop.

In sports, athletes study motion to perfect their techniques. A golfer analyzes their swing to generate maximum club head speed. A diver performs spins and twists by controlling the moments of inertia of their body. Sports scientists help design equipment like tennis rackets and golf clubs that maximize power and control.

In medicine, an understanding of biomechanics and motion helps doctors treat injuries and improve function. Analyzing gait can aid in designing prosthetic devices. Physical therapists apply motion techniques to restore mobility and reduce pain. Surgeons use robotics and instrumentation that rely on motion principles.

Across many engineering domains, machines and mechanisms are designed around motion and dynamics concepts. Linkages, gears, pulleys, and drives all aim to transfer force and transform motion in useful ways. Buildings and bridges rely on structural dynamics to withstand seismic shaking and wind loading.

In diverse fields, a grasp of motion fundamentals empowers discovery and drives innovation every day. Real-world examples show that motion principles find application anywhere objects move, forces act, or work is done.

## Famous Discoveries

Throughout history, there have been many key figures that made groundbreaking discoveries related to motion that transformed our understanding of physics and the universe. Three of the most influential were Galileo Galilei, Sir Isaac Newton, and Albert Einstein.

Galileo Galilei was an Italian astronomer, physicist and engineer who made pioneering discoveries in the early 1600s. He greatly improved the telescope and used it to make several major astronomical observations, like discovering moons orbiting Jupiter. Galileo also performed experiments with inclined planes and pendulums, quantifying gravity’s effects on motion. His study of motion laid the foundations of modern physics. Galileo supported the heliocentric model proposed by Copernicus, which placed the sun at the center of the universe. The Catholic Church forced him to recant this view, which was deemed heretical at the time.

Sir Isaac Newton was an English physicist and mathematician who lived in the 1600s. Newton developed the three laws of motion that are the foundation of classical mechanics. These laws describe the relationship between a body and the forces acting upon it, and how it moves in response. The laws explain inertia, acceleration, force, and action-reaction pairs. Newton showed that the motions of physical objects on earth and celestial bodies are governed by the same set of natural laws. His book “Philosophiæ Naturalis Principia Mathematica” laid the groundwork for classical physics.

Albert Einstein was a German-born theoretical physicist who lived in the early 1900s. Einstein revolutionized physics with his general theory of relativity, which described gravity as a geometric property of space and time. His famous equation E=mc^2 showed that energy and matter are interchangeable. Prior to Einstein, scientists thought of energy and matter as distinct. Einstein also made major contributions to the development of quantum theory. His work showed light could be viewed as both waves and particles. Einstein’s ideas fundamentally changed our understanding of time, space, matter, energy, and gravity.

The pioneering discoveries of Galileo, Newton, and Einstein related to motion provided the foundation for modern physics. Their groundbreaking ideas and theories had an enormous impact on science, technology, and our understanding of the universe.

## Current Research

Some of the most exciting advancements in the study of motion are happening right now. Researchers around the world are making new discoveries that further our understanding of motion and open up possibilities for future technologies.

One area of focus is chaos theory and how it relates to motion. Chaos theory studies complex systems that are highly sensitive to initial conditions. This field looks at patterns in systems that appear random but actually contain hidden order and predictability. Understanding chaos theory can help describe irregular motion patterns like turbulence. It also has applications in fields like weather forecasting, technology, and more.

Quantum motion is another emerging field of study. This examines the motion of subatomic particles that behave according to the laws of quantum mechanics. Researchers are investigating questions like how quantum entanglement can enable interaction between particles at vast distances and how quantum tunneling allows particles to pass through barriers. Learning more about motion at the quantum scale could lead to breakthroughs in computing, cryptography, teleportation, and other technologies.

New propulsion technologies are also enabling different paradigms for motion. Advanced propulsion concepts like EmDrives, RF resonant cavities, magneto plasmadynamic thrusters, and more are being researched. If proven viable, these technologies could drastically improve space travel and transportation. The ability to propel spacecraft at a fraction of the fuel cost could open up deep space exploration and interstellar travel.

While motion itself is not a new phenomenon, we are still finding new insights into how it works at every scale. From particle physics to rocket science, motion continues to be an exciting field of discovery with profound impacts on technology and society.

## Summary

Motion permeates every aspect of our universe. Whether we’re talking about the planets orbiting the Sun, a spinning galaxy, or the blood circulating in our bodies, everything in this dynamic universe is in motion. In this article, we explored the causes and measurements of motion, different frames of reference, and the various types of motion we observe, from linear to circular to harmonic. We also discussed examples of motion on both cosmic and microscopic scales.

Some key takeaways include:

• Motion requires a force. Forces like gravity, electromagnetism, friction, and thrust from engines or muscles drive the motion we see.
• Motion is relative. An object’s motion depends on the frame of reference from which it’s observed.
• Velocity describes speed and direction. Acceleration refers to a change in velocity over time.
• Apart from linear motion, objects often move in curves, circles, vibrations, and rotations.

Without motion, our universe would be static and unchanging. Motion drives everything from the cycles of life to the mechanisms of the cosmos. Our understanding of motion has unlocked many mysteries and enabled incredible technologies. Ongoing research continues to reveal intriguing new details about motion in its many manifestations. By studying motion, we come to appreciate the dynamic, interconnected nature of our universe.