Lesson 7: The History Of Motion
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The History of Motion
What is physics?
Physics is the science of matter and energy. Matter is any physical substance you can touch. Energy in physics is the capacity for doing work.
Physics tries to help us make sense of the world and the universe that we live.
Today there are two branches of physics, classical and modern.
Classical physics includes everything physicists discovered before the 1900s, also known as Newtonian Physics, named after Isaac Newton. Modern physics came about because scientists started seeing things that Classical Physics said should not be happening.
Modern physics refers to the Theories of Relativity developed by Albert Einstein and Quantum Physics which was developed by many scientists, including Einstein, and is still being developed today.
Don’t make the mistake of thinking classical physics is obsolete. Classical physics is needed for everything from cooking supper to driving your car.
Relativity says it doesn’t matter where you are; the laws of physics are the same for you as for everyone else. If you are on another planet and I am on earth, physics is the same for both of us. If you are in a rocket ship zooming to the moon and I am sitting in a chair in my house on earth, physics is the same for both of us.
Quantum physics deals with the universe at microscopic levels, and it says everything is chunky. The universe consists of bundles of matter and energy. The universe comes in chunks.
This tells us the universe is not deterministic. This will not happen. It has a 0% chance. This may happen with a 58% chance. This happened; 100% chance. The universe went from being thought to be deterministic to statistical.
Again, relativity means the laws of physics are the same for everyone, no matter where they are or how they are moving. Picture yourself and two friends. Picture yourself standing on the ground. Picture one friend drives past very fast in a car. Picture your other friend zooming even faster over your head in an airplane. Now picture all three of you throwing a ball straight up directly over your heads and catching it as it falls back down into your hand. Notice it doesn’t matter where you are at or how you are moving you all three get the same result. The ball, if thrown directly above your head, falls straight back down into your hand.
If some of what we have said seems a little vague right now, that is okay. It will make a lot more sense as we go through more lessons.
We are going to change pace for a minute and talk about motion.
What is moving?
Motion is going from one location to another in time. You drive from home to work or school in a certain amount of time.
Here is a question to think about?
Is it normal for something to be motionless, not moving, in a state of rest, or is it normal for something to be constantly moving until something affects it?
Let’s answer this question by going over some physics history.
It was once believed the earth and heavens had different laws of physics.
It was believed that the earth was the center of the universe, and everything was drawn to the center of the universe. That is why when you drop something, it falls to the ground.
They thought everything in the heavens moved in perfect circles. Everything continued in motion and did not come to a state of rest. The Greek philosopher Aristotle believed the earth was the center of the universe. The sun and planets revolved around the earth in perfect circles.
This was the belief for thousands of years until Nicholas Copernicus in 1543 said the sun was the center of the universe, not the earth. The earth and planets revolved around the sun. This showed the earth was not special. You can understand why this was not very popular with the church at the time, and if you found yourself at odds with the church, you could find yourself in a dangerous situation.
Galileo Galilei was next on the physics scene.
Galileo loved astronomy, and he developed the first telescope. Through his telescope, he saw the planet Jupiter and its moons revolving around it. Here was another “little” universe.
Again, he showed the earth was not special.
It was said Galileo dropped objects off The Leaning Tower of Pisa to show objects fall to earth with the same acceleration, speeding up at the same rate.
Galileo believed an object moving in a straight line at a constant speed without friction would never stop. The natural state of motion is to move in a straight line at a constant speed. It doesn’t take a push to get something moving. It takes no force to keep something moving.
This is known as the Law of Inertia. A natural tendency to keep moving at a constant speed. Doesn’t seem true to us or is hard to see because of friction. Friction is the resistance that one surface or object encounters when moving over another. A change in motion means a push or pull has occurred.
The next person to take the physics state was Isaac Newton. He is considered by most to be the greatest physicist who ever lived, even better than Einstein.
Isaac Newton developed the three laws of motion.
1. The Law of Inertia – An object moves in a straight line and constant speed unless acted upon by an outside force.
2. F=ma – Force equals mass times acceleration. This basically says the bigger the object, the harder it is to get it moving or stop it from moving. Another way to look at it is the faster something is moving or the bigger it is, the more force it will generate. Think of a bullet fired from a gun. It is small, but it accelerates really fast, so it has a lot of force. Think of a slow-moving big semi-truck. It may be moving slowly, but because it is big, it still has a lot of force.
3. Every action has an equal and opposite reaction. If you push on a wall with force, the wall pushes back with the same force.
This led to the belief in a clockwork universe, which means everything is deterministic. If it were possible to view everything in the universe, you could predict every future event. It was like something wound up the universe and set it off in a very predictable way. Everything that happens is predictable. There is no free will. Luckily, we have Quantum Physics to save us from that bleak future.
You have probably heard the story Newton sat under an apple tree, and an apple fell to earth, hit him on the head, and he discovered gravity. There was probably more to it than a falling apple, but Newton discovered the Law of Gravitation.
Most of the time, when someone describes gravity, they say what goes up must come down. This is not exactly true. What is happening is every object attracts every other object depending on the mass and how far apart they are. The bigger the object, the more the attraction. The closer you are to an object, the more the attraction. The force of gravitational attraction is directly dependent upon the masses of both objects and inversely proportional to the square of the distance between their centers. To put it in numbers, if you double the distance between two objects, the gravitational attraction is one-fourth of what it was. At five times the distance, the gravitational attraction is only one twenty-fifth the original attraction.
Newton invented Calculus, so he could use the Law of Gravitation to describe the motion of planets.
It is usually the belief that Einstein came up with the idea of relativity. Relativity was already known before Einstein came on the scene. It was Einstein who discovered what was to become known as Special Relativity, but it was Newton’s Laws of Motion and Gravitation which showed the laws of physics apply everywhere in the universe. The is no special place where the laws will ever differ.
The laws of physics work the same for everyone in uniform motion. Uniform motion is moving at a constant speed in one direction — no accelerating.
If you are zooming hundreds of miles per hour in an airplane, you can still eat without your food smashing into your face unless you hit turbulence, then you are no longer in uniform motion. You are no longer moving in a straight line at a constant speed. The turbulence is moving the plane in crazy directions and speeding it up, and slowing it down.
I am moving is a meaningless statement. If a person driving a car sees a person standing on a road, it is just as accurate to say the person on the road is moving and you are still. As you drive down the road, does it not appear as if the road signs and lights and trees and people are moving past you?
Picture yourself in a school bus. Now cover all the windows (I hope you have a really good bus driver). As long as the bus moves straight ahead and does not change direction or speed, there is no experiment you can do to prove you are moving if you can’t see out the windows. Everything you do will be exactly the same as if you were doing it in your house.
To repeat what we said earlier. Relativity says it doesn’t matter where you are physics looks the same to you as it does for everyone else. It makes us all equal. There is no special place or state of motion. It doesn’t matter where you are. If you are on another planet, physics is the same for you as it is for me on earth. It doesn’t matter how you are moving. If you are in a rocket ship zooming to the moon, physics is the same for you as it is for me on earth. Relativity says there is no place in the entire universe that is special.
In the next lesson, we are going to learn about another part of classical physics called electromagnetism. It was because of a very unique property of electromagnetism that Einstein was able to develop his Special Theory of Relativity.
Once again, draw that picture and teach this to someone else.