Physics is concerned with the motion of objects and quantitative analysis of motion.
Everything is in constant motion, complicating the analysis of motion.
Understanding Motion Context
Example: A car traveling at 100 km/h ignores the Earth's rotation (~1,700 km/h at the equator) and movement through space (30 km/s around the Sun).
The solar system moves around the galactic center at 20 km/s, and the Milky Way moves through the universe at 230 km/s.
In certain contexts, there is little difference between flying in a plane and being at rest.
Relative Motion vs Absolute Motion
We often discuss motion relative to the Earth's surface (inertial reference frame).
Example: A car moving at 100 km/h is moving relative to the ground.
Inside the car, it feels stationary while the surroundings move at 100 km/h.
Inertial Reference Frame
An inertial reference frame is an object, person, or location treated as stationary to assess the motion of other objects.
Example of a moving train: A ball thrown straight up appears to follow a parabolic path to an observer on the ground due to the forward velocity of the train.
Importance of Frames of Reference
Understanding frames of reference is crucial in physics.
Galileo's experiments on a moving ship demonstrated that objects behave similarly irrespective of the reference frame.
He showed that a dropped ball falls straight down regardless of the ship's motion.
Galileo's Contributions
In 1632, Galileo published "Dialogue Concerning the Two Chief World Systems."
He proved that velocity measurements depend on the chosen frame of reference.
Galileo's work led to the concept of Galilean relativity.
Implications of Relative Motion
The Earth could be moving without us feeling it, contrasting earlier beliefs.
Galileo's ideas eventually faced opposition from the Catholic Church but laid the groundwork for modern physics.
Conclusion
The concept of relative motion is foundational for future topics in physics, such as Einstein's special relativity.
Despite Earth's motion, it serves as a good approximation of an inertial reference frame.