cm [001] motion & velocity

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MOTION & VELOCITY

CM [001]

In search for the cause of motion


Motion in the Observable World

In daily life motion is evident when things are moving. Everywhere we see: people move; birds fly. In the cosmos, the sun and moon rise and fall; planets twirl around stars; galaxies whistle through space.

Time moving

Birds moving

Earth moving Sun moving

Galaxies moving

Man moving


Motion in the Microscopic World

Not only that, it has been proven beyond doubt that all the small material bodies in this universe are in a state of motion: molecules vibrating; electrons orbit around nuclei; neutrinos fly in every direction; quarks and gluons twitching inside the elementary particles.

Cells moving

Molecules moving

Atoms moving Quarks moving


Definition of Motion

The word ‘motion’ came from the Greek word ‘motus’ which means change. In ancient Greece, motion includes fluxes, growths, meltings, coolings, heatings . . . etc. The ancient Greek philosophers recognized that the world is transient and is constantly changing.


Translational Motion

To be more precise and scientific in physics, by motion we mean the change of position in space, that is, ‘translational motion’.

Translational motion

Changes


Speed

In translational motion, speed is the perception of how fast an object moves. The concept is a simple one and was well known in the early civilizations or even in prehistoric times. In fact it is so simple that its origin is never noticed.

Slow = Low Speed Fast = High Speed


Ancient Greeks on Speed

Serious consolidation of the concept of motion may have been started with the ancient Greek philosophers when they began to ponder upon the phenomenon of objects in motion.

For example, the great philosopher Aristotle (384–322 BC) had his own notion of motion in that time is proportional to the distance moved. He said:

“For at any moment when a thing is causing motion, it also has caused motion, so that there must always be a certain amount of distance that has been traversed and a certain amount of time that has been occupied.” Aristotle’s Physics VII.

The idea of speed


Galileo’s Investigation

It was probably Galileo Galilee (1564-1642) who first developed the conception of motion in definite and quantitative terms. Through his various investigations such as the slide experiment, he used the mathematical notion of velocity as distanceover a period of time.

Dripping water to count time

Ball rolling down slide

Slide tilted to have different angles

𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦= 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 ÷ 𝑇𝑖𝑚𝑒


Units of Distance & Time

Distance and time are two independent quantities, each with their own measurement units. Distances are measured in cm, m, km etc., in the metric system and inches, feet, miles in the imperial system. For convenience, the metric system is used throughout in our discussions with imperial units in brackets if necessary.

Time is more universal. It is measured in seconds, minutes, hours, days, etc. which we are familiar with.

Distance units in cm, m, km, etc.

Time units in second, minutesHours, days, etc.


Equation for Velocity

For the special case of uniform motion in which an equal distance (∆𝑥 = 𝑚𝑎𝑙𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒) is covered in equal interval of time (∆𝑡 = 𝑠𝑚𝑎𝑙𝑙 𝑡𝑖𝑚𝑒), it can be written as:

𝑈𝑛𝑖𝑓𝑜𝑟𝑚 𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑣= 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (Δ𝑥)÷ 𝑇𝑖𝑚𝑒 Δ𝑡

Or simply in pure mathematical form:

𝑣 =Δ𝑥

Δ𝑡

𝒗 =𝜟𝒙

𝜟𝒕


Geometric Representation of Speed

Since distance (space) and time are two independent quantities, we can represent them by the two perpendicular coordinates of a Cartesian coordinate system: y-axis take up distance and x-axis looks after time. Velocity become the slanting line or slope across space and time.

Thus speed is measured by meters or feet per second, kilometres or miles an hour.

By interposing, we have the distance:

Δ𝑥 = 𝑣Δ𝑡

Dis

tanc

e (s

pace

)Time

Δ𝑥

Δ𝑡

𝑣 =Δ𝑥

Δ𝑡


The Kinematic Piece

Galileo’s kinematics was accepted by physicists in the subsequent centuries and became the basis of Newton’s work and the foundation of classical mechanics.

Velocity


ARISTOTLE ON MOTION

To be continued on PM [002]:

cm [001] motion & velocity

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