The Story of the Oily Brickpusher

What is follows is some sort of rant about the 'things experience the same acceleration due to gravity regardless of their mass' feature of the universe. (NEGLECTING AIR RESISTANCE, and any other troublesome forces.)

Some physics ideas

A force applied to a mass will cause it to accelerate - that is, change the direction something is moving in and/or its speed.

For the same acceleration, a thing with more mass requires a greater application of force. This is part of the reason you don't see airliners being driven by the single small propellor of a light aircraft.

The following sort of thing is going on here: if you double the force on an object, you double the resulting acceleration. Triple the force, and triple the acceleration you will get. This is summarised MATHEMATICALLY (oh no!) in the following expression:

FORCE = MASS x ACCELERATION

I drag this in here so you can play around with this concept. Try keeping one of the three things constant and see what happens when you change one of the other things. For instance, if you double the MASS, the ACCELERATION must be halved if the FORCE is the remain the same.

ANYWAY, this relationship says nothing about what is causing the force, which might have some interesting features itself. The features of GRAVITATIONAL force, for example, lead to the idea that, in the absence of other forces (such as air resistance), a truck and a tennis ball dropped from the same height will hit the ground at the same time. What follows is a tale of excitement and misdeed, and hamfisted illustration of a physical idea.

The Story of the Oily Brickpusher

Imagine oiling up a table to the extent that a brick will happily slide across it when pushed. You have fun all afternoon pushing the brick around on the table, making it fall off the edges, next you invite friends around with their bricks and you set up all sorts of collisions, film them, put them on the internet etc etc etc. Eventually your friends go home, leaving you exhausted, and with a pile of oily bricks. You look at what your life has become and decide to give up your rampant, partyhuman lifestyle.

Discipline replaces hedonism. Abandoning the reckless brick collisions of your youth, you decide to perfect your oily brick-pushing. Now all of your energies are devoted to accelerating the brick to a certain speed. With dedication, you manage to learn to apply just the right amount of force to send the brick sliding along the table at the same speed every single time.

Eventually, your quest for mastery of brickpushing leads you to start pushing stacks of two bricks to accelerate them to the same target speed. After years of perfecting your technique, you realise that it takes exactly twice as much force to get this happen. Further meditation reveals to you that the push required would increase in proportion to the number of bricks being pushed. In 2045, old, and so wizened to be barely recognisable as human, you wow mall shoppers by making a stack of five oily bricks accelerate exactly as much as a single oily brick. Your secret: you pushed the stack five times as hard as the single brick.

Not a single brick was oiled that day. Your story would serve as an inspiration to all those on the road to harnessing both mind and matter to achieve inner peace. However, your enlightenment would only be complete in your final moments. After a dazzling demonstration of a six-brick slide across the roof on roof of a seven-hundred storey residential megastructure, you slip on a particularly oily patch and end up clinging to the balcony rail of an apartment a few floors down. Through the window you see an old holovid of an Apollo astronaut dropping a feather and a hammer on the Moon. Simultaneously with their impact, your lose your grip and plummet,realising that all of your accomplishments in brick pushing have had nothing on gravity's unseen hand. Without so much as an oily tabletop, gravity has been doing the same thing with bricks and all other objects - though unlike yours, its push does not cease at an arm's length.

This gravitational force, which even now attracts you towards the Earth's centre grows in proportion with increases in mass - such that if two of you were now stapled together, you would be pushed twice as hard. But, just as in your meddlings with bricks, the resulting acceleration would remain the same; the push is doubled, but so is the mass being pushed. As the busy streets below loom ever larger in your sight, you wonder if the Earth is also being pushed towards your centre.

Tragically, you only begin to contemplate the effects of air resistance a microsecond before the pavement claims you. Don't worry though - your demise leads to a review of rooftop safety in the presence of lubricants, and commemorative plaques will be installed at the key locations of your fall. Your story will be forever used as a crude analogy for the behaviour of gravitational forces.