Hopetoun Falls, Beech Forest, near Otway National Park, Victoria, Australia.
Credit: Wikipedia contributor David Iliff. According to Wikipedia permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version.
Download site: Wikipedia: Image:Hopetoun falls.jpg.
Sections
The symbol for this scalar quantity is g and the units are m/s**2=N/kg.
The equatorial bulge and other effects give a 9.780 N/kg to 9.832 N/kg equator to pole variation at sea level.
There is also a variation with altitude (Wik: g(y)). Note Mt. Everest goes up to 8.848 km above sea level.
The standard gravity
set by convention is g_0=9.80665 N/kg. It's a conventional average.
The mean spherical non-rotating Earth g=9.823 N/kg (my calculation).
In intro classes, one usually just uses g=9.8 N/kg as a fiducial or reference value.
A couple of example motions are shown in the animations: rectilinear motion and parabolic trajector motion.
Both of these cases are free-fall motions: motions where gravity is the only force acting on the moving body---air resistance is turned-off
Scroll down to the two animations.
Here 4 of them are just being flashed at out---but you'll soon know them like the back of your hand.
Actually, I believe that there are 5 kinematic equations.
This may get ahead of your calculus class, but we have to do a little differentiation and integration or antidifferentiation to derive kinematic equations for constant acceleration in one-dimension.
One needs algebra which can be tricky
Differentiation is finding the slopes of curves.
Integration is finding the area under curves.
In conception, integration is a limiting process in finding the area from a converging sequence of Riemann sums.
Typically, air resistance can be neglected if the object is dense and the drop relatively short.
For example in Galileo's Leaning-Tower-of-Pisa experiment.
He is thought have dropped two cannon balls of different mass.
Galileo probably actually did this experiment, but it was probably more of a demonstration for the onlookers than a real experiment.
The balls didn't actually hit the ground at the same time.
``Galileo's'' point was that they would do so ideally if all complicating effects were eliminated.
This ideal way of looking at things is the path of modern physics---and many other sciences.
Find the ideal, underlying laws and then understand the actual world in terms of them allowing for complicating effects and measurement uncertainties.
The symbol for this scalar quantity is g and the units are m/s**2=N/kg.
The equatorial bulge and other effects give a 9.780 N/kg to 9.832 N/kg equator to pole variation at sea level.
There is also a variation with altitude (Wik: g(y)). Note Mt. Everest goes up to 8.848 km above sea level.
The standard gravity
set by convention is g_0=9.80665 N/kg. It's a conventional average.
The mean spherical non-rotating Earth g=9.823 N/kg (my calculation).
In intro classes, one usually just uses g=9.8 N/kg as a fiducial or reference value.
When falling cats first right themselves into landing position. The cat righting reflex does this.
In long falls, they stretch out to increase their air resistance. This may be instinctive or because they become relaxed.
A cat tucked in has a terminal velocity of about 27 m/s and spread out of 19 m/s (HRW-105).
This is the theory anyway.
There seems to be some question about it.
Controled experiments are needed.
The cats appearing in the video (made at the Institute of Cat Physics) gave their informed consent.
What is terminal velocity you say?
I'm glad you asked that question.
The force of air resistance increases with velocity and points opposite velocity.
Therefore air resistance increases with speed and in long falls there comes a point where air resistance practically balances gravity and the object (e.g., the cat) reaches terminal velocity.
