Acceleration is defined as the rate of change of velocity.
The slope of a velocity time graph shows you your acceleration. If you have a constant slope for a velocity time graph, you have constant uniform acceleration.
An object in free fall will accelerate towards the Earth at a constant rate of -9.8 m/s/s.
We use the letter "g" to represent -9.8 m/s/s acceleration.
Bowling Ball Drop
1.) http://www.sciencealert.com/watch-a-bowling-ball-and-feather-fall-in-world-s-biggest-vacuum-chamber
http://dev.physicslab.org/document.aspx?doctype=3&filename=kinematics_derivationkinematicsequations.xml
http://www.physicsclassroom.com/Class/1DKin/U1L4a.cfm
http://hyperphysics.phy-astr.gsu.edu/hbase/Mechanics/motgraph.html
https://www.youtube.com/watch?v=f3xeOA6MMDc
http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/explaining_motion/describingmotionrev3.shtml