Drawing

DEPCOllc
800.767.1062 | www.depcollc.com | © 2013
3305 Airport Drive | Pittsburg, KS 66762
S3
Gravity Revisited: A Force to Reckon With (SI Units Only)
Mass and weight are used interchangeably in daily life. For practical purposes the force of
gravity over the earth’s surface is considered to be constant. (It actually varies with respect to
altitude or distance from the earth’s center and local variations in density.) Weight and mass are
equivalent expressions when the force of gravity is considered to be constant.
Galileo reasoned that gravity is a force that acts continuously on all objects. He experimentally
determined that free falling masses do not fall at a constant velocity. Simply put, the force of
gravity caused falling masses to accelerate, and this rate of acceleration could be measured.
Newton, who ironically was born on the day Galileo died, created the mathematical models to
quantify and predict the implications of the gravitational forces that Galileo had measured.
Newton described the essential relationship between force, mass and acceleration and produced
an elegantly simple statement that explains the movement of objects in the physical universe.
onAccelerati*MassForce
Where:
Force is expressed in units called Newtons.
Mass is measured in Kilograms (kg).
Acceleration is expressed in meters/sec.
2
(m/s
2
).
Gravity x Mass = Weight
Newton’s simple algebra provides a convenient way for us to differentiate between mass and
weight. We can substitute the quantities above to predict the weight (Force) exerted by a given
mass on earth.
Weight = Mass * Acceleration of Gravity
Where:
Weight is a downward force
expressed in units called
Newtons.
Mass is measured in
Kilograms (kg).
Acceleration is expressed in
meters/sec.
2
(m/s
2
).
Weight or Force = Mass*Acceleration
Weight or Force = 80kg*9.8meters/s
2
Weight or Force = 784 Newtons
Mass = 80 Kilograms
80kg
Force or Weight = 784 Newtons
Gravity = 9.8 Meters/s
2
Sample Science Curriculum