Newton's Second Law
In the presence of a NET FORCE, an object experiences an ACCELERATION
directly proportional to the NET FORCE
inversely proportional to the MASS of the object.
-- F is the NET force
-- m is the mass which that net force acts on.
We often turn this around and write it as
F is the NET force acting on an object
m is the mass of the object which the force F acts upon.
What are the UNITS of force in
F = m a
A force of ONE unit
will give an object of 1.0 kg mass
an acceleration of 1.0 m/s/s ;
this force is known as
ONE NEWTON (1.0 N) .
1 N = ( 1 kg ) ( 1 m/s/s )
F = m a
Force will be measured in newtons
A force of 1 N will give
a mass of 1 kg
an accelertion of 1 m/s/s.
12 N = ( 3 kg ) ( 4 m/s/s ) A force of 12 N could give
a mass of 3 kg
an accelertion of 4 m/s/s
12 N = ( 2 kg ) ( 6 m/s/s ) A force of 12 N could give
a mass of 2 kg
an accelertion of 6 m/s/s .
We have already seen that all objects fall with the same acceleration, 9.8 m/s/s (which we approximate as nearly 10 m/s/s).
We call this free fall.
When such objects fall, the only force acting on them is their weight, the force of gravity.
The only force on a body in freefall is the force of gravity. We call this its weight.
Since it accelerates at 9.8 m/s/s,
that weight must be
w = (mass ) x (9.8 m/s/s),
w = m g
The weight of an object is the force of gravity on that object.
Weight, since it is a force, will be measured in units of newtons (N).
Mass will be measured in kilograms (kg).
If an object is in equilibrium -- at rest -- then, the net force on the object must be zero.
That is, the sum of all the forces on an object is zero when the object is in equilibrium.