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Newton’s 2nd Law
Newton's second law of motion
pertains to the behavior of objects
for which all existing forces are not
balanced.
Newton’s Second Law
The second law states that the acceleration of
an object is dependent upon two variables - the
net force acting upon the object and the mass of
the object. The acceleration of an object
depends directly upon the net force acting upon
the object, and inversely upon the mass of the
object.
As the force acting upon an object is increased,
the acceleration of the object is increased. As
the mass of an object is increased, the
acceleration of the object is decreased.
Consider a man pushing a pick up
truck.
Increased Force
As the force acting upon an object is increased, the acceleration
of the object is increased.
Increased Mass
As the mass of an object is increased, the acceleration of the object is decreased.
Newton's second law of motion can be
formally stated as follows:
The acceleration of an object as produced by a
net force is directly proportional to the
magnitude of the net force, in the same
direction as the net force, and inversely
proportional to the mass of the object.
The Second Law is concerned with relating acceleration to
mass and net force.
Newton's second law of motion explains how an object
will change velocity if it is pushed or pulled upon.
Firstly, this law states that if you do place a force on an
object, it will accelerate (change its velocity), and it will
change its velocity in the direction of the force. So, a force
aimed in a positive direction will create a positive change
in velocity (a positive acceleration). And a force aimed in a
negative direction will create a negative change in velocity
(a negative acceleration).
Newton's First Law (Law of Inertia)
Newton's first law in everyday terms:
An object at rest will stay at rest, forever, as
long as nothing pushes or pulls on it. An
object in motion will stay in motion, traveling
in a straight line, forever, until something
pushes or pulls on it.
The "forever" part is difficult to swallow sometimes.
However, it is easy to imagine that an object at rest will remain at
rest forever, until pushed or pulled by something.
Now, just take that same idea and apply it to an object in motion.
But imagine that you have three ramps set up as shown below. Also imagine that
the ramps are infinitely long and infinitely smooth. You let a marble roll down
the first ramp, which is set at a slight incline. The marble speeds up on its way
down the ramp. Now, you give a gentle push to the marble going uphill on the
second ramp. It slows down as it goes up. Finally, you push a marble on a surface
that is perfectly horizontal. In this case, the marble will neither slow down nor
speed up. In fact, it should keep rolling. Forever.
According to Newton's first
law, the marble on that
bottom ramp should just
keep going. And going.
Physicists use the term inertia to describe this tendency of an object to
resist a change in its motion. The Latin root for inertia is the same root for
"inert," which means lacking the ability to move. So you can see how
scientists came up with the word. What's more amazing is that they came
up with the concept. Inertia isn't an immediately apparent physical
property, such as length or volume. It is, however, related to an object's
mass. To understand how, consider the sumo wrestler and the boy shown
below.
Which person in this ring will be harder to
move? The sumo wrestler or the little boy?
Let's say the wrestler on the left has a mass of 136 kilograms,
and the boy on the right has a mass of 30 kilograms (scientists
measure mass in kilograms). Remember the object of sumo
wrestling is to move your opponent from his position. Which
person in our example would be easier to move?
Common sense tells you that the boy would be easier to move,
or less resistant to inertia.
You experience inertia in a moving car all the time. In fact, seatbelts
exist in cars specifically to counteract the effects of inertia. Imagine for
a moment that a car at a test track is traveling at a speed of 55 mph.
Now imagine that a crash test dummy is inside that car, riding in the
front seat. If the car slams into a wall, the dummy flies forward into the
dashboard. Why? Because, according to Newton's first law, an object
in motion will remain in motion until an outside force acts on it. When
the car hits the wall, the dummy keeps moving in a straight line and at
a constant speed until the dashboard applies a force. Seatbelts hold
dummies (and passengers) down, protecting them from their own
inertia.
Newton’s Laws
1st Law Inertia
2nd Law F=ma
3rd Law Action/Reaction
Newton's 3 Laws