Newton’s First Law of Motion: Law of Inertia
Inertia is a property of matter to resist change in its state of rest or uniform motion.
All matter has inertia.
The amount of inertia a body possesses depends on its mass.
Newton’s first law of motion says that a body at rest or in uniform motion will remain in that state provided that the net force acting on it is zero.
The law of inertia, which states that a body at rest remains at rest or a body in uniform motion moves in the same direction and at the same speed unless an external unbalanced force acts on it.
-----------------------------------------------------------------------
Newton’s Second Law of Motion: Law of Acceleration
Newton’s second law states that the acceleration of an object is directly proportional to and in the same direction as, the net force and is inversely proportional to the mass.
Force is that which causes a body to move or to accelerate.
One Newton of force is equal to 1X 10^5 dyne.
-----------------------------------------------------------------------
Sample Problem 1
A car with a mass of 3,000kg is accelerated from rest at the rate of 5 m/s2. What is the net force applied on it?
------F= ma-----------= (3,000kg)(5m/s^2)-----= 15,000kg m/s^2
------------------------------------------------------------or 15,000N
-----------------------------------------------------------------------
Sample Problem 2
A force 20N is applied to a 5 kg block that is at rest on a level surface. Find the acceleration produced, the velocity of the block after 6 seconds, and lastly the distance it has gone after 6 seconds.
* the acceleration produced
------a = F/m---------= 20N/5kg----------------= 4m/s^2
*the velocity of the block after 6 seconds
------V= at------------= (4m/s^2)(6s)-----------= 24m/s
*the distance it has gone after 6 seconds
------d = ½ at^2 ----= ½(4m/s^2)(6s)^2 -----= 3m
-----------------------------------------------------------------------
Sample Problem 3
What is the mass of an object accelerated to 6 m/s2 by a force of 18N?
------m= F/a --------= 18N/6m/s^2 ------------= 3kg
-----------------------------------------------------------------------
Sample Problem 4
A 2000kg car decelerates from 10m/s to 5 m/s in two seconds. Find the force acting on it.
------a =V2-V1------= 5m/s – 10m/s------------= -2.5 m/s^2
------------t------------------2s
------F = ma --------= (2000kg)(-2.5m/s^2)---= 5,000kgm/s^2 or
------------------------------------------------------------5,000 N
-----------------------------------------------------------------------
Newton’s Third Law of Motion: Law of Interaction
Newton’s second law states that for every action force there is always an opposite and equal reaction force.
Force does not cancel out each other.
Forces act in pair.
