Subsection 2.2.2 Newton’s Laws of Motion
Newton recognized that there are two kinds of motion, uniform motion and accelerated motion. Uniform motion: the movement of an object traveling in a straight line at a constant speed (no acceleration). Accelerated motion: the movement of an object traveling under the influence of some source of acceleration. On that basis he defined three laws of motion called Newton’s laws of motion.
-
Newton’s first law is the definition of a force which states that every object in a state of rest remains at rest or in a state of uniform motion tends to remain in uniform motion along the same direction, unless an external force is applied to it. Force is not required to continue the motion of anything which is already in motion. The first law is also called a law of inertia. Inertia is an ability of an object to resist any changes in its motion. Mass is related to inertia, the bigger the mass the more difficult it is to change the state of rest or motion of an object. Mass: It is the amount of matter contained in an object. It is also reposible for the force of gravity of the object.Some examples of I law: 1. When the bus driver abruptly applies the breaks, passengers tend to feel a momentary pull in the forward direction. The reason behind this jerk felt by the passengers sitting inside the bus is the law of inertia. Due to inertia, our upper body part continues to maintain a state of motion even after the bus stops, thereby pushing us in the forward direction. 2. A book kept on a bookshelf does not change its shape, size, or position until acted upon by an external force. 3. A runner is not able to stop himself right after crossing the finish line. He/She tends to take time and cover a few meters of distance running beyond the finish line. This is because the inertia of motion resists a sudden termination of motion and compels the body to maintain its state of motion.
- Newton’s second law is the measurement of a force which states that the acceleration of the object is directly proportional to the applied force and takes the direction of that force. Newton’s II law can be expressed as\begin{equation} F=ma\text{.}\tag{2.2.3} \end{equation}Where \(m\) is the mass of the object.
-
Newton’s third law is the property of force which states that for every action there is an equal and opposite reaction. Force always comes in pair. If an object A applies the action force on the object B then object B also applies the same amount of reaction force on the object A. These forces pair always act on two different objects. If one object exerts a force on a second object, then the second object exerts an equal but oppositely directed force on the first object. Mathematically,\begin{equation} F_{AB}=-F_{BA}.\tag{2.2.4} \end{equation}Some examples: 1. Earth exerts force on you because you exert an equal and opposite force on earth. Here your force is your body weight and earth reaction force is a normal force. 2. When the rifle is fired it exerts a force on the bullet and the bullet exerts an equal and opposite force on the rifle. 3. You are able to sweem in water because you pushes water backwardly so apply the force on water and in reaction water also applies the same force on you just in opposite direction so you can sweem nicely.
