Newton’s Laws of Motion What is Newton's First Law? When an object is at rest, it does not have any motion unless an external force is exerted. On the other hand, if an object is pushed to slide on the floor and if we stop pushing it, we observe that it will stop in a determined instant. This is called Newton’s First Law of Motion. Newton's First Law of Motion states that an object in motion tends to stay in motion unless an external force acts upon it. Similarly, if the object is at rest, it will remain at rest unless an unbalanced force acts upon it. Newton's First Law of Motion is also known as the Law of Inertia. The idea that objects only change their velocity due to a force is encapsulated in Newton's first law. Newton's first law: An object at rest remains at rest, or if in motion, remains in motion at a constant velocity unless acted on by a net external force.
The EXTERNAL FORCE can be the resultant of two or more forces exerted on the same object. When an object is at rest or in motion and if a change of state is required, it will have some resistance. This property that all objects have to resist the change in motion is known as INERTIA. We can appreciate that for a greater mass, the inertia of the object (its resistance to the change in motion) is greater and vice versa, for an object with less mass its resistance to the change in motion will be less. We conclude that mass is a quantitative measure of inertia. This property is characteristic of all matter.
What is Newton's Second Law? Newton's Second Law of Motion states that when a force acts on an object, it will cause the object to accelerate. It expresses what happens to a body when it is not in equilibrium, this is, when on it acts a resultant force different from zero. Newton’s Second Law refers to the changes in speed of an object, when a resultant force is exerted, it is not null and it produces an acceleration. The acceleration of an object has presence not only in the change of magnitude, but also in the change of direction caused by the velocity or both. Newton’s Second Law states that when a body is not in equilibrium there is a change in its velocity, this is, the body is accelerated. By the other hand, its describes the relation between the acceleration produced, the applied force and the mass of the body. Newton’s second law: All resultant force exerted on an object, will produce an acceleration in the same direction which is exerted. The magnitude of such acceleration is directly proportional to the magnitude of the exerted force and inversely proportional to the mass of the object. This is the classical expression of Newton’s second law: If the exerted force on a mass is equal to zero, the acceleration will also be zero and there is no change in motion. This is, if the mass is at rest, it will remain at rest and if it is in motion it will remain in constant motion, as it is predicted in Newton’s First Law of Motion. In the application of the classical expression of the Newton’s second law there are some limitations because this law cannot be used in light speed, nor in the study of the behavior of particles and atoms. The acceleration of an object has always the direction of the exerted resultant force. If the force is exerted opposite to the motion’s direction, the velocity will decrease and the acceleration will be negative. If the force exerted forms an angle with same motion’s direction,
The acceleration of an object depends on the force exerted on the object and on its mass, and not on the type of force (gravitational, electric, magnetic, etc.). The larger the mass of the object, the greater the force will need to be to cause it to accelerate. This Law may be written as force = mass x acceleration or: F = m * a Another way to state the Second Law is to say it takes more force to move a heavy object than it does to move a light object. The law also explains deceleration or slowing down. You can think of deceleration as acceleration with a negative sign on it. We know objects can only accelerate if there are forces on the object. Newton's second law tells us exactly how much an object will accelerate for a given net force.
What is Newton's Third Law? Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. What this means is that pushing on an object causes that object to push back against you, the exact same amount, but in the opposite direction. Newton's third law: If an object A exerts a force on object B, then object B must exert a force of equal magnitude and opposite direction back on object A (For every action, there is a reaction force that is equal in size but opposite in direction).
This law represents a certain symmetry in nature: forces always occur in pairs, and one body cannot exert a force on another without experiencing a force itself. We sometimes refer to this law loosely as action-reaction, where the force exerted is the action and the force experienced as a consequence is the reaction.