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Essence of Newton’s Laws of Motion

Since inception, Newton’s laws have been used in literally all spheres of physics. The laws have been applied in diverse fields to generate solutions to many a problem. This paper provides a detailed research, and an in depth review of Newton’s first, second and third laws of motion.

Newton’s laws of motions form a fundamental element of physical science pertaining movement of bodies, and their ability to remain in motionless state. The laws describe the different elements that initiate and control motion of objects within the surface of the earth (Gianopoulos, 2007).

Before the development of these laws of motion, and during the antiquity era, philosophers extensively employed the concepts of force to study stationary and objects in motion, in simple machines. The understanding of force during the period remained limited owing to the assumption of non-obvious forces that offered resistance to motion like friction, among others. Among the fundamental errors of the period was the notion that moving objects required force to maintain constant velocity.

Majority of the misunderstandings presented during the early periods became crystal clear following the invention of the laws of motion by Isaac Newton. These laws presented scientists with an insightful understanding of the various elements affecting motion of objects (Stronge, 2004). These laws remain fundamental to the understanding of motion in totality. The laws could be summarized by the following three statements.

  • The velocity of a moving object remains constant unless the object is acted upon by an external force.
  • The acceleration (a) of a body is directly proportional to the force (F) applied and inversely proportional to the body mass (m) i.e., F=ma
  • The forces of two bodies on each other are always equal, and are directed in opposite directions.

The above three statements form the first, second, and third Newton’s laws of motion respectively.

Force and Motion

Force refers to the physical influence that causes observable or measurable change in objects either through geographical construction or movement. Any influence that could initiate measurable change within an object containing mass could essentially be termed as force. The impact of force on an object occurs in both magnitude and direction, meaning that force remains an element of vector in science (Kirkland, 2007).

The force applied upon a stationary object initiates a movement that results into motion of the specified object. Newton’s laws of motion offer a deep explanation of the relationship existing between the force and motion. Since motion involves movement, the quantification of motion remains expressed in terms of acceleration and velocity.

The first law describes the influence of force on the motion of an object. Within the context of this law, motion becomes expressed in terms of the velocity of the object under discussion, and the law states that the velocity would remain constant upon non-application of any external force(s). This law would imply that force can change the motion of an object either in magnitude or direction.

The second law of motion further explains these two fundamental elements of movement through offering a relationship between these elements. Within the context of this law, the acceleration of the object remains represents the motion (Beatty, 2006). The law presents a clear relationship between the elements through the equation explaining that the two elements remain directly proportional to each other. The second law introduces a constant in the mass of a specified object upon which force becomes applied.

Newton’s third law of motion disputes the notion of unidirectional force, by indicating that forces existing in bodies act in numerous directions. The law ascertains that whenever a body exerts force upon another, the other body exerts an equal amount of force. This law could sometimes be referred as the action-reaction law owing to the forces acting in opposite directions to neutralize each other. Force within the context of the third law could be expressed in terms of pushes and pulls.

An object that remains stationary could offer a clear explanation of this law of motion. The object below remains stationary on the surface. F1 presents the action force exerted on the surface by the object while F2 presents the reaction force offered by the surface. If the forces do not equal each other, the object would move in the direction with little force. The action and reaction forces cause objects to remain in a motionless state, unless one force exceeds the other.

Force and Motion

Motion and Inertia

In physical science, motion could be defined as the change in position of an object with time. Naturally, motion could be described in different forms related to time, velocity, acceleration, and displacement. The measurement of this physical element of science requires the attachment of a reference point for the object, whose motion should be measured. Under normal circumstances, the motion of an object could only be instigated by forces acting upon the specified object.

Bodies showing no change in their position could be described as motionless owing to the ability to remain in the same position with time. The application of force onto a motionless body initiates motion into the body, and the forces that initiate motion could be identified as the motion forces.

While some forces initiate motion in motionless objects, there exist other forces that tend to resist the motion of the specified object. Inertia, on the other hand, could be used to describe the forces that offer resistance to motion of stagnant bodies (Serway & Faughn, 2006). The term inertia comes from the Latin word iners, which means idle.

Inertia can, therefore, be defined as the tendency for bodies to resist change of initiated motion. The principle of inertia, therefore, forms a fundamental part of classical physics, used in describing the motion of substances and the effects of forces acting upon the substances. The most common forms of inertia motions within the earth’s surface remain to be friction and gravity. The two forms tend to decrease the speeds of moving bodies.

Newton’s first law of motion immensely involves motion and inertia as two opposing forces to the movement of motionless objects. The first law of motion states that “The velocity of a body remains constant unless the body is acted upon by an external force”. The velocity of a body within the context of the first law of motion refers to the motion initiated upon the body.

The external force supposed to change the velocity can be identified as the inertia forces resisting motion of the specified object. The close relation of Newton’s first law to motion and inertia contributes immensely to the law being referred to as the law of inertia (Zimba, 2009). According to this law an object would remain in a state of inertia unless acted upon by some external force. Similarly, an object moving on a flat surface would maintain a constant velocity, unless acted upon by some inertia force to reduce the velocity.

The second law of motion identifies acceleration as being directly proportional to the force applied upon the object. This directly implies that an increase in the force could automatically result into an increase in the acceleration of the object under discussion. Inertia forces, like friction, tend to offer resistance to the force causing the motion, hence reducing the influence of the forces upon the specified object.

Newton’s third law of motion offers an explanation of the inertial state of stationary objects by introducing the action and reaction forces. When the forces of action and reaction become equal, an object remains bound to stay in the state of inertia until one force exceeds the other (Thornton, 2004).

If the surface described in fig. 1 above tilts, the reaction force (F2) would reduce significantly, and instigate motion upon the object. During the inertia state, the two forces could be described as equaling each other hence creation a balance between the object and the surface. The state of inertia can essentially be described as the equilibrium between two opposing forces.

Mass and Weight

Mass and weight remain two constantly confused elements of measurement within the context of average livelihood. While the elements remain closely related, they also remain different in terms of concept and quantity. Mass could essentially be defined as the amount of matter within an object. Weight, however, refers to the force exerted by the object upon the earth’s surface. The mass of an object remains constant as mass remains an independent constant of measurement.

Weight, however, remains an element of gravitational force and could change when the gravitational force changes. The weight of any object remains a function of the gravitational force, while mass remains constant to any observer.

The weight of an object can be expressed by multiplying the mass by the gravitational field strength at a given position within the earth’s surface. The unit for measuring masses of objects remains kilogram (kg), newtons represent the weight of objects as newton remains the unit of measuring force. Being a function of force, the unit for expressing weight becomes the same as that of expressing force (the newton). Weight could essentially be described as the force exerted by a mass on the earth’s surface, quantified in newtons.

The Newton’s laws of motion explain the differing values of weight achieved from measuring similar mass under different conditions (Galili & Tseitlin, 2003). The weight of an inflated balloon on a weighing scale could become immensely faulty owing to the impacts of buoyancy. Buoyancy can be defined as the resistance offered by fluids on masses placed in fluids.

The effects of buoyancy cause immense reduction in the weight of a mass when placed within a fluid. When measuring weights of objects placed in fluids, the weight of the objects becomes partially transferred to the fluid depending on the fluid under discussion. Fluids tend to offer resistance to gravitational force, and could overcome the gravitational strength completely.

In the case of a balloon floating in the air, the gravitational pull becomes overcome by the buoyancy of the fluid hence the balloon moves up. This situation supports the statement of the third law of motion. Forces resisting the gravitational pull overcome its force causing the balloon to move in the direction of those forces. The direction of balloon becomes controlled by the direction of the fluid initiating the buoyancy.

Equal and Opposite Forces

Equal and opposite forces refer to the forces that act in opposing directions of each other. Individuals, however, tend to confuse the action of these forces as stipulated by Newton’s third law of motion. The law does not refer to two forces acting on a single object, rather, forces acting on different objects.

A book lying on a table, for example, experiences equal and opposite forces (Kirkland, 2007). The book experiences a downward force exerted by the earth, and an upward force exerted by the table. Newton’s third law identifies these two, forces acting in opposite directions, on different objects. The first force, exerted by the earth, acts on the table, and the second force, exerted by the table, acts on the book.

According to the first and second laws, for the book to remain stationary, the forces must be equal. The above mentioned forces present a clear indication of opposite and equal forces acting on two objects. These forces help to maintain the state of the object on the surface until another force becomes present on the object. This situation could essentially be termed as a balance between forces that assists in maintaining present object state.

Were the table to be tilted, the forces would cease to be equal and opposite. The confusion of these equal and opposite forces occurs when the third law becomes abbreviated and stated as “for every action, there is an equal and opposite reaction” (Galili & Tseitlin, 2003, p. 49). This abbreviation of the third law remains the misleading point for a majority of physics scholars. This abbreviation fails to point out that the forces normally act on different objects.

Equilibrium

The position of equilibrium could be used to describe the position at which a balance between two opposing forces can be achieved. In layman’s terms, equilibrium can be achieved at the point where a balance between the opposing forces can be reached. This point means that the two forces equal each other, thus they achieve a balance upon the object in which the forces act. At equilibrium, all forces acting on an object must equal to zero. According to Newton’s laws of motion, when all the forces acting on a single object become zero, a state of mechanical equilibrium becomes achieved.

Rigid objects could achieve mechanical equilibrium when they do not undergo any acceleration internally or externally. When the forces exerted on an object from different directions become equal, an equilibrium state could also be achieved. At equilibrium objects appear to display a balance in the stationary state with no signs of acceleration (Beatty, 2006).

Stationary objects, however, experience a different kind of equilibrium called static equilibrium, owing to the lack of motion. The state of equilibrium could be achieved when a force resisting motion equals the force initiating the same motion. According to the third law of motion, this would be achieved through the equal and opposite forces. At the point where these forces become equal, and balance becomes achieved, an equilibrium state naturally occurs.

References

Beatty, M. F. (2006). Principles of Engineering Mechanics: Dynamics-The Analysis of Motion. London/Berlin: Springer.

Galili, I. & Tseitlin, M. (2003). Newton’s First Law: Text, Translations, Interpretations and Physics Education. Science & Education, 12 (1), 45–73.

Gianopoulos, A. (2007). Isaac Newton and the Laws of Motion. Minnesota: Capstone Press.

Kirkland, K. (2007). Force and Motion. New York: Infobase Publishing.

Serway, R. A. & Faughn, J. S. (2006). College Physics. Pacific Grove CA: Thompson-Brooks/Cole.

Stronge, W. (2004). Impact mechanics. Cambridge UK: Cambridge University Press.

Thornton, M. (2004). Classical dynamics of particles and systems (5th ed.). Pacific Grove CA: Brooks/Cole.

Zimba, J. (2009). Force and Motion: An Illustrated Guide to Newton’s Laws. Baltimore, Maryland: Johns Hopkins University Press.