Force and Motion - Newton's Laws of Motion

len Alfred Ajibola - Thu, 11th July, 2019 @ 15:00: PM

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Academic Questions in Physics

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Consider this expression below:

A body X exerts a force FX on another body Y. In return, body Y exert a force FY back on body X. The forces FX and FY are equal in magnitude but opposite in direction.

Putting the above expression into equation:

FX = -FY

Where FX is the action force

FY is the reaction Force

The above expression relates to _____.

  • A. Theory of Force
  • B. Force Postulate
  • C. Einstein's proposal on Relativity
  • D. Newton's 1st law of motion
  • E. Newton's 2nd law of motion
  • F. Newton's 3rd law of motion

The tendency of a body to remain in a state of rest or in uniform motion is referred to as _____.

  • A. tension
  • B. uniform acceleration
  • C. constant acceleration
  • D. deceleration
  • E. inertia
  • F. velocity

A change in the position of an object with reference to time is best described as _____.

  • A. momentum
  • B. displacement
  • C. velocity
  • D. acceleration
  • E. direction
  • F. motion

The saying "what goes up on earth must come down" can be best attributed to _____.

  • A. force
  • B. motion
  • C. mass
  • D. acceleration
  • E. average velocity
  • F. constant velocity

We have _____ laws of Thermodynamics.

  • A. 1
  • B. 2
  • C. 3
  • D. 4
  • E. 5
  • D. 6

Which Scientist successfully discovered the theory of special relativity?

  • A. Albert Einstein
  • B. Isaac Newton
  • C. Galileo Galilei
  • D. Neils Bohr
  • E. Ernest Rutherford
  • F. Marie Curie

The scientific study of matter and the movement of matter through space and time is a concept of _____.

  • A. Biology
  • B. Chemistry
  • C. Physics
  • D. Basic Science
  • E. Geography
  • F. Physiology

10oF is associated with _____.

  1. temperature
  2. pressure
  3. atmospheric pressure
  4. rainfall
  5. direction of wind
  6. speed of wind


Sir Isaac Newton presented the laws of motion (which will later be accredited to his name) in 1968. These motion laws of Newton gives us the relationship between the forces acting on a body and the motion of the body.

Recall that motion refers to a change in the position of an object with reference to time.

You can please read on motion here

When a body is at rest, let say a pen resting on a table; the pen will continue to remain on the table unless it is pushed or pulled by something. This push or pull with the tendency of making the pen move away from its exact position is known as force.

Note: Force exists as a result of an interaction between two objects. From the above instance, if nothing interacted with the pen on the table, then the pen will continually remain on the table. If there is no interaction between objects, force will never be experienced.


Introduction to Force

Force is a vector quantity because it has both magnitude and direction. Any form of push or pull acting on an object is termed force. You probably may have heard an adage that states thus: “what goes up must come down”.

This is true because the earth in itself has a force acting on it. This force, called the gravitational force of the earth acts by pulling all things towards the earth. In order to move away from the earth, there must be another constant force greater than the gravitational force or force of gravity. It is this applied force in aeroplanes and jets, against gravitational force that makes them move away (fly) from the earth.

In another instance, when you jump, you apply a force; but since this applied force isn’t constant, the force of gravity present on earth eventually bring you back down. Please read on the amazing facts of gravity here.

Note: Force as a quantity is measured in Newtons (N), in honor of Sir Isaac Newton for the great work he has done. Force can be balanced or unbalanced. To summarize this;

An apple hanging on a tree has a balanced force.

An apple falling from a tree has an unbalanced force.

With our explanation on force and motion, we can now understand more easily; the Newton's laws of Motion.


  • Newton’s First Law of Motion

Also known as Law of Inertia, Newton’s First Law of Motion states that:

An object will continue to stay in its state of rest or if the object is in uniform motion, it will continue to move in a straight line UNLESS an external force acts on it.

When no force is applied to a body, the tendency or outcome of the body to remain in a state of rest or in a uniform linear motion is known as Inertia. This imply that with inertia, an object at rest will continue at rest while another in a straight line motion will keep moving of the straight line. "Think of inertia as being resistant to change"

Inertia is a property of matter. It is Newton’s first law of motion that shows the presence of inertia in a body at rest or in another moving in a constant velocity.

Note: Matter is anything that has mass and occupy space. Mass is a measure of inertia; thus the bigger the mass of an object, the more inertia the object would have. Please read on matter here.

In conclusion of the law of inertia, Newton’s first law of motion summarizes what force can do.


  • Newton’s Second Law of Motion

Newton’s second law of motion states that the rate of change of momentum is proportional to the applied force and will take place in the direction of that force.

Think of momentum as mass in motion; that is, the quantity of motion a moving body has. Momentum is the product of mass and velocity. You may have heard the commentator of a football match commenting that “a team has gained momentum”. This will simply imply that the team is on the move or pressing high.

When we apply the second law of motion to reality, it will help us determine the amount of force needed to make an object move or stop. This second law is applied in various field of sports including football, basketball and cricket. In the game of cricket for instance, the players will usually pull back their hands when catching the ball. This is so because “pulling back the hands” increases the time of contact with the ball thus resulting in less jerk from the motion of the caught ball.

Note: Through Newton’s second law of motion, we are able to define an absolute unit of force which remains constant under a moving condition. Also, the second law of motion gives us the operational definition of force as the rate of change of momentum with time.


  • Newton’s Third Law of Motion

It states that action and reaction are equal and opposite.

The second law can also be stated thus:

To every action, there is an equal and opposite reaction

Consider this instance, when a boxer blows a wall, he will in return feel a reverse force on his hands. Even though this boxer exerts a force on the wall, the wall in return will exert an opposite force on hands of the boxer. The boxer may feel some pain on his hands based on the nature of the wall and the reverse force from the wall.

Note: Playing football without boots might get you injured when you kick a player. This is so because there is a reverse force from the kicked player. Newton’s third law exist almost on everything that has mass. It is also often seen and encountered in a wrestling match.

Finally, the third law imply that when a body A exerts a force FA on another body B. In return, body B will exert a force FB back on body A. The forces FA and FB are equal in magnitude but opposite in direction.

We can therefore write the above expression as

FA = -FB

Where FA is the action force

FB is the reaction Force

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Alfred Ajibola is a Medical Biochemist, a passionate Academician with over 7 years of experience, a Versatile Writer, a Web Developer, a Cisco Certified Network Associate and a Cisco CyberOps Associate.

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