# Newton's Laws of Motion

#### Academic Questions in PhysicsPlease check out our Test Your Knowledge page to see all Questions and Answers The rate of change of momentum is proportional to the applied force and will take place in the direction of that force. The above statement is attributed to _____. A. Albert Einstein B. Isaac Newton C. Galileo Galilei D. Neils Bohr E. Ernest Rutherford F. Marie Curie The Law of Inertia is also referred to as _____. A. 1st Law of Thermodynamics B. 2nd Law of Thermodynamics C. 3rd Law of Thermodynamics D. Newton's 1st Law of Motion E. Newton's 2nd Law of Motion F. Newton's 3rd Law of Motion The process whereby the velocity of an object increases and decreases over a period of time is best associated with the term _____. A. Speed B. Velocity C. Momentum D. Constant Velocity E. Acceleration F. Average Velocity The rate of motion is best referred to as _____. A. Speed B. Velocity C. Momentum D. Inertia E. Acceleration F. Constant Velocity 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 ### Newton's Laws of Motion:

Motion can be defined as a change in the position of an object with reference to time.

We have 3 laws of motion as postulated by Sir Isaac Newton in 1687. These are:

1. Newton's First Law of Motion

2. Newton's Second Law of Motion

3. Newton's Third Law of Motion

Note: A good knowledge on the concept of force will aid you to better understand the above laws.

• #### Newton’s First Law of Motion

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

An object at rest 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.

The concept of inertia implies that an object at rest will continue at rest while another in uniform motion will keep moving in a straight line.

Note: Think of inertia as being resistant to change.

Inertia is a property of matter.

It was Newton’s first law of motion that shows the presence of inertia in a body at rest (or in a body moving with 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.

In conclusion, the Law of inertia which is a reference to Newton’s first law of motion summarizes what force can do (in relation to mass).

• #### 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

Newton's Third Law of Motion states that action and reaction are equal and opposite.

The third law can also be stated thus:

To every action, there is an equal and opposite reaction

Consider the instance below:

When a boxer blows a wall, he will in return feel a reverse force on his hands.

Although the boxer exerts a force on the wall (in the above instance), the wall in return actually exerts an opposite force on hands of the boxer. Based on this fact, the boxer may feel some pain on his hands depending on the nature of the wall and the degree of force exerted on 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.

According to the Third Law of Motion; if a body A exerts a force FA on another body B, the body B will in return exert an equal and opposite force FB back on body A. The forces FA and FB are therefore 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 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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