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Inertia vs. Momentum: What's the Difference?

Edited by Aimie Carlson || By Harlon Moss || Published on December 21, 2023
Inertia is an object's resistance to changes in motion, while momentum is the product of an object's mass and velocity, representing its motion.

Key Differences

Inertia is a property of matter that causes it to resist changes in its state of motion. Momentum, on the other hand, is a measure of the quantity of motion an object has, dependent on both its mass and velocity.
The concept of inertia is inherently tied to an object's mass, the greater the mass, the greater the inertia. Momentum differs as it combines both mass and velocity, meaning an object can have high momentum with either high mass, high velocity, or both.
Inertia is solely a function of mass and does not consider the direction or speed of an object. Momentum is a vector quantity, meaning it has both magnitude and direction, directly influenced by the object's velocity.
Inertia is what keeps a stationary object at rest or a moving object in motion at a constant velocity. Momentum, in contrast, quantifies the amount of motion an object has and is conserved in closed systems unless acted upon by external forces.
The role of inertia is often observed when attempting to start or stop an object's motion. Momentum becomes crucial in understanding the effects of collisions and the transfer of motion from one object to another.

Comparison Chart


Resistance to change in motion
Product of mass and velocity


Dependent on mass
Dependent on mass and velocity

Quantity Type

Scalar (no direction)
Vector (has direction)

Role in Motion

Maintains current state of motion
Represents amount of motion

Influence in Physics

Fundamental in Newton's First Law
Crucial in understanding collisions

Inertia and Momentum Definitions


Property keeping an object stationary or moving uniformly.
The car kept moving even after the engine was turned off, due to inertia.


Mass in motion.
The moving train had significant momentum, making it hard to stop quickly.


Inherent resistance to changes in velocity.
A satellite in space continues in its path due to inertia.


Quantity of motion of a moving body.
The momentum of the sprinter was evident in her swift acceleration.


Resistance to change in motion.
A heavy ball at rest shows inertia, resisting the push to move.


A conserved quantity in physics, indicating motion preservation.
In a car collision, momentum is transferred from one vehicle to another.


Measure of an object's resistance to acceleration.
It takes more force to accelerate a truck than a bike, demonstrating greater inertia.


Product of an object's mass and velocity.
A small bullet can have high momentum if it's moving fast.


The tendency to do nothing or remain unchanged.
The inertia of the system prevented any reforms.


Vector quantity representing motion's direction and magnitude.
The momentum of the thrown ball was directed upwards and outwards.


(Physics) The tendency of a body at rest to remain at rest or of a body in straight line motion to stay in motion in a straight line unless acted on by an outside force; the resistance of a body to changes in momentum.


Symbol p(Physics) A quantity used to measure the motion of a body, equal to the product of the body's mass and its velocity. Also called linear momentum.


Resistance or disinclination to motion, action, or change
An entrenched bureaucracy's inertia.


The force or energy exhibited by a moving body
The ball did not have enough momentum to reach the goalposts.


The property of a body that resists any change to its uniform motion; equivalent to its mass.


The driving force or advancing strength of a development or course of events
The effort to reform public education has been gaining momentum.


(figuratively) In a person, unwillingness to take action.


(Philosophy) An essential or constituent element; a moment.


(medicine) Lack of activity; sluggishness; said especially of the uterus, when, in labour, its contractions have nearly or wholly ceased.


(physics) Of a body in motion: the tendency of a body to maintain its inertial motion; the product of its mass and velocity, or the vector sum of the products of its masses and velocities.


That property of matter by which it tends when at rest to remain so, and when in motion to continue in motion, and in the same straight line or direction, unless acted on by some external force; - sometimes called vis inertiæ. The inertia of a body is proportional to its mass.


The impetus, either of a body in motion, or of an idea or course of events; a moment.


Inertness; indisposition to motion, exertion, or action; lack of energy; sluggishness.
Men . . . have immense irresolution and inertia.


The quantity of motion in a moving body, being always proportioned to the quantity of matter multiplied by the velocity; impetus.


Lack of activity; sluggishness; - said especially of the uterus, when, in labor, its contractions have nearly or wholly ceased.


Essential element, or constituent element.
I shall state the several momenta of the distinction in separate propositions.


A disposition to remain inactive or inert;
He had to overcome his inertia and get back to work


A property of an activity or course of events, viewed as analogous to forward motion or to physical momentum (def. 1), such that the activity is believed to be able to continue moving forward without further application of force or effort; - often used to describe an increase in the acquisition of public support for a purpose; as, as, the petition drive gained momentum when it was mentioned in the newspapers.


(physics) the tendency of a body to maintain is state of rest or uniform motion unless acted upon by an external force


An impelling force or strength;
The car's momentum carried it off the road


The product of a body's mass and its velocity;
The momentum of the particles was deduced from meteoritic velocities


How does mass affect inertia?

Greater mass increases inertia.

Is momentum scalar or vector?

Vector, as it has both magnitude and direction.

Is inertia a scalar or vector quantity?

Scalar, as it has magnitude but no direction.

What is momentum?

Mass in motion, quantified as the product of mass and velocity.

How does velocity affect momentum?

Higher velocity increases momentum.

How does inertia relate to Newton's laws?

It's central to Newton's First Law of Motion.

Why is momentum important in physics?

It helps explain the behavior of objects in motion, especially in collisions.

What is inertia?

Resistance of an object to change its state of motion.

What's an example of inertia in daily life?

A book remaining stationary on a table.

Can momentum change in an object?

Yes, with changes in velocity or mass.

Does inertia depend on speed?

No, it's independent of speed.

How is momentum conserved in a closed system?

The total momentum remains constant unless acted upon by external forces.

What happens to momentum if an object accelerates?

It increases as velocity increases.

What's a real-life example of momentum?

A moving car has momentum, making it difficult to stop quickly.

Can inertia change in an object?

Only if its mass changes.

What role does inertia play in a car crash?

It causes occupants to continue moving forward when a car suddenly stops.

How does momentum play a role in sports?

It affects how balls move and how athletes control their movements.

How do seat belts work in terms of inertia?

They counteract inertia by holding occupants in place.

What happens to inertia if an object accelerates?

It remains constant as it's independent of velocity.

Does momentum depend on speed?

Yes, it directly depends on speed.
About Author
Written by
Harlon Moss
Harlon is a seasoned quality moderator and accomplished content writer for Difference Wiki. An alumnus of the prestigious University of California, he earned his degree in Computer Science. Leveraging his academic background, Harlon brings a meticulous and informed perspective to his work, ensuring content accuracy and excellence.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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