Force and motion. Newton’s three laws of motion

21/04/2026

The online force and motion simulations on this page will help you understand how forces generate motion and how they modify it in magnitude and direction. We will review Newton’s three laws of motion, which are precisely the laws that govern the relationship between force and motion.

This Thematic Unit is part of our Physics collection

Acceleration

Change in the velocity vector of a body per unit of time as a result of a net force.

Applied Force

External force directly exerted on an object to modify its physical or motion state.

Dynamics

Part of mechanics that studies the relationship between the forces acting on a body and the effects they produce on its motion.

Friction Force

Force opposing motion that arises from the interaction between two surfaces in contact.

Interaction

Mutual action or reciprocal influence between two or more bodies resulting in the appearance of forces.

Mass

Amount of matter in a body, constant throughout the universe. The SI unit of measurement is the kilogram (kg) and in the English system the pound (lb).

Newton’s Second Law

Law stating that an object’s acceleration is directly proportional to the applied net force and inversely proportional to its mass.

Newton’s Third Law

Principle stating that if one body exerts a force on another, the latter responds with an equal and opposite force.

Relationship between force and motion

The physics of forces and motion is one of the most important branches of physics. It focuses on studying how objects move in response to forces acting on them.

Newton’s three laws of motion

Newton’s laws are three fundamental principles that describe the motion of objects in space and are the basis of classical physics. These laws are fundamental to the understanding of classical physics and apply in a wide variety of situations, from the motion of planets in space to the behavior of everyday objects on Earth.

Newton’s three laws of motion are::

First law. Law of inertia

Newton’s first law of motion, also known as the law of inertia,, states that an object at rest will remain at rest and an object in motion will continue to move with constant velocity in a straight line unless a net force acts on it.

Second law. Fundamental law of dynamics

Newton’s second law of motion, also known as the fundamental law of dynamics, states that the net force acting on an object is equal to its mass multiplied by its acceleration, that is, F = m x a. This means that the greater the force applied to an object, the greater its acceleration and the greater its mass, the harder it is to accelerate it.

Third law. Law of action and reaction

Newton’s third law of motion also known as the law of action and reaction, states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object exerts a force of equal magnitude and opposite direction on the first object.

Acceleration

Change in the velocity vector of a body per unit of time as a result of a net force.

Applied Force

External force directly exerted on an object to modify its physical or motion state.

Dynamics

Part of mechanics that studies the relationship between the forces acting on a body and the effects they produce on its motion.

Friction Force

Force opposing motion that arises from the interaction between two surfaces in contact.

Interaction

Mutual action or reciprocal influence between two or more bodies resulting in the appearance of forces.

Mass

Amount of matter in a body, constant throughout the universe. The SI unit of measurement is the kilogram (kg) and in the English system the pound (lb).

Newton’s Second Law

Law stating that an object’s acceleration is directly proportional to the applied net force and inversely proportional to its mass.

Newton’s Third Law

Principle stating that if one body exerts a force on another, the latter responds with an equal and opposite force.

Explore the exciting STEM world with our free, online, simulations and accompanying companion courses! With them you’ll be able to experience and learn hands-on. Take this opportunity to immerse yourself in virtual experiences while advancing your education – awaken your scientific curiosity and discover all that the STEM world has to offer!

Force an motion simulations

Races
Weight
Motion

Drag and push races

Watch these runs of two objects being dragged or pushed by a force and see what happens to the velocity and acceleration when the values of the applied force and the mass of the object are changed.

Drag by weight

Relationship between force and motion

Explore the forces that act when pulling a cart or pushing a refrigerator, box, or person. Create an applied force and see how it makes objects move. Change the friction and see how it affects the motion of objects.

Equation
Mass
Races
Weight
Motion

Analysis of the equation F=ma

This simulation visualizes the relationship between force, mass and acceleration.

Force in a constant mass

This simulation visualizes what happens to the acceleration and velocity when a force is applied to a constant mass.

Drag and push races

Watch these runs of two objects being dragged or pushed by a force and see what happens to the velocity and acceleration when the values of the applied force and the mass of the object are changed.

Drag by weight

Relationship between force and motion

Giants of science

“If I have seen further, it is by standing on the shoulders of giants”

Isaac Newton

Archimedes

287 a.C.

–

212 a.C.

Archimedes established fundamental principles of mechanics and hydrostatics, including the famous Archimedes’ principle of buoyancy in fluids

“Give me a place to stand, and I will move the world”

Leonhard Euler

1707

–

1783

Euler developed much of modern mathematical notation and made key contributions to analysis, topology, mechanics, and graph theory

“Nothing takes place in the universe without mathematics expressing it”

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Giants of science

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Isaac Newton

William Rowan Hamilton

1805

–

1865

William Rowan Hamilton developed Hamiltonian mechanics and quaternions, unifying geometry and mathematical physics

“Mathematics and physics meet in the harmony of the equations governing motion.”

Daniel Bernoulli

1700

–

1782

Daniel Bernoulli formulated Bernoulli’s principle and developed fundamental theories in fluid mechanics and gas dynamics

“Nature is always economical in its means”

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Test your knowledge

What is the relationship between forces and motion according to classical physics?

In classical physics, the relationship between forces and motion is described by Newton’s three laws of motion. The first law states that an object remains at rest or in uniform straight‑line motion unless a net force acts on it, introducing the concept of inertia. The second law explains how motion changes when a net force is present: acceleration is proportional to the applied force and inversely proportional to the object’s mass, expressed as F = m·a. The third law states that every action force has an equal and opposite reaction force. Together, these laws allow the analysis of everyday movements and astronomical phenomena, providing a mathematical framework to predict trajectories, accelerations and dynamic effects.

How are Newton’s three laws interpreted when analyzing an object’s motion?

Newton’s three laws provide a coherent framework for understanding how and why objects move. The first law describes behavior in the absence of net forces: an object does not change its state of motion without an external cause. The second law quantifies that cause, stating that the acceleration produced depends on both the applied force and the object’s mass. This makes it possible to calculate how motion evolves in real situations. The third law introduces the idea of interaction: forces always appear in pairs, explaining phenomena such as propulsion or recoil. Together, these laws allow the analysis of complex mechanical systems, from accelerating vehicles to falling objects or orbiting bodies.

Why doesn’t an object change its motion if no force acts on it?

An object does not change its motion because it has inertia, the tendency to keep its current state. If it is at rest, it stays still; if it moves in a straight line, it continues that way unless something pushes or pulls it. To change its speed or direction, a net force must appear. Without a force acting, there is no reason for the motion to change.

What does the equation F = m·a really mean in everyday life?

The equation F = m·a means that an object’s acceleration depends on the force applied to it and on its mass. In daily life, this explains why pushing a heavy object is harder than pushing a light one: the same force produces less acceleration. It also explains why a car accelerates faster when it carries little weight. The equation shows that changing an object’s motion requires a force proportional to the change you want to achieve.

What does it mean that every action has an equal and opposite reaction?

It means that when one object exerts a force on another, the second object responds with a force of the same magnitude but in the opposite direction. You can see this when walking: you push the ground backward and the ground pushes you forward. It also happens when a rocket expels gases downward and rises due to the reaction force. The forces do not occur one after the other; they appear simultaneously as part of the same interaction.