An Overview of Newton’s 3 Laws of Motion

By his early twenties, Sir Isaac Newton would publish his masterpiece in 1687: Philosophiæ Naturalis Principia Mathematica, which outlined his Laws of Motion. This groundbreaking work outlined his Laws of Motion and his Law of Universal Gravitation. It transformed the way humanity viewed nature and is a stepping stone in understanding physics.

The Laws of motion govern macroscopic bodies or objects and are foundational to classical mechanics (the study of the motion of objects). A good way to understand Newton’s Laws is by picturing or playing with Newton’s Cradle, a desk toy as seen in this text’s opening image.

Newton’s First Law: Inertia

His first law, also known as It is also known as the Laws of Inertia, states: “An object in motion will stay in motion, and an object at rest will remain at rest, unless acted upon by a force”. When you pull and go one of the balls in Newton’s Cradle, you’re hitting the other balls with a force, thereby a force is acting on an object at rest. And when you don’t hit the balls, nothing happens, or the object at rest stays at rest. Also, the reason that the balls don’t keep swinging forever is that there are a couple of other forces at play, namely air resistance and drag from the strings, the frame, and the balls themselves. The Law of Inertia why objects maintain their state of motion or rest without external forces.

Newton’s Second Law: F = ma

Forces are measured in newtons (N). One newton is the force needed to accelerate a 1-kilogram mass by 1 meter per second squared (1 N = 1 kg · m/s²). I could say in Newton’s Cradle, the force (F) hitting the balls is mathematically equal to the mass (m) of the ball you’re letting go multiplied by its acceleration (a). However, this wouldn’t be entirely true, as the force isn’t just from the ball you release but also from gravity and the collision itself. So, Newton’s second law predicts motion by calculating how force, mass, and acceleration interact.

Newton’s Third Law: Action-Reaction

Newton’s Third Law of Motion states that for every action, there is a mathematically equal and opposite reaction. In the example of the cradle, when you let go of the metal ball, there is an equal and opposite force acting on the other balls. Again, this force is subdued over time due to air resistance and drag. The third law is best for understanding how objects react to each other and can be used for things like bouncing a ball or launching a rocket.

Conclusion

These laws from about 300 years ago predict and describe motion relatively accurately, although most physicists use the Hamiltonian Laws of Motion and the Lagrangian Laws of Motion more often due to their accuracy, which builds on Newton’s. Newton’s Laws, however, are where anyone should start their physics education