Newton’s Laws of Motion are among the most important principles in physics, helping us understand how and why objects move. Whether it’s an airplane in flight or a ball falling to the ground, these laws explain the forces behind motion. In this guide, we’ll explore Newton’s First Law of Motion and Newton’s Second Law of Motion with easy examples and real-world applications.
What Are Newton’s Laws of Motion?
Sir Isaac Newton developed three fundamental laws that describe how objects behave when forces act upon them. These are:
- Newton’s First Law of Motion – The Law of Inertia
- Newton’s Second Law of Motion – The Law of Force and Acceleration
- Newton’s Third Law of Motion – The Law of Action and Reaction (not covered in detail here)
In this article, we focus on the first two.
Newton’s First Law of Motion: The Law of Inertia
Newton’s First Law of Motion states:
An object at rest will remain at rest, and an object in motion will continue in motion at a constant velocity unless acted upon by an external force.
This means objects don’t start moving, stop, or change direction unless something makes them do so. This resistance to changes in motion is called inertia.
Real-Life Application: Aircraft in Motion
According to Newton’s First Law of Motion, a plane flying steadily will keep flying at the same speed and direction unless another force acts on it. In aviation, four forces act on an aircraft:
- Lift
- Weight
- Thrust
- Drag
When thrust equals drag, the plane moves at a constant speed. But when thrust increases, the plane speeds up – demonstrating how external force affects motion.
Falling Objects and Newton’s First Law
Imagine dropping an object from a certain height. Before the drop, the object is still no motion, no air resistance. Once released, it accelerates due to gravity, increasing its speed. As air resistance builds, drag increases, balancing the weight eventually.
(Source: NASA Glenn Research Center, 2015)
Newton’s Second Law of Motion: Force Equals Mass Times Acceleration
Newton’s Second Law of Motion states:
The force acting on an object is equal to its mass multiplied by its acceleration (F = ma).
This means an object speeds up when a constant force acts upon it. Heavier objects require more force to move, and more force causes greater acceleration.
Real-Life Application: How Planes Accelerate
If a plane is cruising steadily (balanced lift and weight, balanced thrust and drag), it’s in equilibrium. But if the pilot increases thrust, the unbalanced force causes the aircraft to accelerate – changing its velocity.
Note: Airplane motion. Adapted from NASA (2021, May 13) NASA Glenn Research
As NASA illustrates, when net force increases, the aircraft’s motion changes accordingly.
Solve-It Section: Practice Newton’s Laws of Motion
Question 1: Newton’s First Law of Motion
Scenario: A person stands in an elevator moving upward at a constant speed. Their weight is 800 N. Suddenly, the elevator’s rope breaks and it begins to fall.
What is the normal force on the person before and after the rope breaks?
Solution:
- Before: Constant speed → no acceleration → net force = 0.
→ Normal force = weight = 800 N - After: Free fall → acceleration due to gravity → the floor no longer supports the person.
→ Normal force = 0 N
Question 2: Newton’s Second Law of Motion
Scenario: An aircraft cruises from point 0 to point 1. The force can be calculated as:
Constant Mass:
F = m × [(V1 – V0) / (t1 – t0)]
Changing Mass:
F = [(m1 × v1) – (m0 × v0)] / (t1 – t0)
This shows how acceleration or mass variation affects force using Newton’s Second Law of Motion.
Final Thoughts: Why Newton’s Laws of Motion Matter
Understanding Newton’s Laws of Motion helps explain everyday phenomena, from riding a bike to flying a jet. With Newton’s First Law of Motion, we learn that motion doesn’t change without force. With Newton’s Second Law of Motion, we understand how force and mass work together to produce motion.
Whether you’re a student, teacher, or just curious, these laws form the bedrock of classical physics – and their applications are truly all around us.
References
- Newton’s Laws of Motion. (2022). https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/newtons-laws-of-motion/
- Newton’s Three Laws of Motion. https://ccrma.stanford.edu/~jos/pasp/Newton_s_Three_Laws_Motion.html
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