This article discusses Newton’s second law of motion from a simple, layman’s approach. Plenty of examples are used in this article to improve clarity and familiarity. I advise you to take them with a healthy touch of skepticism.
Introduction to Newton’s second law
Russian scientist, Ivan Pavlov was investigating the digestion of dogs in 1897 when he made an exciting discovery. He noticed that the dogs started salivating even before the food was presented to them. The sound of an assistant pushing a cart down the hall, or the mere presentation of eating pots was enough motivation to get the dogs’ mouths watery.
This inspired him to digress and study the salivating response of dogs instead. Eventually, this line of study led him to develop the concept of classical conditioning and netting home the 1904 Nobel Prize for his work.
Perhaps inspired by Pavlov’s work, and undoubtedly motivated by his love for hotdogs, McDonald’s employee Mark Stonewall, conducted similar experiments on humans. Stonewall was interested in studying human behavior when presented with hyper-palatable food, such as a cold coke and a hotdog on a hot summer afternoon.
Stonewall discovered that young people were incredibly receptive. In fact, he reported that some of the younger folks salivated at the thought of a hotdog and coke alone. However, this enthusiasm seemed to drop with increasing age, with the older folks giving it so much as a passing thought.
Stonewall concluded that human behavior toward hyper-palatable foods was generally in the opposite direction with increasing age. Although he never won a Nobel Prize or any formal recognition for his work, Stonewall’s story serves as a smooth and familiar introduction to Newton’s second law of motion.
Quantitative statement of Newton’s law
Isaac Newton was a British physicist in the 1600s who conducted similar experiments to Pavlov’s and Stonewall’s, except not on dogs or human beings but on blocks of dry wood. Now, of course, blocks of wood don’t respond to food or other forms of stimuli common to dogs and human beings, but they respond to a force. In literal terms, they respond to a push or a pull caused by an agent in their environment.
Like Pavlov and Stonewall, he studied how his subjects (blocks of wood in this case), respond to a push or a pull. Newton analyzed his results and arrived at his conclusion: for the same force, lighter objects respond stronger than heavier objects.
In simple terms, kicking an empty bottle of water would send it flying off faster than a bottle full of water.
Defining Force
Isaac Newton measured the response of an object to a force with a quantity called “acceleration”. You can think of acceleration as “salivation” in Pavlov’s and Stonewall’s experiments. The stronger the force, the stronger the acceleration in the same way as the stronger the urge for food, the stronger the salivation.
The experiment he did, went something like this:
- He took a sample block and noted its weight. Then he hooked up the block to an extended string and measured its acceleration “response” to the force.
- He repeated the experiment for another set of blocks, twice the weight of the first block, and noted the acceleration.
- He repeated the experiment for another set of blocks, increasing the weight of the previous blocks on every turn.
In his experiments, Newton developed the following expression for Force, Mass, and Acceleration.
F=ma
By the way, have you ever wondered what happens when an unstoppable force meets an immovable object?
Statement of Newton’s second law of motion
Newton’s second law of motion states, “for an unchanging mass, force equals mass times acceleration.”
The most important part of Newton’s investigations was that he was able to quantify force. That is, instead of saying, “I pulled my car very strongly”, you can now say, “I towed my car with a force of 1100N.” As it turns out, this is very important in plenty of theoretical and practical developments of physics.
