Last updated: August 4, 2019
Topic: SciencePhysics
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Newton’s Understanding of the Universe

    Isaac Newton is widely known for discovering the concept of gravity when an apple fell of a tree and hit his head. Despite if this actually happened or not, Isaac Newton is responsible for many discoveries that have helped fellow physicists and physics students everywhere to this day with their understanding of the complex subject that is physics. Some of his most important discoveries include his work on lights and prisms, calculus, the telescope, and gravity. In this section we are going to be focusing on his discovery of the three laws of motion and the universal law of gravitation which have greatly impacted our understanding of physics and everyday interactions.

Newton’s Three Laws of Motion:

Newton’s three laws of motion are able to describe the impact forces have on an object and its motion as a result of these forces. These laws can be applied in various situations in everyday life, making it simpler to understand compared to other theories such as Einstein’s theory of relativity (don’t worry, we won’t hurt your brain with that one just yet!)

Newton’s First Law of Motion

This law states that an object will stay at rest or travel in the same direction unless an external force acts on the object. It relates to the concept of inertia which is where an object will remain in the same state unless a force acts upon it. Objects in motion tend to stay in that motion whereas objects at rest tend to stay at rest. It is important to consider net force when discussing Newton’s laws. Objects have a net force of zero which allows them to continue to move in the motion that they are. When you apply a force to the object, the net force is no longer zero and the object faces a change in motion.  This can be seen in everyday life situations. When you get into a car crash, your body would keep moving in the direction you were travelling, if it wasn’t for your seatbelt. Your seatbelt is the force that causes you to come to a rest. If not, then you would go flying out the window as your body will remain in motion even though the car comes to a stop.


Newton’s Second Law of Motion

Newton’s second law displays the relationship between the net force, mass, and acceleration of an object. This law states that force is equal to mass multiplied by the acceleration of an object. The amount of force you apply to an object will have a different impact on a lighter object’s acceleration compared to a heavier object’s acceleration. For example, the amount of force you use to push a box will cause the box to accelerate. However, if you use that same force to push a car, it is likely you won’t cause it to accelerate as much as the box (unless you are superman).

Newton’s Third Law of Motion

Newton’s third law of motion states that every action, always has an opposite and equal reaction. This law explains that in every interaction there is a pair of forces acting on two different objects. This can be seen for an example as simple as the act of you sitting on a chair. While you are sitting, you are applying a normal force to the chair and the chair is applying a normal force back at you. This can be demonstrated through your FBD diagrams where you must label the force pairs in third law notation.



Newton’s Universal Law of Gravitation

Newton proposed that gravity is a universal force as he was not satisfied with Kepler’s discoveries.  He used this concept to explain Kepler’s laws who previously believed that planets were somehow magnetically driven by the sun to their orbits. Newton came upon the discovery through his observations as he wondered what kept the stars and planets from falling. The universal law of gravitation states that any two objects are attracted to each other through the force of gravity each object exerts. The force is directly proportional to mass and inversely proportional to the square of the distance between them. This law helps support the idea that gravity is a universal concept. In this equation, Newton knew there was a constant at work, but it was Henry Cavendish who discovered the constant and contributed his value of “G” to the equation. This concept helped prove that the sun was indeed the center of the solar system as many people had trouble believing this.


Newton played an important role in the scientific revolution with his discoveries helping in various fields. He influenced other scientists, helping in their own discoveries. His discovery of the three laws of motion and the universal law of gravitation allow us to analyze everyday situations and allow us to gain a better understanding of how objects behave the way they do. His laws can be applied to both complex and simple situations allowing them to be used by various people in different fields.