Newton's Three Laws - Blog Posts

Newton's Three Laws of Motion

What are they?

Generally speaking, Newton's Three Laws of Motion are some of the most important laws in science. They are the fundamentals, and they are necessary for basic physics. They may seem complicated and jargon-y at first, but they are actually very understandable once broken down. So let's go over them!

Law of Inertia

Newton's Law of of Inertia states that "An object at rest remains at rest, and an object in motion remains in motion at constant speed and in a straight line unless acted on by an unbalanced force." 

First, let's go over inertia, which this law is about. Inertia is the tendency of objects to remain the same. So basically, what this law is saying is that an object that is not moving, will stay not moving, and an object that is moving will continue moving in the same direction and speed that it is going. The last phrase in this law, "unless acted on by an unbalanced force" is basically just saying that due to inertia, objects will remain the same unless another force (eg. gravity, friction, air resistance, etc.) changes/affects the object. 

For example: a marble rolling on the floor will continue rolling in the same direction and at the same speed. Common sense says this makes no sense because obviously, the marble would eventually stop rolling. This is because although it may not seem as obvious, there actually is a force acting on the marble--friction from the floor. The friction acting on the marble slows it down until it eventually comes to a stop. 

Law of Acceleration

Newton's Law of Acceleration states that "The acceleration of an object depends on the mass of the object and the amount of force applied."

Most times Newton's Second Law is summarized as the equation F = ma, where F = net force in a system, m = mass of object(s), and a = acceleration of object(s). This law is pretty simple, it mostly is just saying that the force applied to an object depends on the acceleration of the ojbect and the mass of the object, or any other variation of this statement. In practice, you just need to input the necessary information into this equation to solve for the unknown variable. One lovely thing about F = ma is its simplicity; it only requires basicaly algebra to solve and is easy to remember. It also merits a mention that of all the equations you need to memorize for school, this is one of the most important ones (especially for physics), it should be up there in your brain with c^2 = a^2+b^2 and the quadratic formula. 

Here's an example: If a 5 kg bowling ball is rolling down the bowling alley with an acceleration of 2 m/s^2, what is the force being applied to the bowling ball? To solve this simple problem, you can input the mass and acceleration of the bowling ball into F = ma, so F = 5 kg * 2 m/s^2, meaning the force applied to the bowling ball is 10 kg m/s^2, or 10 N.

(Note: Force is usually in N, or newtons, and kg m/s^2 = N)

Law of Action and Reaction

Newton's Law of Action and Reaction states that "Whenever one object exerts a force on another object, the second object exerts an equal and opposite on the first."

You've probably have heard the saying "What goes up must come down" before. Well, this law isn't too far off from that, and the concept is pretty similar. This law is actually pretty self-explanatory; it's basically saying that for every action force, there will be an opposing reaction force that is the same strength and in the opposite direction. The law also stipulates that the two objects in the action/reaction force pair are acting on two DIFFERENT objects (so an object won't exert a reaction force unto itself). It's pretty simple when put in words, but this law is best explained using examples. 

For instance: If you jump off a skateboard, you will go forward (the skateboard is pushing you), and the skateboard will go backwards (you are pushing the skateboard). 

Another example: When you jump on a trampoline, you go up and you will notice that the trampoline will (temporarily) go down. 

Summary

This graphic from Owlcation.com describes Newton's Laws quite well: