Newton’s 3 Physical Laws of Motion

gray newton s cradle in close up photogaphy

The 3 laws of motion in Newton’s Words

The laws are: (1) Every object moves in a straight line unless acted upon by a force. (2) The acceleration of an object is directly proportional to the net force exerted and inversely proportional to the object’s mass. (3) For every action, there is an equal and opposite reaction.

A painted portrait of Isaac newton wearing a brown robe with curly hair looking off into the distance.
A Portrait of Isaac Newton

Law 1: A body in motion/rest stays in motion/rest unless acted on by an external force.

In the simplest terms, this law states that objects do not tend to change unless a force acts on them. In other words, if you get into your car and start the engine, it will remain at rest unless another outside force acts on it. If you hit the gas pedal then your car will move forward and continue moving until something stops it (like hitting something). You will notice your car will slow down without you adding more gas, that is due to friction and wind resistance. 

The same holds true in reverse: if an object is moving at 10 miles per hour and there is no outside influence then that object will continue moving at 10 miles per hour until some other outside influence stops it (like running out of gas).

Law 2: Force = Mass x Acceleration

This is the easiest of Newton’s three laws to understand. It can be simply stated as:

  • Force = Mass x Acceleration (F=ma)

In other words, force cannot exist without mass or acceleration. You can’t have a force without some object to apply it to, and you certainly can’t have an object accelerating if there isn’t any force acting on it.

Law 3: Action = Reaction

Action and reaction forces are equal in magnitude, opposite in direction, and always act on different objects.

Look at it this way, why don’t we fall through the floor when standing. We are indeed inflicting a force on the ground, but there is no acceleration. However, the floor is reacting with an equal force of our weight to make a net force of 0 Newtons. Cool, right! Another way to see it is why is it that we get pushed back in the opposite direction as the bullet when we shoot a gun? 

This law also explains why things tend not to fly off of shelves when they should: gravity pulls down on everything equally; if something falls off its shelf because it lacks support there will be nothing left holding it up; so its weight will fall straight down through empty air until it hits another surface like the floor or another shelf below where there’s still support for it (and hopefully no one was standing nearby).

Leave a Reply

%d bloggers like this: