Sunday, February 3, 2013

What is Newton's First Law?

Science for Writers:  Newton's First Law
'Apple on books' from Science for Writers Logo and text created by me.

Welcome to the latest Science for Writers post. Last time we discussed storing data in DNA. In this, the first of a three part mini-series, I will explain Newton's First Law of motion.

I have put important words in bold. These words are important in physics and I will refer to them throughout the post. It isn't overly important for you to know the exact meaning, so long as you get the gist of what I'm talking about you will be fine following this post.

Writing Links are in italics and these discuss how the science could be used in writing.

What does it state?

Newton wrote in his book, Principa:
Law I:  Every body persists in its state of being at rest or of moving uniformly straight forward, except insofar as  it is compelled to change its state by force impressed.
Lets break it down before going further:

  • A body, is an object. An apple is a body. A car is a body. You are a body.
  • To persist means 'to continue'.
  • A state is the condition something is in.
  • Rest means not moving. Being in a state of rest means the body is not moving.
  • Uniform means constant. Being in the state of uniform motion means moving in a straight line at a constant velocity (for now just think of velocity as speed).
  • Change means to do something different to what it is currently doing.
  • A force makes a body do something.
  • Impressed is just a fancy way of saying that the force acts on the body.
Now we've split it up, it is easier to understand. In actuality it is just a wordy way of saying, 'Every object continues what it is doing until a force acts on it that makes it change.'

As with all good laws in physics there is an equation to go with it:

Newton's First Law
Image from
Now this may look scary, but that big E like symbol (the Greek letter sigma) just means 'the sum of'. The F stands for force. So, the left side of the equation simply tells you to add up all the forces acting on the body. The next bit is easy. That is, as I am sure you can all work out, the number 0.

So all the bit before the arrow is saying is that you can add up all the forces acting on an object and you will get 0. But not always. Remember the law states that a body will continue doing what its doing until a force makes it change? Well if, when you add up all the forces, you get 0 it means the body won't change what it's doing.

Writing Link:  Newton's first law is a good analogy to writing engaging plots/characters. Most stories start off with a character being normal. In my novel-in-progress it is Nathan driving out of a car park. If you don't add anything into the mix your character will keep being normal--stay at rest or in uniform motion. But, if you add something--a force, then they change.


Apple Falling
Image from
Creator: Dan Kosmayer
Imagine an apple on a pile of books. It isn't doing anything; when you add up all the forces acting on the apple you will get 0. Now push the apple. It moves. This is because you are exerting a force onto the apple and that force makes the apple moves.

If you add up all the forces now, you won't get 0. This is because the forces acting on the apple aren't balanced. Let's say you push it to the left. The force stopping it flying into the air (gravity) is equal to the force stopping it falling through the books and floor. However you have added a force to the side. As the apple isn't against a wall or something to push back, the apple will roll to the left.

You keep pushing the apple and now it falls off the stack of books. Why?

Well there is now an unbalanced force pulling the apple down. Gravity. There is no reaction force. That is nothing to push back.

Now imagine you are skateboarding. Or, if you're like me and don't skateboard, imagine someone else skateboarding. You're/She's going along pretty fast. In fact you/she are travelling at a constant speed in a straight line. Both the person and the skateboard are travelling at the same constant velocity (velocity is speed and direction).

Image from
Creator: Kozzi
The curb is suddenly in front of you/her. When you/she crash into the curb the skateboard stops moving. Why? Well, the change in state of motion is due to curb providing a reaction force that counters the movement of the skateboard.

But what about you/her? You/she fall off. Why? The curb isn't doing anything to you/her. You/she keep/s going at the velocity you/she were/was going at before. But why don't/doesn't you/she keep going? Well, there is now a different force stopping you/her. Gravity pulls you/her to the ground (as the skateboard is no longer there to counter it) and friction stops you/her from going any further.

Writing Link:  Carrying on from the previous Writing Link analogy we can think more about what happens when something changes out protagonist's path of uniform normality. What would happen if only part of the protagonist's life changes--as in the curb hits the skateboard? Does part of the protagonist's stop abruptly whilst the other part flounders around helplessly?

So, there you have it, Newton's First Law. That's it for this post. Please comment on this post below; I'd love to here from you. Share this post if you enjoyed it. There are social media buttons at the bottom of the post for your convenience.



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