Let’s Get Physics-l: Newton’s First Law of Motion

(Please note: The characters used in my examples were created by Marvel and in no way belong to me. They are being used here to help demonstrate the topic in action. Thank you)

Isaac Newton is attributed with many scientific discoveries including the discovery of the force gravity and his 3 laws of motion (Though Galileo did technically discover gravity before Newton. Fear not, he does credit Galileo in the quote “If I have seen further than other men, it is because I have stood on the shoulders of giants.” The giant here being Galileo. I digress, though it is more relevant than previous digressions). We will focus on the first of these 3 laws.

Newton’s First Law of Motion states:

An object will remain stationary or at a constant velocity moving in a straight line so long as no external forces act upon it.

Basically, something will remain at rest or at a constant speed in one direction unless a force acts upon it to change this. We can break this up into 4 principles which are as follows:

1) An object will remain stationary if no (net) resultant force acts upon it

 

Image result for Avenjet
Avenjet, for those who aren’t aware of what it looks like

Time for some superhero examples (A little overdue (Well, I think so))! Imagine the Avengers’ jet, the Avenjet (See above), parked at Avengers tower. Whilst parked, the Avenjet is said to be stationary or at rest. It will remain parked (at rest) if no external forces, like thrust from the engine, act upon it. This, in effect, is the first principle of Newton’s First Law.

2) An object can change direction if a resultant force acts upon it

Oh no! Ultron is causing havoc on the streets of Manhattan! The Avengers are in a hurry to get the scene so take the Avenjet. At present, the Avenjet is flying in a straight line towards Time Square. Suddenly, Ultron fires an energy blast directly at the Avenjet. Thankfully, Black Widow (The pilot at the time) swerves and avoids the shot. This change in direction is caused by an increased up thrust in the left (or right, it’s up to you) wing which is greater than the effect of gravity, allowing the Avenjet to continue its course undamaged. This is the second principle of Newton’s First Law.

3) An object can accelerate/decelerate if a net resultant force acts upon it

Landing the Avenjet proves too difficult with Ultron’s robot army covering the entire area, The Avengers are going to have to make a freefall down into the battle. To reduce the chance of injury (Though freefalling itself is a bit risky), Black Widow slows the Avenjet down to a reasonable speed from which the likes of Captain America, Hawkeye and herself can jump from. She reduces the thrust generated by the engines so that the resistive force of air resistance is greater than that of the thrust, causing the Avenjet to decelerate. Before launching herself into battle, she switches on autopilot. Once she jumps out, the Avenjet rushes back to Avengers Tower in 10 seconds flat. The thrust generated by the engines to make it back in this time is greater than the air resistance effecting the Avenjet, causing the Avenjet to accelerate.  This is the third principle of Newton’s First Law.

4) If an object is travelling at a constant velocity then no (net) resultant force is acting on it

Ultron is defeated! The Avengers are rather tired, as one would expect after fighting a crazy robot army, and they call the Avenjet back to take them to the Tower. On the return journey, the Avenjet flies straight at the same speed as the thrust generated by the engine is equal to the air resistance acting on the Avenjet. This is the fourth and final principle of Newton’s First Law.


Summary:

  • Newton 1st Law: An object will remain stationary or at a constant velocity moving in a straight line so long as no external forces act upon it. So:
    • An object will remain at rest if no external forces act on it
    • An object can change direction if it has a resultant force
    • An object can accelerate/decelerate if it has a resultant force
    • An object will remain at a constant velocity if it has no resultant force

So that’s Newton’s First Law. I hope my examples weren’t too confusing with the addition of some excellent storytelling (I think I’m hilarious but I’m probably just confused). As ever, if you have any thoughts, feedback or questions please feel free to leave them in the comments.

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