Newtons Laws - The Three Laws of Motion, are:

  • NEWTON 1 - Inertia:
    An object at rest will remain at rest, and an object in motion will continue in motion unless acted on by an external force.
  • NEWTON 2 - Acceleration F=ma:
    Force = mass x acceleration. Acceleration can be either positive (increase in speed), or negative (decrease in speed).
  • NEWTON 3 - Consequence:
    For every action there is an equal and opposite re-action.

    Newtons three laws are essentially based on THREE responses to ONE action.

    The picture below shows Newton's 1st Law of Motion.


    An object at rest will remain at rest,

    UNLESS acted on by an external FORCE.

    The picture that follows also shows Newton's 1st Law of Motion.


    An object in motion will remain in motion,

    UNLESS acted on by an external FORCE.

    An external force can be many things, very often it is friction. Sometimes it is a brick wall / tree / lamp post /ground, or a kick, a push a shove.

    The pictures above and below illustrate Newton's 2nd Law of Motion.

    Force = mass x acceleration.

    The cat will progress in the direction in which it was kicked. His acceleration through the air will be dependent on the amount of enthusiasm / force with which he was propelled skywards.

    The force applied to succeed in this particular trajectory, will be dependent of the mass of the cat, multiplied by its acceleration.

    A greater force means more acceleration to an object of particular mass than a smaller force.

    A bigger cat would need a bigger force to follow the same trajectory and acceleration. In other words, if the cat were a lion, we could expect a different result.

    The picture also shows Newton's 3rd Law of Motion.


    For every action there is an equal and opposite reaction.

    Explained differently, when you push on something, it pushes back.

    The cat began his unexpected flight at the point that Lana kicked him. As she kicked the cat, she felt a force on her foot equal to, and in the opposite direction, to the force the cat felt on its body.


    No animals were harmed during the creation of this article.

    Please DO NOT use live animals when testing Newtons Laws.

    We recommend inanimate objects instead.

    Try an aeroplane. Don't kick it. Fly it.

    It's a much more productive way to experience Newtons Laws for yourself.

    If you still don't quite "get" Newton's Laws, then read a little further, otherwise feel free to explore your next topic.

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    NEWTONs Laws - 1st Law of Motion

    An object at rest will remain at rest, and an object in motion will continue in motion unless acted on by an external force.

    Imagine yourself, standing on the roof of a car. Your knees are bent, and the only thing holding you to the roof of the car is the tread on your shoes. The car is driving at 80km/hour. Suddenly, without warning, the driver slams on brakes to avoid a dog running across the road. What happens to you? That's right, you experience a brief and glorious moment of unexpected flight.

    That's Inertia.

    The car and you were moving together. You had no restraints attaching you to the car, so when the car stopped suddenly, there was nothing
    holding you to the car. There was an external force stopping the car, but there was initially no external force stopping you, (until your non-aerodynamic form slowed down rapidly,(external force 1 = drag), and came to a sudden halt when stopped by some other stationary object,(external force 2), the road ahead / lamp pole / tree etc...).

    Please don't try this.

    NEWTONs Laws - 2nd Law of Motion

    Force = mass x acceleration

    To understand this law of motion fully, it is best to define the terms involved.

    force = the "mojo", or "power" that causes an object to undergo some form of change. It either changes the object's position; changes the object's direction; or changes the object's physical shape.

    mass = a quantitative measure of an object's resistance to acceleration. In other words, a number you can use to get an idea how difficult it is to actually get a specific object moving.

    Folks often confuse "weight" with "mass". "Weight" is dependent
    on the gravitational force applied to the object in question.

    "Mass", however, relates to an object's composition and size.

    Imagine the fattest person you have ever seen. On earth, they will weigh a heck of a lot. On the moon, they will weigh significantly less. This is because weight is related to gravitational force, which is a lot less on the moon than back home. Their mass, however, their physical composition, carbon, water and so on, and the size of their clothes, will remain the same at either location.

    Now imagine trying to move the largest person you have ever seen to going somewhere they are not interested in going, and then imagine trying the same with the smallest person you have ever seen. Who is easier to move?

    acceleration = a change in speed and / or direction. It is a vector quantity. Vectors have both speed and direction. This means if something is slowing down, it is accelerating (negatively). If something is changing direction, it is accelerating. Anything that is accelerating cannot reach equilibrium.

    So let's recap: Newtons 2nd Law of motion states that Force = Mass x Acceleration (F=ma)

    From this we can conclude that an object will accelerate in the same direction as a force applied to it, and in proportion with that force.
    So shove a kid on roller-balls hard, and they will accelerate in the direction in which you shoved them rather quickly. Shove the same kid gently, and there won't be much acceleration. The acceleration is directly proportional to the whining of the kid, I mean the force of the shove.

    Take the fat person on roller-balls, shove them softly, and they are unlikely to go anywhere, because force is inversely proportional to mass... where the kid moved with little force, the larger person did not, the only difference being the mass to which the force was being applied.

    NEWTONs Laws - 3rd Law of Motion

    For every action there is an equal and opposite re-action.

    In other words, if you push on something, it pushes back.

    The best way I can think to explain this Law of Motion (ha ha) is to ask you to sit down in the closest available chair. Put your feet up on the closest available desk / coffee table / dog. Lean back, relax.

    I am assuming your chair has a backrest, if not, you would have fallen backwards, (and Newton's 2nd Law would then apply).

    Are you levitating? No? Okay, then the chair seat is pushing back on your rump, the chair back is pushing back on your back, and the desk / coffee table / dog is pushing back at your feet. There is an equal and opposite force to the one you are exerting on these three points keeping you in this comfortable position.

    Understand Newtons Laws now? I hope so!

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