Newtons Laws of Motion

Isaac Newton, a famous physicist, developed three laws of motion in 1687. The universe and every one of us obey these laws every day with every single movement that we make. These laws and examples of each are detailed below.

Newton’s First Law of Motion

Newton’s first law of Motion, commonly known as the inertia law, states the following: “An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force”.

So to make sense of that mumbo jumbo, think of it this way: Newton’s First Law is the ‘Lazy Law’. An object will keep doing what it is doing unless it is acted upon by another force. (The object is lazy)

If you think about this it does make sense: a moving object will only slow down due to the friction force acting against, provided there are no obstacles in the way. For example when someone is ice skating there is little friction from the ice opposing their movement (although there is air resistance/friction) – so their speed only changes a little when they are gliding across the ice, it feels like they could glide for a very long time

Have you ever played corners in a car? This is another example of Newton’s First Law at work. When the car rounds the corner, the car changes direction, yet the passengers keep moving in the same direction. The car therefore ‘pushes’ against the passengers as the car and the passengers are moving in different directions. The passengers can feel this push and can ‘fall into the corners’. Momentum keeps the passengers going in the same direction, yet the car applies a force to them, which changes their direction, and this can be felt.

Newton’s Second Law of Motion

Newton’s second Law of motion states that: “The acceleration of an object is directly proportional to the unbalanced force acting on it and inversely proportional to its mass” This law can be neatly summarized as the equation F=ma. If you are clever enough at mathematics you should be able to remember this law by simply remembering the equation F=ma and ‘describing it in words’. However if you need a little help understanding what this means think of the law as: If the mass or acceleration of an object is greater its force is greater.

This law can be a little tricky to make sense of at first, but instinctively we all know it. Which hurts more: A shotput falling from the sky at the accelerating due to the force of gravity (9.8ms^-2), or a box of tissues accelerating due to gravity? Is a faster moving object of the same weight going to hurt more when it hits you then the slower moving object?

This Law is particularly useful as it entails an equation that can be used to solve unknowns in physics. If you can figure out two of values in the equation F=ma, you can figure out the third. Some ways to rearrange this equation are as follows:

F=ma, a=F/m, m=F/a

Newton’s Third Law of Motion

Newton’s Third Law of motion can easily be summarized as meaning: “For every action there is an equal and opposite reaction”. So basically if I push a wall with a force of 60N it will push back at me also with a force of 60N

At first this idea can seem a little confusing, but if you think about it you can see how everyone utilizes this law in their everyday lives. For example when someone jumps what they are really doing is pushing against the ground. The force that they are pushing against the ground creates an equal and opposite reaction force from the ground, which pushes them into the sky causing them to ‘jump’.

Another example of Newton’s Third Law is that of a rocket ship taking off. It pushes on the ground/air with all the fire and power of its engine. This causes a reaction force from the ground and pushes the rocket up into the air.

So there you go; an explanation of Newton’s three laws of motion, complete with examples. An easy way to remember the laws is to remember Newton’s first law as the ‘lazy’ inertia law. To remember the second law think of the equation F=ma. Finally for the third law it is simply easy to remember that for every action there is an equal and opposite reaction.