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Newton’s 3 Laws Of Motion Explained

Isaac Newton was one of the most important figures in the history of science. While we’ve written about him in the past, many of his laws of motion are still misunderstood. So we’ve put together this blog post to summarise each of his 3 laws of motion with the relevant equations and a real-life example:

First Law

Also known as the law of inertia; Newton’s first law of motion states that: “An object in motion will remain in motion and an object at rest will remain at rest unless acted upon by a force”. An example of this law is throwing balls: A light beachball will require a lot less force to move than a heavy bowling ball.

The second and third laws follow-on from this and use this first law to establish a frame of reference.

Second Law

The second law of motion states that: “Net force is equal to mass times acceleration”. This can be explained mathematically using the equation:


Where is the net force placed on the object, is the object’s mass and a, the acceleration.

An example of this force would be a hockey puck: When force is exerted on it whilst on a frictionless ice rink (or as close to frictionless as possible), nothing is cancelling out this force, so the puck accelerates forward until it comes into contact with a solid object, such as a goal, where the kinetic energy is transferred into the object, stopping the puck in it’s path. When the puck has stopped moving, this is known as equilibrium. Whilst in equilibrium, the puck could still be moving but its velocity won’t be changing.

Third Law

Newton’s third and probably most well-known law of motion states that: “For every action, there is an equal and opposite reaction”. Also known as the normal force, this law of motion is one of the easiest to observe but one of the hardest to understand intuitively.

As an example of this force in motion: Imagine a bowl with a sheet of aluminium foil sitting on top of it. If you were to place a grape on this foil it would exert force down onto the foil because gravity is pulling it downwards while the normal force exerts upwards by the same amount, stopping the foil from collapsing in on itself whilst keeping the grape in equilibrium. If you were to place a second grape on the foil, this would double the amount of force pushing downwards and also double the amount of normal force pushing upwards. Eventually, with enough grapes and, subsequently, downwards force added to the foil, it would collapse due to not being able to match the force from the weight placed on it.