 # Let’s Get Physics-l: Force and the Newton

Force is something we have discussed an awful lot as of late but, at the end of day, what is it? The definition often associated to it is that it’s an influence that causes a change in motion of a body or stress in an object. Force is measured in Newtons, a newton being defined as the force needed to move a 1kg mass at an acceleration of 1 ms^-2. At it’s root this is true but force isn’t that simple.

Mass and Acceleration

Remember Newton’s Second Law of Motion? The one which says that resultant force equates to the rate of change of momentum of an object (If I’m honest, it’s the one I always forget)? Well Mass and Acceleration are a big part of this.

The equation F=ma is arguably one of the most famous equations in Physics, second only to E=mc^2. Newton observed that if no resultant force (A single force that has the same effect as the sum of all the forces acting on an object)  was acting on an object it didn’t accelerate which the equation above proved. Note, Force causes acceleration, not the other way round.

Weight

Weight is a force. In fact, the equation of weight is almost exactly the same as the equation F=ma, we simply know something before we even begin (Assuming, that is, we are on Earth as we launch projectiles up in the air). The Equation for weight is:

## W = mg

Where:

• W is Weight, measured in N
• m is Mass, measured in kg
• g is acceleration due to gravity (Sound familiar?) which is 9.81 ms^-2 on Earth

The Four Fundamental Forces of Nature

Though the number may be small, the forces of nature are really important as they are literally responsible for all the interactions between bodies and waves in our Universe (Side note: A superhero team based on them would be awesome… Hmmm…). Some are more observable than others but all are equally important.

Gravitational force

Perhaps the one people are most familiar with and one that keeps the Universe in order. Everything in our Universe experiences the influence of gravitation. It occurs between two bodies but that’s not to say it exclusively between those two. We wouldn’t have a solar system if the Sun just shared a gravitational force with Mercury. This force is directly proportional to the masses of the two but inversely proportional to the square of their separation.

Think of gravitational force as a sort of bond between you and a significant other be it your best friend, partner or your local postman (It’s not weird to be fond of your post man!). Mass, in this instance, is stuff you share an interest in be it comic books, sports or collecting novelty tooth brushes, whatever. The more shared interests you have, the stronger your relationship. Distance in this instance remains the same. The further away your friend is the weaker your bond. (Note: I’m stereotyping a lot here. Relationships are more complex than this, or so I’m lead to believe).

Gravitational force is the force that keeps the universe as it is, is always attractive and has an infinite range.

Electromagnetic Force

Electromagnetic forces are what the stuff around us together. It’s the force that holds atoms and molecules together. On a molecular/ atomic level it’s the exchange of photons between charged particles or magnetic materials which keeps everything working, sort of like a society where everyone shares with their neighbours to keep things running smoothly. Unlike gravitational force, it can be both repulsive and attractive but it does share it’s infinite range.

Weak Interaction

This is the force that is responsible for radioactive decay. It is weak in nature and it’s range is really, really short, a mere 10^-18 metres. This is the one force that we don’t really experience it on a day to day basis but it is one that is still important.

Strong Interaction

This force holds subatomic particles in the nucleus together. Because every atom has a nucleus and atoms make up so much of the world around us, the force is super strong. That being said, it acts over a really short range, about 10^-15 metres.

Summary

• Force – an influence that causes change in motion/speed or causes and object to feel stress/ pressure
• Resultant Force – A single force that has the same effect as the sum of all the forces acting on a object
• The Newton – The force that causes a 1kg mass to accelerate at 1 ms^-2
• F = ma – Supports Newton’s Second Law of Motion
• No resultant force – No acceleration
• W = mg
• W – Weight
• m – Mass
• g – Acceleration due to gravity
• Four fundamental forces of nature
• Gravitational force – Weakest – Causes planets to orbit stars, for example
• Electromagnetic force – Holds atoms and molecules together
• Weak Interaction – Radioactive Decay – Really short range
• Strong Interaction – Subatomic Particles in the nucleus

An insight into a really important part of physics. If you have any thoughts or questions please feel free to leave them in the comments.