Is “gravity,” a force or a concept?
I have been told it is both by different teachers.
Gravity is a force. it’s a vector having a magnitude and direction (this is additional information). That magnitude (9.8ms^-2) has a downwards direction pulling to the centre of the earth.
The teacher who told you it was a concept is right but so is everything else in classical mechanics.
Hi Harryperry, you’ve asked an awesome question. The word gravity can be a bit ambiguous, and the answer may change depending on what you mean, so I’m going to suggest a few terms:
Gravitational force - this is the force experienced by a mass inside a gravitational field. This is often called ‘weight’, or ‘force due to gravity’.
Gravtitational field - this field extends around any object with mass. Objects of mass inside that field experience a pulling force. The name of this pull is weight/gravitational force/force due to gravity. A stronger gravitational field would lead to a larger weight force.
So the term gravity on its own, could refer to either the field, or the force. This is why it can be useful to be more specific.
To consider the problem from another angle, we can look back at a hopefully familiar equation: F=mg, we have a force (F), mass (m), and what is often referred to as gravity (g). If we say the force is gravity as well as ‘g’, then we have a quantity defined as ‘gravity’ on both sides of the equation. In most cases F and g cannot be equal to each other, so we can’t identify both as gravity.
The units of F are Newtons, and ‘g’ is metres per second squared (acceleration due to a gravitational field) or Newtons per kilogram (gravitational field strength), so ‘g’ represents the gravitational field, whereas F represents the force due to gravity, also known as Weight.
Thinking about forces and fields in these terms may help if/when you come to explore more field related concepts in Level 3 Physics. For NCEA Level 1 and 2 (and mostly 3) you can get away with using the word gravity to mean weight, but I think it will help your understanding to be more specific.
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