Gravity - Force or Field

[SionR25]

Hi everyone,

Recently I was asked in an a level physics paper the force acting down on a dropped object. I wrote gravity but the actual answer was weight as on the specification gravity is a field. Also in the course we are taught the four fundamental forces; weak nuclear, strong nuclear, electromagnetic and gravity. I understand that for my exam I need to stick to the specification , but could anyone here clear up which gravity is, or is it both in terms of the context?

Many thanks

Sion

[JamesF]

I think the problem here is that we tend, both in common use and in physics, to use the term "gravity" as shorthand. I might be tempted to suggest that terminology is clearer if we said the four fundamental interactions are the weak nuclear force, strong nuclear force, electromagnetic force and gravitational force, the latter being the "force due to gravity". In everyday use we call the latter "weight".

James

[SionR25]

Ahh, thanks for clearing that up

[RichardL]

The answer "gravity" will rarely get you a mark, Sion. Gravity is the name of a phenomenon, and just naming it would not be considered as an A level answer. Are you doing a year 1 unit, or is it year 2? Your question suggests year 1, in which case you are probably likely to be dealing with objects in free fall, or on surfaces, or hanging from ropes, etc. The full description of the "gravity" force would then be "gravitational force on the object due to the pull of the Earth". Depending on the context you might get credit for "weight", or even "mg", but check the mark scheme (if you can) to see what the exam board will accept.

[acey]

Interesting one, this. "Force" is a term of Newtonian physics, but not of relativistic physics. So the four fundamental "forces" are, strictly speaking, fundamental interactions, mediated by fields. But obviously the word "force" continues to be used in all sorts of ways(we still speak of "police forces"!) so "fundamental forces" can be taken loosely, rather than being seen as a statement that elementary particles are governed by Newtonian physics.

In a test paper, if there are various arrows asking you to name the forces, then you'll most likely be looking for things like "weight", "reaction", "air resistance" etc.

Main thing, as RichardL says, is to check the mark scheme and aim to give the sort of answers the examiners are looking for. In actual physics there may be lots of possible answers, but in an exam paper that isn't always the case.

Good luck with your studies!

[JulianO]

I always think the weak force is badly named - its not really a force at all.

[Tiki]

Just this.

...Gravity is the name of a phenomenon, ...

[Ganymede12]

Isn't gravity a dent in spacetime? Like a heavy ball on a stretched out sheet. The ball makes a dip in the sheet and lighter balls near the sheet get drawn towards it.

[badgerchap]

I have seen with increasing frequency physicists referring to the 4 fundamental interactions rafter than forces. This helps to remind oneself of the definition