# a particular mass

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#### forgoodorill

##### Senior Member
Hi, everyone!

Consider a game of snooker. The cue ball has a particular mass, and is at rest. You hit the cue ball with the cue, with a particular force and in a particular direction(towards the black, say).

So what's the meaning of 'mass' here? I couldn't find a proper one in the dictionary. I guess it means 'condition' here. But the dictionary doesn't exist this one. Only similar one to this is: a large amount of something that has no particular shape or arrangement:

• #### entangledbank

##### Senior Member
Mass is the scientific term for what, outside of science, we call weight: a snooker ball has a mass of 100 grams, or whatever. In your sentence 'mass' is used because force and velocity and position are probably going to be discussed.

#### Rover_KE

##### Senior Member
Hi, everyone!
Please tell us the title and author of said book.

#### heypresto

##### Senior Member
It's the scientific meaning of mass.

From the WR Dictionary: Physics [uncountable] the quantity or amount of physical matter of a thing as figured from its weight or from Newton's second law of motion. Abbr.: m

Or the 'm' in E = mc2

#### forgoodorill

##### Senior Member
Sorry, I forget to write its name: reading metaphysics.

#### Rover_KE

##### Senior Member
Thank you ... and the author?

##### Senior Member
There is no standard mass for snooker balls, but they all tend to be about 167 grammes. That is their mass everywhere in the universe.

On earth, under earth gravity, they also weigh 167 grammes because this is where snooker (and the gramme) were invented. On the moon they weigh 28 grammes. In outer space they weigh nothing.

#### kentix

##### Senior Member
To be very precise, grams are a measure of mass, not weight. If a snooker ball has a mass of 167 grams on Earth then it has the same mass on the moon and in space. Mass is an inherent property of an object.

Weight comes from gravity acting on a mass. The standard metric unit of weight is the newton. A snooker ball on the moon has the same mass but weighs less because the gravity acting on it is less.

Because in the past all weights were essentially measured at the earth's surface the concept of weight and mass was intermingled. So when people say something weighs 100 kilos they really mean it has a mass of 100 kilos, and therefore a weight of 980 newtons at the Earth's surface. As long as you don't leave the Earth's surface there's no difference and one can be used in place of the other. When you go somewhere else in the universe that changes.

On the moon that same object would still have a mass of 100 kg but it's weight would only be 163 newtons (instead of 980).

It's very important to distinguish between the two in physics problems.

#### Rover_KE

##### Senior Member
Then I don't know how you're going to understand the rest of the book.

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