# Mass

Mass is a very important concept in chemistry. When we learn about particles like protons, neutrons, electrons, atoms, ions and molecules later in the course, their mass is one of the key things we will look at. First, though, we need to understand what mass is.

## Mass is a property

Mass is a property which every object has. Is it a numerical property and the amount of mass an object has affects how it interacts with other objects.

The units of mass include grams, kilograms, micrograms, tons and pounds. In chemistry we mainly use grams and kilograms.

## Mass is usually positive, sometimes zero, but never negative

Most particles and other substances have a positive amount of mass.

There are some subatomic particles that have zero mass, however the particles that we will learn about in this course (including protons, neutrons, electrons, atoms, ions and molecules) all have positive masses.

It is thought to be impossible for anything to have a negative amount of mass.

## Mass Has Two Effects

Mass is a property which has two effects.

The first effect of mass is that it causes objects to be affected by the force of gravity. On Earth, this means that any object with a positive mass experiences the force of gravity pulling it down towards the earth. The more mass an object has, the stronger the force of gravitational attraction.

The coconut in this diagram has a mass of 1kg. Because it has a positive amount of mass, it is attracted towards the earth by the force of gravity.

The coconut in this diagram has a mass of 1kg. Because it has a positive amount of mass, it is attracted towards the earth by the force of gravity.

The second effect of mass is that it causes objects to resist changes in their speed or direction of movement.

For example, if a heavy truck is travelling quickly along a road, a lot of energy is required to slow it down or change its direction. This is because the truck has a large amount of mass and is therefore very resistant to these changes.

## Flashcards

Flashcards help you memorise information quickly. Copy each question onto its own flashcard and then write the answer on the other side. Testing yourself on these regularly will enable you to learn much more quickly than just reading and making notes.

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What is mass?

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What are the main units of mass used in chemistry?

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What are the possible values that mass can have?