Matter amount {mass, physics}| is sum of elementary-particle amounts. Matter has spatial extension and divisibility. Mass has inertia. Mass is scalar quantity. Object interaction with universal field, such as Higgs field or technicolor field, causes mass.
Object mass has balance point {mass center} {center of mass} {center of gravity}. In calculations, total object mass can be at mass center.
balance
To find object mass center, hold object at a point off center, allow object to swing freely under gravity until it stops, draw vertical line through point, and repeat for two more points. The three lines intersect at mass center.
spin
Spinning objects spin around mass center.
example
People cannot pick up chairs while standing against walls, because chair-person combination has mass center beyond toes, and so they must tip over.
Objects tend to keep same direction and speed {inertia}| {matter, inertia}. Mass resists motion change. Inertia is resistance to acceleration.
cause
All universe masses exert gravity on object masses. All universe masses contribute to space-time curvature at space-time points. Objects take the geodesic shortest path between two space-time points. Geodesics are paths that keep same direction and speed. Inertia is following geodesics. Space-time curvature depends on mass, so inertia depends on mass. The dependence is the same. Mass and inertia are the same.
examples
It is harder to pull or push more massive object. If someone puts a big rock on your head and hits it with hammer, you do not feel the hit, because big mass changes motion slowly. People can rapidly pull smooth tablecloths out from under dishes on tables, without moving dishes.
Substances have mass per volume {density, physics}|: density = mass / volume. For example, boxes can have different masses inside, while volume stays the same, so densities can differ.
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Date Modified: 2022.0225