Momentum — The key idea

The key idea

Linear momentum is the vector quantity p = mv. For an isolated system, total momentum remains constant.

Why it matters

Linear momentum is the vector quantity p = mv. For an isolated system, total momentum remains constant.

A picture to remember

Before calculating, identify what the quantities represent, their units and the direction in which you expect the result to change. For Momentum, this simple prediction is a useful check: it forces you to connect the symbols or vocabulary to a physical or chemical meaning.

Momentum

Choose a concrete case linked to Momentum. Write down the known information, what you are trying to find, and the units. Then state the rule, model or trend you will use. If a calculation is involved, keep the units visible at every line; if it is conceptual, state what changes and what remains fixed.

The key idea

A strong answer contains four things: the starting situation, the variable that changes, the direction or numerical result, and one check. The check can be a unit, an order of magnitude, a limiting case or a comparison with a familiar example.