Key idea
Newton's laws
Deuxième loi : ΣF = ma
Newton’s laws connect forces to changes in motion. In an inertial frame, the net force determines acceleration through the relation F = ma.
Newton's laws
The key idea
Newton’s laws connect forces to changes in motion. In an inertial frame, the net force determines acceleration through the relation F = ma.
Why it matters
The laws are powerful because they turn a force diagram into predictions about motion; the difficult part is often identifying the system and forces correctly.
A picture to remember
Key idea
Newton's laws
Guided example
Newton's laws
Newton’s laws connect forces to changes in motion. In an inertial frame, the net force determines acceleration through the relation F = ma.
Put it into practice
Newton's laws
Choose a concrete case linked to Newton's laws. 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.
Check your answer
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.