Lesson 02
Forces and Newtons laws
Once you know how motion behaves, forces tell you why it changes. The key skill is building a clean free-body diagram, combining the forces, and then using F = m a.
Newtons three laws
First law: zero net force means zero acceleration.
Second law: acceleration points in the direction of the net force and has size F / m.
Third law: interaction forces come in equal and opposite pairs on different objects.
Problem-solving checklist
- 1. Draw every force acting on the object.
- 2. Choose positive directions and write the net-force equation.
- 3. Add friction or normal-force relationships if the surface matters.
- 4. Solve for acceleration, force, or tension after combining terms.
Next step
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Mark this lesson complete when the main idea feels clear, then move straight into practice while it is fresh.
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Quick reference
- Second law
- F_net = m a
- Weight
- W = m g
- Friction
- f = mu N