Newton's Laws & Applications
Force diagrams, friction, connected bodies
Newton's Laws and Applications
First Law: objects remain at rest or in uniform motion unless acted on by a net force. Second Law: Fnet = ma. Third Law: every action has an equal and opposite reaction. These laws with force diagrams solve friction, tension, and connected-body problems.
Example
Worked Example
A 5 kg block is pushed with 30 N across a rough surface. Friction is 10 N. Fnet = 30 - 10 = 20 N. Acceleration: a = Fnet/m = 20/5 = 4 m/s squared. Always draw a free-body diagram showing all forces.
Note
Exam Tip
Include weight (mg), normal force, friction, applied force, and tension in free-body diagrams. Choose a positive direction and apply Newton's Second Law consistently.
Key Vocabulary
Net forceThe overall force acting on an object when all forces are combined
FrictionA force that opposes relative motion between surfaces in contact
Free-body diagramA diagram showing all forces acting on a single object
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