Overview
This lecture introduces Newton's three laws of motion, explaining how forces affect movement and acceleration of objects using real-world examples.
Newton’s Laws of Motion
- Newton’s first law states that an object remains at rest or in motion unless acted upon by a net force (law of inertia).
- Inertia is an object’s resistance to changing its motion; it depends on mass.
- Newton’s second law: Net force equals mass times acceleration (F(net) = ma).
- Net force is the total force after all opposing forces are accounted for.
- An object is in equilibrium when the net force on it is zero, so its velocity does not change.
- Newton’s third law: For every action, there is an equal and opposite reaction.
Types of Forces
- The force of gravity on an object is its weight, calculated as F(g) = mg, where g = 9.81 m/s².
- Weight is measured in Newtons (N), while mass is in kilograms (kg).
- The normal force is a perpendicular force from a surface that balances other forces (like gravity), changing magnitude as needed.
- Tension force is the pulling force transmitted by a string, rope, or cable when it is taut.
Free Body Diagrams & Problem Solving
- Free body diagrams represent objects and all forces acting on them with labeled arrows.
- When solving force problems, always draw a free body diagram and define force directions.
- In systems with ropes or pulleys (like elevators), set up equations for each object to solve for unknowns like acceleration.
- For multiple objects connected (e.g., elevator and counterweight), use algebra to eliminate unknowns and solve for net acceleration.
Example Calculations
- Example: For a 5 kg ball, the force of gravity is F = mg = 49.05 N (using g = 9.81 m/s²).
- For an elevator and counterweight, net acceleration is found by dividing the net force by the total mass of the system.
Key Terms & Definitions
- Inertia — the tendency of an object to resist changes in its motion.
- Net Force — the sum of all forces acting on an object.
- Equilibrium — a state where net force is zero and velocity is constant.
- Normal Force — the perpendicular force exerted by a surface on an object.
- Tension Force — the force transmitted through a string, rope, or cable.
- Weight — the force of gravity on an object (F = mg).
Action Items / Next Steps
- Practice drawing free body diagrams for various scenarios.
- Solve example problems using Newton’s laws and force equations.