Newton's Laws of Motion to Know for AP Physics 1

Newton's Laws of Motion explain how forces affect the movement of objects. These laws are foundational in physics, connecting concepts like inertia, acceleration, and action-reaction pairs, which are essential for understanding dynamics in various physical systems.

1. Newton's First Law of Motion (Law of Inertia)

   • An object at rest stays at rest, and an object in motion stays in motion unless acted upon by a net external force.
   • Inertia is the tendency of an object to resist changes in its state of motion.
   • This law implies that forces are necessary to change the velocity of an object.

2. Newton's Second Law of Motion (F = ma)

   • The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.
   • The formula F = ma quantifies the relationship between force (F), mass (m), and acceleration (a).
   • This law explains how the motion of an object changes when a force is applied.

3. Newton's Third Law of Motion (Action-Reaction)

   • For every action, there is an equal and opposite reaction.
   • Forces always occur in pairs; if object A exerts a force on object B, then object B exerts a force of equal magnitude and opposite direction on object A.
   • This principle is crucial for understanding interactions between objects.

4. Free-body diagrams

   • A free-body diagram is a visual representation of all the forces acting on an object.
   • It helps in analyzing the forces to determine the net force and resulting motion.
   • Each force is represented as an arrow pointing in the direction of the force, with its length proportional to the force's magnitude.

5. Forces: gravity, normal force, friction, tension

   • Gravity: The force that attracts two bodies toward each other, proportional to their masses and inversely proportional to the square of the distance between them.
   • Normal force: The support force exerted by a surface perpendicular to the object resting on it.
   • Friction: The force that opposes the relative motion of two surfaces in contact, dependent on the nature of the surfaces and the normal force.
   • Tension: The force transmitted through a string, rope, or cable when it is pulled tight by forces acting from opposite ends.

6. Mass vs. weight

   • Mass is a measure of the amount of matter in an object, typically measured in kilograms (kg).
   • Weight is the force exerted by gravity on an object, calculated as weight = mass × gravitational acceleration (W = mg).
   • Weight varies with the strength of the gravitational field, while mass remains constant regardless of location.

7. Equilibrium and net force

   • An object is in equilibrium when the net force acting on it is zero, resulting in no acceleration.
   • This can occur when all forces acting on an object balance each other out.
   • Understanding equilibrium is essential for analyzing static and dynamic systems.

8. Applying Newton's Laws to objects on inclined planes

   • The forces acting on an object on an incline include gravitational force, normal force, and friction.
   • The component of gravitational force acting parallel to the incline causes acceleration down the slope.
   • Free-body diagrams are particularly useful for resolving forces into components along the incline and perpendicular to it.

9. Centripetal force and circular motion

   • Centripetal force is the net force directed toward the center of a circular path, necessary for an object to maintain circular motion.
   • It is calculated using the formula F_c = (mv^2)/r, where m is mass, v is velocity, and r is the radius of the circular path.
   • Understanding centripetal force is crucial for analyzing motion in circular paths, such as satellites or cars on a curved road.

10. Momentum and impulse

    • Momentum (p) is the product of an object's mass and its velocity (p = mv) and is a vector quantity.
    • Impulse is the change in momentum resulting from a force applied over time, calculated as impulse = force × time (J = FΔt).
    • The principle of conservation of momentum states that in a closed system, the total momentum before an event equals the total momentum after the event.