Newton’s Laws of Motion
First Law Principle: If net force on a body is zero, the body maintains constant velocity (at rest or in motion). Implication: If net force is not zero, velocity changes (acceleration occurs). Formula: ( a = \frac{\Sigma F}{m} ) Example Question: "A hockey puck slides on ice at a constant velocity. What can we conclude about the net force acting on it?" Explanation: Since the puck maintains constant velocity, the net force acting on it is zero according to Newton's First Law.
Second Law Defined by the relationship between force, mass, and acceleration. Formula: ( F = ma ) Example Question: "If a 5-kg object is acted upon by a force of 20 N, what is its acceleration?" Explanation: Using the formula F = ma, we rearrange to find acceleration: a = F/m = 20 N / 5 kg = 4 m/s².
Third Law Principle: For every action, there is an equal and opposite reaction. Example: If object A exerts a force on object B, B exerts an equal and opposite force on A.
Collision Question (4.40) Scenario: Collision between a 1000-kg car and a 2500-kg car. Force Experience: Both cars experience the same force (Newton's Third Law). Acceleration: The lighter car (1000-kg) experiences greater acceleration due to lower mass (derived from ( a = \frac{F}{m} )). Injury Likelihood: Passengers in the smaller car are more likely to be injured due to differences in momentum and crumple zone effectiveness, despite equal body strength.
Free-Body Diagrams (Problem 4.29) Scenario: A ball hanging from a string in a moving train. Cases: Uniform Velocity: Diagram shows tension and weight acting on the ball. Net force: Zero (ball remains motionless relative to the train). Speeding Up Uniformly: Diagram includes tension and effects of acceleration. Net force: Not zero as acceleration acts downward relative to the train's frame.
Fundamental Concepts in Physics Matter and Interactions Composition: Matter consists of atoms, each composed of a nucleus (containing protons and neutrons) and electrons. Elementary Particles: Protons and neutrons consist of quarks; quarks and electrons are considered fundamental particles. Fundamental Interactions Types: Gravitational Electromagnetic Strong Weak Gravitation and electromagnetism account for most everyday interactions.
Examples of Forces Common forces include: Pulls, pushes, normal force, friction, resistance, elastic force, gravity, electric force, and magnetic force. Weight: Described by ( W = mg ) (where g is acceleration due to gravity). Force directed towards Earth's center (downward). Tension Definition: Arises from electromagnetic interactions; acts along strings/ropes. Characteristics: Tension is a contact force. Passive force; magnitude adjusts to balance other acting forces.
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