Home > Courses > 1P21_Crandles > Dynamics Mechanics and Waves Introduction Kinematics: motion in one and two dimensions Dynamics Newton's First and Second Laws The "natural" state of an object: Aristotle vs. Galileo Frames of Reference Newton's First Law Definition: mass and inertia Net Force and Newton's Second Law MC: net force and acceleration Ex: two horizontal forces Ex: ranking net force and acceleration Ex: a skydiver Ex: compare the masses Ex: a ship Inertial reference frames Reference Frames Definition of inertial reference frame Inertial Reference Frames Non-Inertial Reference Frames and fictitious forces Fictitious Forces: e.g.Coriolus Force Ex: which are inertial frames of reference? the laws of physics are independent of reference frame Types of Forces Non-contact forces: gravitational force Universal law of gravitation Universal law and acceleration due to gravity acceleration due to gravity on different planets Constant acceleration near the surface mass (inertia - scalar ) is NOT weight (force of gravity - vector) Contact forces Normal Force: molecular "spring mattress" is the origin of normal force Frictional Force: molecular "cold welds" is the origin of friction Tension: massless rope is a perfect transmitter of force: straight or wrapped around an ideal pulley Free Body Diagrams free body diagram elevator accelerating upward free body diagram of a rocket propelled ice block free body diagram of a skier being towed up a hill MC: Which is the correct FBD ? MC: lowering a crate MC: motion in an elevator I MC: motion in an elevator II Ex: In which rope is tension larger? Ex: rappelling down a cliff Newton's Third Law MC: identify action-reaction pair I MC: identify action-reaction pair II MC: a collision MC: father and daughter on skates MC: tug of war MC: motion in an elevator III Coupled Objects Two blocks on frictionless surface MC: two coupled hanging objects Ex: motion with a pulley I MC: motion with a pulley II Frictional Force molecular "cold welds" is the origin of friction Static Friction implies no slipping; balances applied force Static Friction has variable magnitude Kinetic Friction occurs when an object is sliding; is opposite to motion Kinetic Friction has has approximately constant value MC: pushing a box on rough surface MC: pushing a heavy crate MC: box on the bed of a truck MC: static vs. kinetic friction Ex: accelerating on ice Ex: static vs. kinetic friction MC: pulling a block 1 MC: pulling a block 2 MC: pulling a block 3 MC: block against wall Ex: pushing two blocks Drag and terminal velocity Drag force depends on velocity: low speed Drag force depends on velocity:greater speed Drag force depends on velocity: terminal velocity MC: ball thrown down with speed 30 m/s, terminal velocity is 15 m/s MC: opening a parachute Linearly Constrained Motion Uniform Circular Motion Centripetal Acceleration uniform circular motion defined angular position, frequency period angular velocity and tangential velocity Every particle in rigid body shares same ω but tangential velocity depends on radius Direction of centripetal acceleration MC: centripetal acceleration I MC: centripetal acceleration II MC: centripetal acceleration III Ex: tight and gentle turns the kinematic equations do NOT apply to uniform circular motion non-uniform circular motion: a = at + ac (a model plane, a discus thrower) N2L: Net Force must provide centripetal acceleration a model airplane, Fc = T provided by tension in the wire a turning car, Fc = fs provided by friction a banked road, Fc provided by the normal force A carnival ride, Fc provided by the tension force MC: dip in the road MC: hill on the road MC: ferris wheel MC: ball moving on a string in a vertical circle Gravitational Force and Kepler's Laws MC: gravitational force I MC: gravitational force II MC: gravitational force III MC: gravitational force IV Ex: three objects in a line in outer space Big "G" vs. little "g" perspectives MC: Weight and gravitational force Terrestrial versus celestial dynamics An old distinction: Celestial Physics vs. terrestrial physics solar system planetary orbit eccentricity planetary data Kepler's laws Weightlessness in the international space station Terrestrial and Celestial Dynamics are the same In orbit, an object is continuously falling an orbiting satellite, Fc provided by gravity Rotational motion Work, energy, momentum Oscillations and waves