Home > Courses > 1P21_Crandles > WorkEnergyMomentum Mechanics and Waves Introduction Kinematics: motion in one and two dimensions Dynamics Rotational motion Work, energy, momentum Work and Kinetic Energy work done by constant force along a straight path MC: Rank the work done MC: How does the work change? MC: How many forces are doing work? Work- Kinetic Energy Theorem K.E.= ability to do work MC: work-energy theorem I MC: work-energy theorem II MC: a sailboat work done along a curved path work done by a variable force Conservative vs. Non-Conservative Forces: Potential Energy definition: conservative forces MC: work done by conservative and non-conservative forces I MC: work done by conservative and non-conservative forces II definition of potential energy: ΔU=-Wc gravitational potential energy, U=mgh with respect to a reference height spring potential energy, U=(1/2)kx2 Ex: change in U does not depend on path: a skier Conservation of Mechanical Energy If Wnc=0 then Δ (U+K)=0 conversion of U to K: a bobsled Discuss: When is total mechanical energy conserved? MC: throwing balls from the roof MC: ski jump Ex: role of tension: a swimming hole Do you truly believe in the conservation of mechanical energy? Ex: A problem with friction Ex: A problem with a spring I Ex: A problem with a spring II Power = rate of doing work Linear momentum momentum of a particle and a system of particles impulse-momentum theorem Newton's original statement of his 2nd Law Average versus impulsive force Ex: a skater Ex: Calculate the impulse delivered by the wall MC: Calculate the momentum transfer MC: Rank the forces MC: raindrops Conservation of Linear Momentum N3L: internal forces transfer momentum but cannot change psystem Only external forces can change psystem Discuss: Identify the external forces When is system momentum conserved? totally isolated systems (no external forces at all) functionally isolated systems (no net external force) Just before/after collisions and explosions (if Δ t ≈ 0 then Δpsystem=0) Collisions totally inelastic collisions (colliding particles stick together) elastic collisions: (both psystem and Esystem are conserved inelastic collisions (psystem is conserved; Esystem is NOT conserved) collisions in 2D and 3D Further Questions MC: catching a ball Oscillations and waves