Unit 2 Dynamics

Force: any push/pull on an object

• causes change in motion (start, stop, speed, slow)

• Total net forces affect acceleration

• Force = vector (magnitude and direction considered)

• Field Forces: always exerted

• Internal Forces: neglibale

• External forces: contribute to net force, others

Free Body Diagram

• illustrates external forces of a system

• Length = magnitude

• Direction = direction of applied force

• Any directions, label with symbol

Newton’s First law/ Law of Inertia

• Objects in motion / at rest stay in motion / at rest unless acted on by a net external force

• Equilibrium: forces balanced

• Inertia: an object’s tendency to keep doing what it’s doing

  • More mass = More inertia

Newton’s Second Law

• Net force = Mass x Acceleration

• Newtons = Kgm/s² or Kam/s²

• Atwood Machine

• Modified Atwood Machine

Mass = amount of matter, won’t change based off location

Weight = forge of gravity (W = Fg = mg)

Newton’s Third Law

• Every action has an equal and opposite reaction

Center of Mass: average position of the parts of an object/system with mass taken into account; location where an object/system would balance

• Uniform Density: mass is evenly distributed over entire volume

Friction: resistance to motion when two materials are in contact with each other

• Depends on the nature of the two surfaces (smooth, rough..) and the normal force a surface exerts on the object

• Coefficient of Friction: static (u_s and u_k)

  • no unit

• Static Friction: sufficient enough to prevent motion

  • Static Friction/F_fs <= u_sF_n

  • If friction is greater, than becomes kinetic friction

• Kinetic Friction: motion

  • F_fk = u_kF_n

  • constant

• Rolling Friction: object rotates as it moves

• Air resistance: when an object collides with air molecules

  • Directly depends on object’s shape, size, and speed

  • Continuously increases until F_ar = F_g and acceleration of object = 0 m/s²

Forces Applied at Angles