linear kinetics

• Mass:

  ·      quantity of matter contained in an object.

  ·      Unit = (m) kg.
• Weight:

  ·      Gravitational force exerted on a body.

  ·      W= m*a(gravity).

  ·      a(gravity)= 9.81

  ·      Unit= Newtons (N)
• Inertia:

  ·      tendency of a body to maintain current state of motion (stationary or moving at a constant velocity).
• Force:

  ·      Push or pull acting on a body to change motion or shape of object.

  ·      Characterized by magnitude, direction, and point of application.

  ·      F=m*a.
• Forces can be:

  ·      Attractive

  ·      Contact

  ·      External

  ·      Internal force
• Law 1= law of inertia:

  ·      Body will maintain a state of rest or constant velocity unless acted on by an external force that changes state.
• Law 2= law of acceleration:

  ·      Force applied to a body causes an acceleration of that body.

  ·      Magnitude of acceleration is proportional to force, in the direction of force and inversely proportional to body’s mass.
• Law 3= law of action and reaction:

  ·      For every reaction, there is an equal and opposite reaction.
• F= u*R

  (u=magnitude is product of the coefficient of friction and the normal reaction force).
• Coefficient of friction= number between 0-1

  • 0 being slippery
  • 1 being rough
• Friction: 

  •   Force action over the area of contact between two surfaces in the direction opposite of motion
  • Quantified by Newtons (N).
  • Acts in accordance with law of reaction.
• Types of friction:

  ·      Maximum static friction (Fm)= maximum amount of friction generated between two static surfaces. (Typically the moment right before it moves)

  ·      Kinetic friction (Fk)= constant-magnitude friction generated between two surfaces in contact during motion (typically when in motion).
• For static bodies:

  ·      Magnitude of friction force = the applied force.

  For dynamic objects:

  ·      Magnitude of friction force remains constantly < maximum static friction.
• Easier to pull than push:

  ·      Pushing adds force towards object (reaction force makes it harder).

  ·      Pulling lifts weight of object to reduce normal force of object.
• Momentum:

  ·      Quantity of motion possessed by a body.

  ·      M= m*v.

  ·      units = kg*m/s
• Conservation of momentum:

  ·      In absence of external forces, total momentum of a given system remains constant.

  ·      M1=M2
• Collison between players of different masses:

  ·      Conservation of momentum= players would tend to continue travelling in direction with the player moving with greater momentum.
• Impulse:

  ·      External forces change momentum in a predictable way.

  ·      Impulse= F*t.
• Momentum-impulse relationship:

  ·      Relationship derived from newton’s law of acceleration.

  ·      Ft= (mvfinal)-(mvintial) therefore Ft= ∆M
• Impact:

  Collision characterised by exchange of large force during a small-time interval
• Types of impacts:

  ·      Perfectly elastic impact= results in conservation of velocity of the system, ( e.g. impact of superball with hard surface).

  ·      Perfectly plastic impact= results in the total loss of system velocity. ( e.g. impact occurs when modelling clay is dropped on a surface).
• Coefficient of restitution:

  ·      Unites number between 0-1 that serves as an index of elasticity for colliding bodies.

  ·      Closer e is to 1= more elastic the impact is.

  ·      -e= = (v1-v2)/(u1-u2).

  ·      Increase in impact velocity and temp= increase in coefficient of restitution.
• Mechanical energy

  Kinetic:

  ·      Energy in motion.

  ·      KE= 1/2*m * v2.

  Potential energy:

  ·      Energy by virtue body position or configuration.

  ·      PE= (wt)(h), PE= (m*a(gravity))*(h (above ground)).
• Conservation of mechanical energy:

  ·      When gravity is only external force acting on body, body’s mechanical energy= constant.

  ·      KE and PE change continuously during projectile motion but will always equal to same value (c).

  ·      KE+PE= constant.
• Principle of work and energy:

  ·      Work of a force= change in energy produced in an object acted on.

  ·      W= ∆KE + ∆PE + ∆TE (thermal energy).