Weight vs' Mass

1
Weight vs. Mass
mass amount of matter, does not depend on
location of the object in the universe (units
kg) weight force due to gravity, DOES depend
on location of the object in the universe (units
N) Fg m ag Fg weight (N) m mass (kg) ag
9.81 m/s2 (average value on earth) gravity is
smaller at higher altitudes

2
Normal Force
normal force a force that acts on a surface in
a direction perpendicular to the surface symbol
Fn units N

Fn
Fn Fg
Fg
Fn
Fn Fg cosT
Fg
T
3
Introduction to Friction

• static friction force that resists the start of
  motion between 2 surfaces
• symbol Fs units N
• As long as the object does not move, Fs
  -Fapplied
• kinetic friction force that opposes the
  movement of an object over a surface
• symbol Fk units N
• static friction is always GREATER than kinetic
  friction

4
Friction

• Force of friction depends on
• The normal force on the object
• The type of surfaces in contact
• Fk µk Fn
• Fs µs Fn
• Fk or Fs frictional force (N)
• µk or µs coefficient of friction Depends on
  surfaces! (p.138)
• Fn normal force (N)

5
Air Resistance

• friction between air and an object
• depends on objects size, shape, and velocity
• terminal velocity maximum velocity of an
  object, air resistance equals the weight of the
  object

Four Fundamental Forces

• Gravitational forces
• Electromagnetic forces
• Strong nuclear forces
• Weak nuclear forces