Newtons Laws 1

1
Newtons Laws (1 2)
2
Newtons 1st Law (Law of Inertia)

• An object at rest will remain at rest,
• An object in motion will continue moving with
  constant velocity (straight line, constant speed)
  
• UNLESS
• An unbalanced (net) force acts on it.

3
Newtons 2nd Law

• When an unbalanced (net) force acts on an object
  of mass m (in kg), the object will accelerate
• Fnet ma

4
What is Fnet?
25 N
5 N
5
What is Fnet?
25 N
35 N
6
What is Fnet?
25 N
25 N
7
What is a?
25 N
25 N
5 kg
8
What is a?
25 N
5 N
5 kg
9
What is a?
30 N
25 N
5 kg
10
Weight

• Weight is the force of gravity acting on an
  object. If the object has a mass m (in kg), the
  weight is
• w mg
• Where g is the acceleration due to gravity (in
  m/s2), and the weight is measured in Newtons (N)

11
Contact force (normal force) FN

• When a surface exerts a contact force on an
  object, that force is perpendicular to the
  surface. Because of this, the force is called
  the normal force.
• Normal line perpendicular line in math

12
Book on table
FN
weight
13
Friction

• On a microscopic level, surfaces are rough and
  jagged

1 nm is one-billionth of a meter ? 0.000000001 m
14
Friction

• Even a perfectly smooth surface is bumpy
  because it is made of spherical atoms think of
  packing oranges in a crate

15
Friction

• Friction is the resistive force caused by the
  microscopic bumps and ridges of two surfaces
  sliding past one another.
• The direction of the friction force always
  opposes the sliding of the surfaces and is
  directed parallel to the surfaces.
• Friction is a force measured in Newtons (N)

16
Friction

• The size (magnitude) of the friction force is
  given by

Where ? is the roughness factor and FN is the
normal force
17
Roughness factor, m

• Depends on the roughness of the two surfaces
  involved determined by experiment
• Static roughness, ms, when surfaces not moving
  past one another
• Kinetic roughness, mk, when surfaces are moving
  past one another

18
Try to push book toward right
FN
Fpush
f
weight