Transcript Newton`s 3 Laws of Motion

Newton’s 3 Laws of
Motion
Isaac Newton published his most famous book, the
“Mathematical Principles of Natural Philosophy” (also
known as the “Principia”) in 1687 spelling out the key ideas
of classical mechanics. He’s regarded as one of the top
scientists of all time. (along with Einstien, Watson & Crick,
Edison, and Ben & Jerry for developing Cherry Garcia and
Chunky Monkey)
Newton’s Laws
 1st Law: Law of Inertia
 Also called the law of laziness……
 Objects don’t want to change their motion,
they will either stay at rest or move at
constant speed in a straight line UNLESS an
outside Force acts on them.
 An object flying through space at a constant
speed has no force making it move!!!
Newton’s Laws
 2nd Law relating acceleration to a force
 If an object changes its motion (accelerates!)
then it must have an unbalanced Force (or net
Force) acting on it. The amount of acceleration
is directly proportional to the net Force and
inversely proportional to the mass of the
object.
 Accel = Force(net) / mass
Newton’s Laws
 3rd Law: Forces always exist in pairs
 There ain’t no such thing as a force by itself.
Forces are interactions between 2 objects.
 The force on a given object is equal in
magnitude and opposite in direction to the
force on the other object.
 Often referred to as action/reaction (which I
don’t really like)
Newton’s Laws
 What are Forces???
 Forces are typically classified as either
Contact forces of Non-Contact forces
 What’s a contact force?
 What’s a non-contact force?
Forces
 Newton’s 2nd law can also be written
……F = ma
 Looking at the above equation, what are
the units?
 Kg m/s/s ……..this has another name
called a ………………
Forces
 NEWTON!!! (go figure)
Mass vs. Weight
 One of the most common and important
forces we’ll deal with is the force of
gravity.
 The Force of gravity is also known as an
objects Weight……Weight = a Force.
 To calculate the Force of Gravity, multiply
the objects mass x acceleration of gravity
 Or…..Fg = mg where g = 10 m/s/s
Mass vs. Weight
 Fg = mg = Force of gravity
 Mass is measured in kg and is a property of
the material. It’s a measure of an objects inertia
(think of mass and inertia as synonymous)
 You have the same mass on the earth and the
moon, but not the same weight. Your weight on
the moon is 1/6 that on the earth because the
gmoon = 1/6 gearth (where gearth = 10 m/s/s)