Transcript Motion and forces2

Chapter 2
Force
 Force- push or pull
exerted by one body onto
another
 Not all forces are easily
recognized
 Right now several forces
are acting on all of us.
Balanced forces
 Balanced forces – equal
forces act on an object –
and cancel each other
out
 If the upthrust (or push
up) of the air is equal to
the force of gravity (pull
down), then the balloon
remains suspended in
the air.
Net Force
 Net force – when one
force is greater then
another. This is an
unbalanced force- and
causes an object to
accelerate
 There may be many
force directions in any
one movement
Newton
 Newton’s first law of motion: An object at rest tends to
stay at rest and an object in motion tends to stay in
motion with the same speed and in the same direction
unless acted upon by an unbalanced force
Force
 Force is equal to the
mass of the object times
the objects acceleration.
If any two of these are
known the third can be
found.
 F=mxa
 Mass- kilograms
 a = m/s2
 F = Newtons
Inertia
 Inertia = the resistance
an object has to a
change in its state of
motion – objects with
greater mass have
greater inertia
 Force is not needed to
keep an object in
motion.
 Forces accelerate or
decelerate objects
Friction
Friction- force that
opposes movement
between two surfaces
that are touching
 Causes of friction –
unsmooth surface,
deformations,
molecular attraction
Question
 Imagine a place in the cosmos far from all gravitational
and frictional influences. Suppose that you visit that
place (just suppose) and throw a rock. The rock will
 a. gradually stop.
 b. continue in motion in the same direction at
constant speed.
Gravity
 Gravity is a force that all
matter has on all other
matter.
 Gravity is affected by
mass and distance As mass increases
gravitation increases
 As distance from the
mass increases
gravitation decreases
↑ Einstein’s Theory of General
Relativity
Newton’s Law of Gravitation
Gravity Math
 Near the surface of the
 Your mass is the amount
Earth gravity accelerates
objects at 9.8m/s2
 Weight is the force of
gravity acting on your
body
 Find weight (Newtons)
by multiplying your mass
(kg) by acceleration
(9.8m/s2)
of matter in your body. It
does not change based
on location.
 Your weight can change
depending on the
gravitation of your
location. i.e. the moon