Download CH 13

Chapter 13
Forces
13-1 Nature of Forces
*Force:
push or pull
-gives nrg to an object
-Newton said an object in motion
stays in motion unless acted
upon by an outside force
(1st law of motion)
*Friction:
force that opposes the motion
-sliding friction
*when two solid surfaces slide
over each other
-amount depends on two factors
1. Weight
2. Types of surfaces
-rolling friction
*object rolls over a surface
-oppose motion less than sliding
ex: wheels and ball bearings
-fluid friction
*object moves through a fluid
-all liquids and gases are fluids
-usually opposes motion less than
sliding friction
*Lubricants:
change sliding friction to fluid
friction
-friction can be helpful
ex’s: ????
13-2 Balanced and Unbalanced
Forces
*Balanced forces:
opp in direction and equal in size
-no change in motion
-keeps an object moving at
constant velocity
*Unbalanced force:
not opp and equal
-always cause a change in
motion
13-3 Force and Motion
- 3 laws of motion explain rest,
constant motion, and
accelerated motion
(Isaac Newton)
st
-1
Law of Motion
*Inertia:
tendency of objects to remain in
motion or stay at rest
-object at rest will remain at rest, and
an object in motion will remain in
motion, unless acted on by an
unbalanced force(ex’s)
nd
-2
Law of Motion
- Force = (mass)(acceleration)
N = (kg) (m/s/s)
-unbalanced force accel an object
in the direction of that force
- 1N = 1kg X 1 m/s/s
Rd
-3
Law of Motion
*every action, there is an equal
and opposite rxn
-all forces come in pairs
**Scooter Example**
13-4 Gravity
-Free fall
-All objects accel at the same
rate, regardless of their mass
*Gravity:
attractive force b/all objects in
the universe
-Free fall
~near the surface of earth,
accel due to gravity 9.8m/s/s
-Any falling object meets air
resistance
*Terminal vel:
no longer accel (120mph)
-Projectile Motion
*any object thrown in the air
~is always a curve
-Once you release a ball the only
force acting on it is gravity
Orbital Motion
*object that orbits another object
~it is a result of the object’s
forward inertia and the
downward pull of gravity on the
object
-Newton’s Law of Universal
Gravitation
*all objects in the universe attract
each other by the force of
gravity
-The size of the force depends
on: 1)mass 2)distance b/them
13-5 Weight and Mass
-Weight:
measure of the force of gravity on an
object
~units: newton (N)
~w = m x g
-Mass:
amount of matter
~mass is constant