Download Newton`s Second Law of Motion

Newton’s Second Law of
Motion
Force and Acceleration
Chapter 12-2
I. Galileo Developed the
Concept of Acceleration
A. Galileo developed the concepts of
speed, velocity, and acceleration
B. Used experiments with inclined planes
and noticed the speed of balls
changed as they rolled
C. Acceleration= change of velocity/time
D. 3 Types of Acceleration
1. When something GAINS speed it is
accelerating
2. When something slows down it is
decelerating or negative acceleration
3. Acceleration occurs when an object
changes direction
E. Acceleration
1. In 1s we steadily increase velocity
from 30km/h to 35km/h. In the next
second we increase from 35 km/h to
40km/h. What is our acceleration?
F. Acceleration
1. Acceleration is a measure of the
change per second of velocity
2. (meters per second) per second
3. So when the units are m/s2 the 2
means that there are 2 units of time,
NOT that the number is squared
Acceleration
4. Free Fall is when air
resistance does not
affect the motion of a
falling object
5. A freely falling object
gains speed at the rate
of 10 m/s each second
Acceleration

When an object is thrown up it is
moving against gravity it’s speed
changes at 10 m/s per second
II. Force Causes
Acceleration
A. Acceleration is caused by applying
a force
B. Net Force- combination of all forces
that act on an object
C. Acceleration is directly proportional
to the net force: if net force is
doubled acceleration is doubled
D. Direction of acceleration is in
direction of net force
III. Mass is a Measure of
Inertia
A. If the same force is applied to an
empty can and a can filled with rocks,
which will accelerate more?
B. Mass is an indication of an objects
inertia AND a measure of how much
material an object contains
Mass is a Measure of
Inertia
D. Volume is a measure of space in units
such as cubic centimeters, cubic
meters, and liters
E. Weight is a measure of the pull of
gravity
F. Mass and Weight are directly
proportional
Mass is a Measure of
Inertia



SI unit for mass is kilogram (kg)
SI unit for force is Newton (N)
1 kg object has a weight of 9.8 N and
is generally rounded to 10 N
Mass Resists Acceleration



More massive objects are more
difficult to accelerate
Acceleration is inversely proportional
to the mass
More mass means less acceleration
IV. Newton’s Second Law
Links Force, Acceleration,
and Mass
A. Newton’s Second Law states:
The acceleration produced by a net
force on an object is
1. directly proportional to the net force
2. in the same direction as the net
force
3. inversely proportional to the mass
of the object
B. Acceleration= net force/mass
1. a= F/m
2. What is the acceleration of a 1000
kg car pulled by a force of 2000 N?
V. Friction is a Force that
Affects Motion
A. Friction occurs when an object rubs
against something else
1. This is true for all states of matter
B. ALWAYS acts in a direction to oppose
motion
C. Air drag is the upward force on an
object as it falls down through air
D. The surfaces can reduce or increase
friction
E. Inclined surfaces reduce friction
F. No change in motion occurs when
ΣF = 0
VI. Objects in Free Fall
have Equal Acceleration
A.
Free Fall acts on falling objects
1. The only force acting is gravity
2. All other forces, like air drag, are
neglected
B.
Acceleration of Free Fall does not
depend on mass
VII. 2nd Law Explains Why
Objects in Free Fall Have
Equal Acceleration
A. Newton’s 2nd Law says we must consider
not only weight, but also mass when
considering free fall
B. All freely falling objects have the same ratio
of force to mass and undergo the same
acceleration at the same location
C. Acceleration due to gravity
is g
VIII. Equal Acceleration
in Free Fall
A.
Weight of a 1 kg stone at the earth’s
surface is 10 N. What is acceleration
of the stone?
B. Weight of a 10 kg boulder is 100 N.
What is this acceleration?
C. A 5kg bag of sand has a weight of 50
N. When dropped its acceleration is
D. a=50N/5kg=_____m/s2
IX. Acceleration of Fall is
Less When Air Drag Acts
A. Air drag depends on speed and
surface area
B. Increased air drag results in reduced
acceleration
C. When air is present the downward
net force= weight – air drag
D. As an object falls faster and air drag
increases, acceleration gets less and
less.
E. When the net force of the air drag
equals the weight then net force is
zero!
F. Terminal speed is when acceleration
no longer occurs. Terminal velocity is
when we look at speed and direction.