Download NEWTON`S 2nd Law of Motion

NEWTON’S
of Motion
nd
2
Law
nd
2
Newton’s
law of
Motion
Describes the relationship of how something with a mass
accelerates when it is pushed/pulled by a force.
Force
Acceleration
nd
2
Newton’s
law of
Motion
An object will accelerate in the direction of a net
force.
Force
Acceleration
Is the direction of the
motion of the object always
the same as the direction of
the acceleration?
50%
50%
1. Yes
2. No
1
2
acceleration
F = ma
mass
Net Force
F= ma Song
Units
F = m·a
2
kg·m/s
=
= Newton
Example
 For a while, the National
Marbles Tournament was,
as one newspaper put it in
1925, "the highest honor
possible in the sporting
world for (kids).” The game
of marbles was a highly
competitive game from the
early 1900’s to late 1960’s in
the United States.
 The game of marbles was
played by propelling a
marble with the thumb to hit
another marble as to drive it
out of a circle.
1950 VFW National
Champ
Tilton "Pork Chop" Holt in
action at the Eaton Rapids,
Michigan finals. From LIFE
Magazine, June 26, 1950
Example (cont.)
 “Pork Chop” Holt flicks .036 kg marble at
an acceleration of 7.2 m/s2. What force
did he use to propel his marble?
 The Inuit people of the Arctic
region, one of the most
forbidding territories on
Earth, have an economy that
revolves around the
changing seasons and the
animals that could be
successfully hunted during
these periods. Assume an
that an Inuit has caught a
sled full of salmon. If he
pulls the sled with a force of
80 N and the sled has a
mass of 87kg, what is the
acceleration of the sled as
he pulls it a short distance
across the snow?
EXAMPLE
Example
 A 15 kg object is being pulled upwards by a
force of 3 N and to the left by 4 N. What is the
objects acceleration?
3N
a=?
m = 15 kg
Fnet = 5 N
4N
a = Fnet / m
= 5 N / 15 kg
= 0.33 m/s2
Application of Newton’s
2nd Law: Weight & mass
Does your mass change on
the moon?
50%
50%
1. Yes
2. No
1
2
How would the size of these forces change on the moon?
How would the size of these forces change on the moon?
WHY?
What things affect weight?
AND
Fw = mg
Weight
(N)
Mass
(kg)
Acceleration
caused by gravity
(m/s2)
What’s your mass?
 Convert pounds into kilograms.
What’s your weight in
Newtons (on the EARTH)?
Fw = mg
9.8 m/s2
Calculate the following using your information:
mass = ____ kg
mass = ____ kg
weight = ____ N
weight = ____ N
mass = ____ kg
weight = ____ lbs
weight = ____ lbs
weight = ____ N
weight = ____ lbs
Earth
g = 9.8 m/s2
Moon
g = 1.6 m/s2
Jupiter
g = 26 m/s2
How does this apply to
falling objects?
A closer look at free-fall
(WITH AIR RESISTANCE)
Air resistance
m = 100 kg
Weight
If force due to air resistance was 400
N, what is the object’s acceleration?
What is happening to the
speed of the previous
object?
33%
33%
33%
1. It is speeding up
2. It is slowing down
3. It is staying the same.
1
2
3
Terminal Velocity
When an object in free-fall is no longer
accelerating
Air resistance
m = 100 kg
Weight
A challenge!
What is the force?
If I drag my book across the table with a 3 N
force at a CONSTANT VELOCITY, what is
the force of friction?
Force of friction = ?
a=
Fnet =
Force pulling = 3 N
What is the force?
If I drag my 1.5 kg book across the table with a
3 N force and it accelerates at a rate of
1.1 m/s2, what is the force of friction?
Force of friction = ?
Force pulling = 3 N
1.5 kg
a = 1.1 m/s2
Fnet =