Download force - Midland ISD

Newton’s Contributions
• Calculus
• Light is composed of
rainbow colors
• Reflecting Telescope
• Laws of Motion
• Theory of
Gravitation
How many are there?
What are they?
3
1) Inertia
2) F=ma
3) Action/Reaction
Newton’s First Law
(law of inertia)
An object at rest tends to stay at rest
and an object in motion tends to stay
in motion unless acted upon by an
unbalanced force.
1st Law
“An object at rest tends to stay at rest unless
acted upon by an unbalanced force”
True or False?
An object that is
not moving, will
not move unless a
force acts on it.
True
An object in motion tends to stay in
motion unless acted upon by an
unbalanced force.
True or False?
Will something
continue moving in
a straight line
unless acted upon
by an unbalanced
force?
ExampleFull cup of coffee in the
cup holder of a car- the
car stops, the cup stops,
the coffee doesn’t.
True
Newton’s First Law =
Law of Inertia
What is the purpose
of seat belts and
headrests?
Answer
Newton’s First Law =
Law of Inertia
What happens
when you hit a curb
or rock while on a
skate board?
Simply put…things tend to keep on
doing what they are already doing.
A question
If the force of gravity disappeared
between the sun and planets…what
type of path would the planets follow?
A question
*Which has more inertia, a big ship or a
little ship?*
*Why are linemen so big in football?*
How does this affect us?
Will an object moving at the same velocity will
continue moving at the same velocity unless
acted upon by an unbalanced force?
Yes
Balanced Force
Equal forces in opposite
directions produce no motion
Or motion with a constant
velocity
Unbalanced Forces
Unequal opposing forces
produce an unbalanced force
causing motion
*Net Force…this is easy*
• The combination of
all forces acting on
an object
• Determines if the
object moves or
remains at rest
What is the net (total)
force?
• 3 Newtons, right
• 100 Newtons, North
If objects in motion tend to stay in
motion, why don’t moving objects keep
moving forever?
Things don’t keep moving forever because
there’s almost always an unbalanced force
acting upon them.
A book sliding across a table slows
down and stops because of the force
of friction.
If you throw a ball upwards it will
eventually slow down and fall
because of the force of gravity.
Newton’s First Law =
law of _______
• MASS is the measure of the
amount of matter in an
object.
• It is measured in Kilograms
*Mass is the measure of
inertia*
Newton’s First Law =
law of inertia
• INERTIA is a property of an
object that describes how
much
______________________
it will resist change to the
motion of the object
• more _____
____
mass means more inertia
Mass vs Weight…easily
confused with each other
• mass is the amount of matter in an
object.
• weight is a measure of the
gravitational pull on an object,
depends on location (planet)
Mass vs Weight…easily
confused with each other
What should it say to make
sense?
What is weight?
W= mg
A weird fact you need to
know
SI unit of force
(weight) is the
Newton
unit- N…capitalized
because it is named
after a person
Weight= mg
= 1 kg-m/s²
Build your own Newton!
My Newton’s name is… and is…
He/she represents…
(Name) looks like…
He/she also has traveled to…
Overall, (name) is…
Day 3
* How much does 5 kg of
candy canes weigh?*
Weight= mg
= 5 kg (9.8 m/s²)
= 49 Newtons
*A woman stands with 2 feet on the
bathroom scale and weighs 300 N*
*What will the scale
read when she lifts
one foot off the
scale?*
300 Newtons
*If you Know N,  9.8 m/s² = mass*
Formula:
mass=Newtons
9.8 m/s²
The mass of a
reindeer that
weighs 900 N is
about…..
a) 900 kg
b) 9 000 kg
c) 90 kg
90 kg
*Where would you have the largest
mass of a rock if it weighed 1 N, on…
a) the moon?
b) the Earth?
c) Jupiter?
Formula:
mass= Newtons
9.8 m/s²
• 1 N/1.6 m/s² =
0.6 kg
• 1 N/9.8 m/s² =
0.1 kg
• 1 N/ 24.5 m/s² =
0.04 kg
Review
• WEIGHT is a measure of the
gravity on the
force of ________
mass of an object
Newtons
• measured in __________
Newton’s Second Law
Force equals
mass times
acceleration.
F = ma
Newton’s Second Law
• Force = Mass x Acceleration
• Force is measured in Newtons
ACCELERATION of GRAVITY(Earth) = 9.8 m/s2
• Weight (force) = mass x gravity (Earth)
Moon’s gravity is 1/6 of the Earth’s
If you weigh 420 Newtons on earth,
what will you weigh on the Moon?
70 Newtons
If your mass is 41.5Kg on Earth
what is your mass on the Moon?
Newton’s Second Law
One rock weighs 5 Newtons.
The other rock weighs 0.5
Newtons. How much more
force will be required to
accelerate the first rock
at the same rate as the
second rock?
Ten times as much
Newton’s Third Law
For every action there is an equal and
opposite reaction.
Newton’s 3rd Law
• For every action there is an equal and
opposite reaction.
Book to
earth
Table to
book
Think about it . . .
What happens if you are standing on a
skateboard or a slippery floor and push against
a wall? You slide in the opposite direction
(away from the wall), because you pushed on
the wall but the wall pushed back on you with
equal and opposite force.
Why does it hurt so much when you stub
your toe? When your toe exerts a force on a
rock, the rock exerts an equal force back on
your toe. The harder you hit your toe against
it, the more force the rock exerts back on your
toe (and the more your toe hurts).
Newton’s Third Law
• A bug with a mass of
5 grams flies into the
windshield of a
moving 1000kg bus.
• Which will have the
most force?
• The bug on the bus
• The bus on the bug
Newton’s Third Law
• The force would be
the same.
• Force (bug)= m x A
• Force (bus)= M x a
Think I look bad?
You should see
the other guy!
Action and Reaction on Different Masses
Consider you and the earth
Action: earth pulls on you
Reaction: you pull on earth
Reaction: road pushes on tire
Action: tire pushes on road
Reaction: gases push on rocket
Action: rocket pushes on gases
Consider hitting a baseball with a bat. If
we call the force applied to the ball by the
bat the action force, identify the reaction
force.
(a) the force applied to the bat by the hands
(b) the force applied to the bat by the ball
(c) the force the ball carries with it in flight
(d) the centrifugal force in the swing
Newton’s 3rd Law
• Suppose you are taking a space
walk near the space shuttle, and
your safety line breaks. How
would you get back to the shuttle?
Newton’s 3rd Law
• The thing to do would be to take one of the tools
from your tool belt and throw it is hard as you
can directly away from the shuttle. Then, with
the help of Newton's second and third laws, you
will accelerate back towards the shuttle. As you
throw the tool, you push against it, causing it to
accelerate. At the same time, by Newton's third
law, the tool is pushing back against you in the
opposite direction, which causes you to
accelerate back towards the shuttle, as desired.
What Laws are represented?
Review
Newton’s First Law:
Objects in motion tend to stay in motion
and objects at rest tend to stay at rest
unless acted upon by an unbalanced force.
Newton’s Second Law:
Force equals mass times acceleration
(F = ma).
Newton’s Third Law:
For every action there is an equal and
opposite reaction.
1stlaw: Homer is large and
has much mass, therefore he
has much inertia. Friction
and gravity oppose his
motion.
2nd law: Homer’s mass x
9.8 m/s/s equals his
weight, which is a force.
3rd law: Homer pushes
against the ground and it
pushes back.