Transcript Newton`s Laws of Motion

Newton’s Laws of Motion
Chapter 19 Forces
Section 3 pg 739
Section 4 pg 743
Isaac Newton “The force was with him"
• Born & studied in
England
• One of the most
influential scientists
of all time
• His discoveries of
forces led to his
credit of the
Newton.
Outline of Today’s Lesson
Main Idea: Newton’s Laws of Motion
• First Law of Motion
• Second Law of Motion
• Net Force = Mass X Acceleration
• Third Law of Motion
• Review Notes
• Discuss Homework for next class
Newton’s First Law of Motion
• Also known as The Law of Inertia
• Inertia has a 2 part definition:
Part I: If an object is moving, then it will
continue to move until a force stops it.
Part II: If an object is at rest, then it will
remain at rest until a force moves it.
How does mass effect inertia?
• Mass: the amount of matter in an object. The
measure of mass does NOT change if gravity is not
present.
• Greater Inertia:
The more mass an object has the harder it will be
to move or keep still.
• Less Inertia:
The opposite is true: If an object has less mass,
then it will be easier to move or keep still.
While you look at this…
• Ask yourself, which one has the
greater mass? The lesser mass?
• Also, based on your guesses
about mass, which one has the
greater inertia? Lesser inertia?
• The strength of inertia is directly
proportional to the mass of the
object.
• In other words, what happens to
mass also happens to inertia.
Let’s Review!
• Newton’s First Law of Motion
*The more mass an object has, the
more inertia it will have
*The less mass an object has, the
less inertia it will have
And now, a word from Jimmy Neutron
on the topic of Inertia…
Remember objects with
more mass are always
harder to keep still or
keep moving! This
affects how much inertia
an object has.
Newton’s Second Law of Motion
• Main Idea of this Law: It’s a math problem
• Law States…
Net Force = Mass X Acceleration
Let’s test out this formula…
Ex 1: What is the net force on a 1,000 kg object
accelerating at 3 m/s2?
1: What formula will you use? NF = M X A
2: Plug in the values. NF = (1,000kg)(3 m/s2)
3: Solve! Net Force = 3,000 Newtons
Let’s try another example…
• Ex 2: A car speeds up as it moves along the
road. If a force of 175 N is needed to make
the car accelerate to 25 m/s2. What’s the
car’s mass?
• Formula: Net Force = Mass x Acceleration
• OR Mass = Net Force / Acceleration
• Plug in your values: Mass = 175 N / 25 m/s2
• Divide and your answer is a MASS OF IS 7 kg
Let’s try another
• Calculate the amount of acceleration
needed to move a 25 kilogram statue
with a force of 75 N.
Formula: Acceleration = NF / Mass
Plug in values
A = 75 N / 25 kg
Divide and your answer is A = 3 m/s2
What is cause and effect?
• Cause: This means an action that
happens
• Effect: This is what happens as a
reaction to the cause
• If your good friend beats you at
video games, then you will smack
that person with the nearest
pillow.
• In this case what’s the cause? The
effect?
“ Newton’s Third Law of Motion states
that if one object exerts a force on
another object, then the second
object exerts a force of equal
strength in the opposite direction on
the first object.”
What????
Newton’s Third Law of Motion
• For every action,
there is an equal
but opposite
reaction.
• Forces react to
each other in
opposite ways.
• That’s why this law
is cause and effect!