Transcript Newton`s Laws

Newton’s Laws
But First…
* STORY TIME ABOUT ISAAC NEWTON
Please CORRECT ON YOUR
ENGINEERING NOTES
• Problem: Build a vehicle that moves
forward by pushing backwards (Newton’s
3rd Law) & accounts for Newton’s 1st & 2nd
Laws
• Parameters: Must travel 1.5 meters
forward using Newton’s 3rd law
Newtons 1st law
• What does Newton’s
First Law (The Law of
Inertia) state?
• An object at rest will
remain at rest, and
an object in motion
will continue in
motion at a constant
velocity unless acted
upon by a outside
force.
• What is inertia?
Inertia is the resistance
to change in motion.
The greater the
mass, the greater the
inertia
Demonstration
• EGG MAN IN THE CAR GOING DOWN A
RAMP
Lets try the table cloth trick
• Try using coins of different mass.
• Try using an empty cup vs. cup with a little
water in it.
• What are some
outside forces that
might act on an object
Wall, Brakes
Gravity
Surface Friction
Air Resistance
Newton’s First Law can be used to
explain why the planets stay in orbit
• What is Newton’s
Second Law of
Motion?
• The net force on an
object is equal to the
product of its
acceleration and mass.
Example 2: As the mass of what is in the
wagon decreases, the same force will
cause a greater acceleration.
Example 1: You would be able to
accelerate a wagon pulling a
certain mass more than your baby
brother/sister because you could
apply a greater force.
•Force (N) = Mass x Acceleration
Everyone knows that heavier objects require more
force to move the same distance as lighter objects.
More mass means more force needed to accelerate.
• Ouch!
• Fun!
F= M X A
• How can you increase • You can increase
acceleration?
acceleration by
increasing the force;
decreasing the
mass; or both.
Sample Problem
Answer this on the same page as your
foldable. Show your work!
• Solve: A 52 kg
Water-skier is being
pulled by a
speedboat. The force
causes her to
accelerate at 2m/s2.
Calculate the net
force that causes the
acceleration.
• Force = Mass X
Acceleration
• Force = 52kg X 2m/s2
• Force= 104kg X m/s2
• Force= 104 N
• Related Term:
A bullet has a large
momentum even though
its mass is small because
it has a high velocity.
A baseball moving at
20m/s has less
momentum than a car
moving at 20m/s because
it has less mass.
• MOMENTUM
• A measure of how
hard it is to stop an
object. Objects will
have greater
“momentum” if they
have a larger mass or
velocity.
• Momentum=Mass X Velocity (kgm/s)
• Momentum = Mass x
Velocity
• Sample Problem:
Which has more
momentum: a 3 kg
sledgehammer swung
at 1.5m/s or an 4 kg
sledgehammer swung
at .9m/s?
• Lighter sledgehammer:
3 kg X 1.5 m/s = 4.5 kg*m/s
• Heavier sledgehammer:
4kg X .9 m/s = 3.6 kg*m/s
• Answer: The lighter hammer
has more momentum because
it is swung at a greater
velocity—almost twice as fast.
• What is the law of
conservation of
momentum?
Newton’s Cradle
• The total momentum
of any group of
objects is the same
before and after they
interact unless acted
on by an outside
force.
• What is Newton’s
Third Law of
Motion?
• For every action,
there is an equal (in
size) and opposite
(in direction)
reaction.
• What are some
examples of
Newton’s 3rd law
in nature?
1) A Bird Flying
• Action Force: The bird
pushes the air downward
with its wings.
• Reaction Force: The air
pushes back on those wings
with an equal force that
propels the bird upward.
2) A Squid Swimming
• Action Force: A squid
pushes water back when
swimming
• Reaction Force: The
expelled water pushes
forward with an equal
force and forces the
squid to move ahead.
•
3) A Hammer And A Nail
• Action Force: A hammer
pushes a nail down into the
wood.
• Reaction Force: The nail
pushes back up on the
hammer causing it to come
to a suddenly stop.
• While driving down the
road, an unfortunate bug
strikes the windshield of a
bus. This is a case of
Newton's third law of
motion. The bug hit the
bus and the windshield hit
the bug. Which of the two
forces is greater: the
force on the bug or the
force on the bus?
• Trick Question! Each
force is the same size.
For every action, there is
an equal ... (equal!) and
opposite reaction. The
fact that the bug splatters
only means that with its
smaller mass, it is less
able to withstand the
larger acceleration
resulting from the
interaction.
• What is the equation
for momentum?