Transcript Goal: To understand how Galileo and Newton used experimentation

Goal: To begin to understand
how Newton used theory to
further the fields of physics and
astronomy.
Objectives:
1) To learn about the overview of what
Newton did in his career
2) To learn about inertia
First, a question we will come back
to every week for this first month
• Batman is trapped by the joker in the
center of a frozen lake.
• The ice of this lake has no friction.
• It turns out with no friction you cannot
walk/run
• How will batman save himself? Stay
tuned…
Isaac Newton (1642-1727)
• Newton was the father of theoretical physics!
• Had some mathematical discoveries such as
calculus.
• Created “classical mechanics” – branch of
physics.
• Used a prism to prove that white light was
actually a combination of many colors of light –
lead to his book on optics.
• Came up with his 3 laws of motion.
Newton’s Laws:
• Law 1: Law of Inertia (Inertia means
ability to resist change)
A body in rest stays at rest until acted
upon by an outside force, and a body in
motion remains in motion until acted upon
by an outside force.
What is “force”?
• Force is just the pushing or pulling on
something.
• If you push on a door, that is a force on the
door and by Newton’s first law, that door
now has to change its motion (none) to a
new motion (opening).
Concepts question
• You are in the center of a frozen lake
which has no friction and is completely
smooth and flat.
• Ignore wind resistance.
• You toss out a hockey puck at a speed of
1 mile per hour.
• How fast does the hockey puck go when it
is close to the edge of the lake (assume
the lake is 500 miles across)?
More concepts
• You are in a space craft which is over a
trillion miles from the closest star (so that
means there is very little gravity on you)
traveling at a speed of 2 miles per second.
• If you run out of “gas” so to speak, what
will happen to your spacecraft and why?
• How far do you think you will go before
you stop?
Weight
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One form of force is called “weight”.
Weight is your total downwards force.
In this case it is the earth pulling you down.
Units of weight can be pounds or Newtons.
Note that while your mass is the same anywhere
you go, your weight is not.
• One way to loose weight without loosing any
mass is to move to the equator.
• Since the earth spins there is an outward force –
and this decreases your net downward force,
which decreases your weight.
Moon weight
• The moon has 1/6th the gravity of the
earth.
• If you weighed 180 lbs on earth then how
much would you weigh on the moon?
• If your mass on earth was 80 kg then what
is your mass on the moon?
How do you move something?
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Well, you apply a force.
This force makes it accelerate.
The stronger the force, the faster it accelerates.
If an object is at rest, and you give it a force in
the North direction, what direction will it move?
• If an object is moving North and you give it a
force in the South direction and keep applying
that force for a long time then what will happen
to the object?
Now for a tricky one
• I toss a ball in the North direction (giving it
a force in that direction).
• Gravity pulls down on the ball.
• What will the motion of the ball be like?
Equilibrium
• Note: net force is the sum of all forces.
• To add up forces they have to point in the
same direction.
• Note that up = -down
• I stand on the ground.
• What is the net force on me (hint, is my
velocity changing)?
What force?
• Gravity is pulling down on me with a force
of about 1000 N.
• What pushes me upwards with a force of
1000 N and what would happen if this
force suddenly went away?
Run away supertanker
• A supertanker has its engines locked in the on position
but is headed for harbor.
• The supertanker’s engines proved force such that there
is a forwards force of 1 million Newtons
• Ten tugboats tie themselves to the supertanker and push
their engines to the max (100,000 Newtons) in the
opposite direction.
• What is the net force on the supertanker?
• Will the supertanker stop before it runs into the shore?
• We will ignore air and water resistance for this question.
Conclusion
• We have learned that unless an object is
pushed or pulled on, it will keep moving at
a constant speed (and if that speed is 0, it
stays put).
• So, for Batman to get off the frozen lake,
he needs a force – but where oh where
can he get that force from? Is Batman
doomed to stay on that lake forever? Stay
tuned….