Transcript Monday, January 12

DAILY QUESTION
January 12, 2009/
January 13, 2009
1. What is inertia?
2. What are some examples
of Newton’s First Law in
your daily life?
*** If you answered this
yesterday, please ignore 
Agenda
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1/13/09
Daily Question
Semester 2 Expectations
Ch 11 Section 1 Notes
Assignments:
1. 11-1 Review Wksht due 11/14
Semester 2 Expectations
– New Bentley Certificates (10 points each)
– Be in your seat and working on the Daily
Question when the bell rings. 
– R-E-S-P-E-C-T~ for you, others, and things.
Sir Isaac Newton
1642- 1727
• Scientist and Mathematician
• His accomplishments in mathematics,
optics, and physics laid the foundations for
modern science and revolutionized the
world.
• BrainPop about Newton and his laws
Newton’s First Law
An object at rest remains at rest and an
object in motion maintains its velocity
unless it experiences an unbalanced force.
Sometimes called the “law of inertia”
Inertia
The tendency of an object at rest to remain at rest
Or, if an object is moving, to continue moving at a
constant velocity
• All objects have inertia
• Mass is a measure of inertia
– Softball (smaller mass, has smaller inertia) vs bowling
ball (larger mass, has larger inertia)
Newton’s First Law at Work!
• Egg 1 versus Egg 2
– Spin Egg 1
• gently place your forefinger on the top of the egg to
stop it
• then remove your finger immediately after it stops
• record any observations
– Repeat steps with Egg 2
• record any observations
– Using Newton’s First Law, explain your
observations and predict which egg is raw
and which is hardboiled
Egg 1 versus Egg 2
• The raw egg (Egg 2) should start to turn
again. This is because the motion of the
liquid within the egg is still going; the force
you exerted was not enough to stop both
the inertia of the shell and the inertia of the
liquid inside of it. If you held the egg
longer, enough force would have been
exerted to stop the egg completely.
Newton’s First Law at Work!
• Coin on a Card
– Set an index card over a glass
– Put a coin on top of the card
– Flick the card sideways off the glass
• Record your observations
– Try again, but this time slowly pull the card
sideways
• Record your observations
– Using Newton’s First Law, explain your
observations
Coin on a Card
• When pulled slowly, the coin should not
fall into the glass, it should remain resting
on the card. The force of friction caused
the coin to move sideways with the card.
Newton’s Second Law
The unbalanced force acting on an object
equals the object’s mass times its
acceleration
Force = mass x acceleration
F=ma
Force
• SI Unit of force is the newton (N).
– One newton is the force that can give a mass
of 1 kg an acceleration of 1 m/s2
1 N = 1 kg x 1 m/s2
1 pound (lb) = 4.448 N
1 N = 0.225 lb
Using Newton’s 2nd Law:
Finding Force
Practice: Zookeepers lift a stretcher that
holds a sedated lion. The total mass is 175
kg and the upward acceleration is 0.675 m/s2.
What is the force?
F = ma
F = 175 kg x 0.675 m/s2
F = 115 N
Using Newton’s 2nd Law:
Finding Force
Practice: A baseball accelerates downward
at 9.8 m/s2. If the gravitational force is 1.4
N, what is the baseball’s mass?
F= ma or m = F/a
m = 1.4 N / 9.8 m/s2
m = 0.14 kg