Download Newton`s Second Law

October 28, 2016
Please copy the daily objective onto your drill sheet.
• Today I will be learning about how mass and net
force affect acceleration.
Drill (10.28)
1. Starting from rest a glider is accelerated at a
constant rate by an unbalanced force. What is its
acceleration if it moves 30.0 cm in 0.70 seconds?
2. A college student on the roof of his dorm throws a
water balloon straight downward at a speed of 7.0
m/s. His pal gets drenched precisely 0.800 seconds
later when it hits his head.
A. How fast was the balloon moving when it made contact?
B. How far did the balloon fall?
Board Meeting Prep
You have 1
64
7
8
2 minutes to prepare your
53
board. Make sure it includes:
• Graph of results with correctly labeled axes and a
title indicating the value of what you kept constant
• Mathematical model with appropriate letters for
the IV & DV, and correct units for the coefficient.
• Written explanation of how acceleration depends
on your IV and what you think this relationship
means.
Board meeting agenda
#1 Compare results and try to arrive at a consensus
view of the relationship between DV and IV
#2 Compare the coefficients in your model. How are
they related to the size of what you kept constant?
#3 Discuss limitations. How noisy was your data? Did
you have any outliers?
Consensus?
Acceleration = [constant]/mass
• Acceleration is inversely
proportional to mass
• Larger masses don’t
accelerate as quickly (more
inertia!)
• Units of constant are kg
m/s2 which are equal to
newtons!
• The constant is larger for
bigger masses, in fact…
• The constant matches the
net force!!
acceleration = [constant] x net force
• Acceleration is directly
proportional to net force
• A bigger push changes the
motion faster
• Units of constant are
m/s2/N…but we just
learned N are kg m/s2 so the
units are kg-1
• The constant gets smaller
when the mass gets larger.
In fact…
• The constant equals 1/m!!
Today’s
BIG IDEA . . .
Acceleration is directly proportional to the net force
acting on it and inversely proportional to its mass
a = Fnet/ m
We just discovered Newton’s Second Law of
unbalanced forces!
Wait,
nd
2
Law??
• What was Newton’s First Law again?
Balanced Forces
Constant velocity
An object at rest will remain at rest, and a moving
object will keep moving when there are no
unbalanced forces
Does it make sense?
Is it easier to speed
up, turn, or stop a
grocery cart when it is
empty, or when it is
filled up with
groceries?
Things with less mass
have less inertia and it
is easier to change
their motion
EXIT TICKET
1. Inertia is the tendency of an object to continue moving
at a constant ________.
2. Things with more ________ have more inertia and are
more difficult to __________.
3. The rate _____ changes is directly proportional to the
net force, and inversely proportional to the _______.
4. An unbalanced force of 5.0 N causes an object to
accelerate at 0.80 m/s2. What happens to the
acceleration if the force increases to 15.0 N?
5. How much force is required to change the velocity of a
12.0 kg object by 8.0 m/s in 4.0 seconds?