Transcript IPC – Unit 2 - Cloudfront.net

IPC – Unit 2
Newton’s Laws
Newton’s Laws of Motion
Forces change the motion of an object in very specific ways
Sir Isaac Newton (1642-1727) was able to state the Laws that
describe the effects of forces.
Newton’s 1st Law of Motion:
An object at rest tends to stay at rest, and an object in
motion tends to stay in motion, unless acted upon by an
outside force.
Also called the Law of Inertia
Inertia: the tendency for an object to resist its
change in motion.
*** The greater the mass of the object – the greater it’s inertia. ***
Newton’s 2nd Law of Motion:
A force acting on an object tends to accelerate that object
in the direction of the force.
Also called the Law of Acceleration
***
***
The greater the mass the greater the resistance to the
acceleration.
Newton’s 2nd Law of Motion can be expressed
in an equation:
Force = (Mass) x (Acceleration)
F = ma
Units:
F = kg·(m/s2)
m = kg
a = m/s2
Example: What is the force exerted on a
1000 kg car going 15 m/s2?
Problem #1: A weightlifter raises a 150kg
barbell with an acceleration of 4m/s2. How
much force does the weightlifter use to raise
the barbell?
Problem #2: An ice skater lifts his partner
above his head with an acceleration of
3.5m/s2. The skater exerts a force of 225N.
What is the mass of his partner?
Problem #3: The motion of a 12kg object is
opposed by a 30N force of friction. At what
rate does friction slow the object down?
Free Fall:
The acceleration of any object under the sole influence
of gravity.
Characteristics of free fall objects:
• Do not incounter air resistance
• On Earth the acceleration of gravity is a constant
9.8 m/s2
*** Formula for acceleration: a = (vf – vi)/t ***
Example: What is the velocity of a rubber
ball dropped from a building roof after 5
seconds?
Problem #4: A car entering a freeway ramp
accelerates at 9 km/hr/sec from 14km/hr to
50 km/hr. What is the car’s time?
Problem #5: A car’s velocity changes from
80 km/hr to 40 km/hr as it travels up a hill in
10 seconds. What is the car’s acceleration?
Newton’s Third Law of Motion:
For every action there is an equal and opposite reaction.
*** Action/Reaction always happens in pairs!!! ***
Momentum:
Is the product of an objects mass and velocity.
Momentum can be expressed with the
following equation:
Momentum = (mass) x (velocity)
P = m·v
Units:
Momentum = kg·(m/s)
Mass = kg
Velocity = m/s
*** An increase (or decrease) in either mass or velocity ***
will increase (or decrease) momentum
Example: Find the momentum of an 7.2kg
rock that is rolling down a hill with a velocity of
3.0m/sec.
Problem #6: A 166.25 kilogram motorcycle
is moving at a speed of 78.75 m/s. What is
the momentum of the cycle?
Problem #7: A child with a momentum of
200 kg-m/sec has a mass of 20 kg. With
what velocity is the child moving?
Law of Conservation of Momentum:
In the absence of any external forces, the total momentum of
the system never changes.
Characteristics of these types of problems:
• No friction
• No air resistance
• The sum of all initial momentums equals the
sum of all final momentums
Law of Conservation of Momentum as an
equation:
P1 = P2
m1v1 = m2v2
P1 = Momentum of 1st object
m1 = Mass of 1st object
v1 = Velocity of 1st object
P2 = Momentum of 2nd object
m2 = Mass of 2nd object
v2 = Velocity of 2nd object
Example: The queue ball on a pool table has
a mass of 150 grams and a velocity of 10
m/s, it then strikes the 8-ball which is at rest
and transfers all of it’s momentum to the 8ball. If the 8-ball has a mass of 200 grams,
then what is its velocity? What is the
momentum of the 8-ball?
Problem #8: A steel ball with a mass of 150
kg is rolling at a rate of 5m/s. It hits a brass
ball which then has a velocity of 3.5m/s.
What is the mass of the brass ball?
Problem #9: A 1.5 kg pinball with a velocity
of 5 m/s collides with a second pinball with a
mass of 2.5 kg. What is the final velocity of
the second pinball after the collision?