Transcript Unit 1 Motion and Forces

CHAPTER 3
Newton’s Second Law of Motion
• F=m×a
• Force = mass ×
acceleration
• The faster you run
into a wall, the more
force you exert on
that wall
• Units are kg×m/s2
• Units are Newtons (N)
F=mxa
• You run into the wall at 50 N of force.
Your mass is 10 kilograms. Calculate your
acceleration.
• Carmine has a mass of 100 g, and he is
running toward you at 2 m/s2. Calculate
the force he will hit you with. (Tricky)
Friction
• Friction is the force that opposes motion
between two surfaces touching each other
• There are 3 types:
• 1. static = not moving
• 2. sliding = pushing a heavy box across
the floor
• 3. rolling = your car spinning its wheels on
the ice
Air Resistance
• Air resistance affects anything moving in
earth’s atmosphere
• The amount depends on the speed, size,
and shape of the object
• Negating air resistance, which will fall
faster: a feather or a bowling ball?
Terminal Velocity
• The force of air resistance increases with
speed
• Remember that the acceleration due to
gravity is always 9.8 m/s2
• When the object is falling so fast that it
cancels the force due to gravity, it is now
at terminal velocity and is no longer
accelerating
• This is the greatest falling velocity possible
Law of Gravitation
• Any two masses exert a gravitational force
on each other
• The size of this force depends on the
mass and the distance between the
objects
• Greater the mass, greater the force
• Closer together, greater the force
Weight vs. Mass
• Weight = mass × acceleration due to
gravity (9.8 m/s2)
• Weight is in Newtons
• Weight is a force
• Mass is in kg
• Mass is the measure of amount of matter
an object contains
Calculating weight
• How much does a person with a mass of
70kg weigh on planet Earth?
• How much does a baby with a mass of
500g weigh on planet Earth? (Tricky)
Projectile Motion
• When you throw a ball on Earth, there are
two forces working on it
• Vertical force pulling down (gravity)
• Horizontal force pushing out (your throw)
Newton’s Third Law of Motion
• For every action there
is an equal and
opposite reaction
• Ex: rocket propulsion
Momentum
• momentum = mass ×
velocity
• p=m×v
• Law of Conservation of
Momentum
• Momentum can be
transferred from one
object to another
• Total momentum of the
system remains the same
Calculating momentum
• Compare the momentums of a 50kg
dolphin swimming 16.4m/s and a 6,300kg
elephant walking 0.11m/s.