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Chapter 6
Newton’s Second Law of
Motion – Force and
Acceleration
An object accelerates when a net
force acts on it.
Review
Mechanical Equilibrium
Newton’s First Law
Acceleration = Change in velocity /
Time interval
Chapter 12
6.1 Force Causes Acceleration
Unbalanced forces acting on an object
cause the object to accelerate.
Review – Net Force = the vector sum of
the forces.
Acceleration ~ Net Force
Chapter 12
6.2 Mass Resists Acceleration
Review 3.5 – Mass a measure of Inertia
For a constant force, an increase in the
mass will result in a decrease in
acceleration.
Acceleration ~ 1/Mass
(inverse relationship)
Chapter 12
6.3 Newton’s Second Law
Newton’s Second Law states that the
acceleration produce by a net force on an
object is directly proportional to the
magnitude of the net force, is in the
direction of the net force, and is inversely
proportional to the mass of the object.
Chapter 12
6.3 Newton’s Second Law
Acceleration = net force / mass
A = ƩF/ m
(Do not use f. f= frequency)
ƩF = ma
Weight (force due to gravity) = m x g
Chapter 12
6.4 Friction
The force of friction between the surfaces
depends on the kinds of material in
contact and how much the surfaces are
pressed together.
A fluid is a substance that can easily
flow.
Air Resistance is the friction acting on
something moving through air.
Chapter 12
6.4 Friction
A Free-Body Diagram (FBD) is a
diagram showing all the forces acting on
an object.
Chapter 12
6.5 Applying Force - Pressure
For a constant force, an increase in the
area of contact will result in a decrease
in pressure.
Pressure is the amount of force per unit
area.
Pressure = Force / area of application
P=F / A
Chapter 12
6.5 Applying Force - Pressure
Pressure is measured in Newtons per
square meter. Pascal (Pa)
MythBusters – What major physics
principle is ignored in the explanation of
the nail bed demonstration on page (92)?
Chapter 12
6.6 Free Fall Explained
F/m = a = F/m (weight = mg, mg/m=g)
All freely falling objects fall with the
same acceleration because the net force
on an object is only its weight, and the
ratio of weight to mass is the same for all
objects.
Chapter 12
6.7 Falling and Air Resistance
The air resistance force an object
experiences depends on the objects speed
and area.
Air resistance ~ speed x frontal area
Terminal Speed is the speed at which the
acceleration of the falling object is zero
because friction balances the weight.
Terminal Velocity is terminal speed with
direction.
Chapter 12