Chapter 10-Forces
All forces that affect motion.
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Nature of Force
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A force is a push or a pull.
Forces have a strength and
direction.
The net force is all the
forces that are added
together.
Unbalanced forces acting
on an object will change the
object’s motion.
Balanced forces acting on
an object will not change
the object’s motion.
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Newton’s Laws of Motion
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Newton’s First Law of Motion
states that an object at rest will
remain at rest and an object
that is moving at constant
velocity will continue moving at
constant velocity unless acted
upon by an unbalanced force.
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Inertia is the tendency of an
object to resist change in its
motion.
The amount of inertia of an
object depends on its mass.
Law of Inertia
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Newton’s Second Law of Motion
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The net force on an object is
equal to the product of its
acceleration and its mass.
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Force = mass x acceleration
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Force is measured in units
called Newtons.
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One newton equals the force
required to accelerate one
kilogram mass at 1 meter per
second per second.
Acceleration = Force / Mass
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Newton’s Second Law(continued)
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Forces are unbalanced
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This law is dependent on two
variables:
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Net forces
Mass of the object
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As the force applied to an object
increases, the acceleration
increases.
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As the mass of an object
increases, the acceleration
decreases.
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Understanding the law.
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Newton's laws declare loudly that
a net force (an unbalanced force)
causes an acceleration; the
acceleration is in the same
direction as the net force.
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Free-body diagrams are diagrams
used to show the relative
magnitude and direction of all
forces acting upon an object in a
given situation. (diagram on right)
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Magnitude & Direction of Forces
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Vectors are quantities which are
fully described by both a
magnitude and a direction.
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Friction
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Friction is the force that one
surface exerts on another
when the two rub against
each other.
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The strength of the force of
friction depends on two
factors:
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Types of surfaces involved.
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How hard the surfaces
push together.
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Types of Friction
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Types of friction:
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Sliding friction-solid
surfaces slide over each
other.
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Rolling friction-object rolls
over the surface.
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Fluid friction-object moves
through a fluid.
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Gravity
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Gravity is the force that pulls
objects towards Earth.
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Objects free fall when the only
force acting on a falling object is
gravity.
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The law of universal gravitation
states that the force of gravity acts
between all objects in the
universe.
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Weight is a measure of the force
of gravity on an object, and mass
is a measure of the amount of
matter in that object.
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Projectile Motion
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An object that is thrown is a
projectile.
Projectile motion is the
motion of an object that is
thrown horizontally.
Gravity pulls down on an
object that is in projectile
motion.
An object thrown will hit the
ground at the same time
that an object is dropped.
Gravitational acceleration is
9.8 m/s2.
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Air Resistance
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Air resistance is a type of fluid
friction that an object falling
through air experience.
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The greater the surface area of an
object, the greater the air
resistance.
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Terminal velocity is the greatest
velocity that a falling object can
reach.
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Terminal velocity is reached
when the air resistance equals
the force of gravity.
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Newton’s Third Law of Motion
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If one object exerts a force on
another object, then the
second object exerts a force of
equal strength in the opposite
direction on the first object.
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Otherwise, for every force
there is an equal and opposite
reaction force.
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Momentum
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Momentum is the product of
the mass and its velocity.
Momentum = Mass x Velocity
Law of Conservation of
Momentum states that the total
momentum of the objects that
interact does not change.
The total momentum of any
group of objects remains the
same unless outside forces act
on the objects.
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Placing Satellites in Space
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A rocket can rise into the air
because the gases it expels
with a downward force exert an
equal but opposite force on the
rocket.
Satellites orbit the earth in
circular paths because of
centripetal force.
Satellites in orbit around Earth
continually fall toward Earth,
but because Earth is curved
they travel around it.
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Chapter 10 Review Questions
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Which of Newton’s Laws states that an object at rest
will remain at rest and an object in motion at a
constant velocity will continue in motion at a
constant velocity unless acted on by an outside
force?
(First Law)
What are the two factors the friction depends on?
(type of surface & how hard the surfaces push
together)
Which law states that the force of gravity acts
between all objects in the universe?
(The Law of Universal Gravitation)
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Chapter 10 Review Questions
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Which of Newton’s Laws states that force is equal to mass times
acceleration?
(Second Law)
What are the three types of friction?
(sliding, rolling & fluid)
Which law states that the total momentum of the objects that
interact does not change?
(The Law of Conservation of Momentum)
Which type of friction has solid surfaces slide over each other?
(sliding)
What is the formula for calculating acceleration?
(acceleration = force/mass)
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Chapter 10 Review Questions
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Which of Newton’s Laws states that for every force there is an
equal and opposite force?
(Third Law)
Which type of friction is illustrated by traveling on a sled down a
hill?
(sliding)
Which force causes an object to move in a circle?
(centripetal force)
Which type of friction is when an object rolls over a surface?
(rolling)
Which of Newton’s Laws of Motion allows a rocket to be
launched into space?
(Third Law)
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Chapter 10 Review Questions
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What do you call a push or a pull?
(force)
Which type of friction is illustrated by a plane flying?
(fluid)
What is the formula for momentum?
(momentum = mass x velocity)
Which type of friction is when an object moves
through a fluid?
(fluid)
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Chapter 10 Review Questions
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What do we call the tendency of an object to resist
change in its motion?
(inertia)
Which type of friction is illustrated by a bowling ball
traveling down a bowling alley?
(rolling)
What is do we call the greatest velocity of a free
falling object?
(terminal velocity)
How does unbalanced forces affect motion?
(start motion or change speed)
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Chapter 10 Review Questions
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What metric unit is equal to the force required to
accelerate one kilogram of mass at 1 meter per
second per second?
(Newton)
What is the value of gravitational acceleration?
(9.8 m/s2)
What is the motion called when a horizontally thrown
object is pulled down?
(projectile motion)
How does balanced forces affect motion?
(doesn’t change motion)
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Chapter 10 Review Questions
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What do we call the force that one surface exerts on
another when the two rub against each other?
(friction)
What is the formula for calculating weight?
(weight=mass x acceleration due to gravity)
Which object will hit the ground first if dropped from
the same height at the same time, a crumpled sheet
of paper or an uncrumpled sheet of paper?
(crumpled sheet of paper)
What is the formula for calculating force?
(force = mass x acceleration)
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