Download Chapter 10-Forces - Solon City Schools

Chapter 10-Forces
All forces that affect motion.
1
Nature of Force




A force is a push or a
pull.
Forces have a strength
and direction.
Force is measured in
units called newtons.
The net force is all the
forces that are added
together.
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Balanced & Unbalanced Forces


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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What units is force measured in?
:10
grams
joules
kilograms
Newtons
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Newton’s Laws of Motion

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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Newton’s First Law of Motion & Inertia



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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More about Newton’s First Law of
Motion:


The object can be in
motion or moving at a
constant speed.
Outside forces that
affect an object’s
motion:



Gravity
Friction
A brick wall!!!!!!!!!!!!!!!!
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Which forces affect the motion of an
object?
friction
gravity
a immobile barrier
All of the above
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Newton’s Second Law of Motion

The net force on an object is
equal to the product of its
acceleration and its mass.

Force = mass x acceleration

Force is measured in units
called Newtons.


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)

Forces are unbalanced

This law is dependent on two
variables:


Net forces
Mass of the object

As the force applied to an object
increases, the acceleration
increases.

As the mass of an object
increases, the acceleration
decreases.
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Understanding the law.

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.

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

Vectors are quantities which are
fully described by both a
magnitude and a direction.
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What is the mathematical relationship in
Newton’s Second Law of Motion
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F=m/a
F=a/m
F=ma
V=d/t
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What happens to the acceleration as the
force is increased?
:10
Acceleration stays
the same.
Acceleration
increases.
Acceleration
decreases.
Not enough
information is give
to solve this
question.
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Friction

Friction is the force that one
surface exerts on another
when the two rub against
each other.

The strength of the force of
friction depends on two
factors:

Types of surfaces involved.

How hard the surfaces
push together.
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Types of Friction

Types of friction:

Sliding friction-solid
surfaces slide over each
other.

Rolling friction-object rolls
over the surface.

Fluid friction-object moves
through a fluid.
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Which force opposes the motion of two
surface sliding over each other?
:10
Friction
Gravity
Inertia
None of the above
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What type of friction is illustrated by
traveling down a slide on a playground?
Fluid
Rolling
Sliding
None of the above
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Gravity

Gravity is the force that pulls
objects towards Earth.

Objects free fall when the only
force acting on a falling object is
gravity.

The law of universal gravitation
states that the force of gravity acts
between all objects in the
universe.

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

Air resistance is a type of fluid
friction that an object falling
through air experience.

The greater the surface area of an
object, the greater the air
resistance.

Terminal velocity is the greatest
velocity that a falling object can
reach.

Terminal velocity is reached
when the air resistance equals
the force of gravity.
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What is the force of attraction between
every two objects in the universe?
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Friction
Gravity
Inertia
Momentum
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If an object was thrown horizontally and
another object was dropped from the
same height, which would hit the ground
first?
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The one dropped.
The one thrown
Both would be
suspended in the air.
Both would hit the
ground at the same
time.
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Newton’s Third Law of Motion

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.

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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Which of the following laws states that
force is the product of mass and
acceleration?
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Newton’s 1st Law of Motion
Newton’s 2nd Law of Motion
Newton’s 3rd Law of Motion
Newton’s 4th Law of Motion
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Which of the following laws states that for
every force, there is an equal and opposite
force?
1.
Newton’s 1st Law of Motion
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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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