Motion and Force
• Chapter Twelve: Distance, Time, and Speed
• Chapter Thirteen: Forces
• Chapter Fourteen: Force and Motion
Chapter Fourteen: Force and Motion
• 14.1 Newton’s First and Third Laws
• 14.2 Newton’s Second Law
Investigation 14B
Newton’s Second Law
• What is the relationship between force
and motion?
14.2 Newton’s Second Law
• Acceleration is the rate at which your
velocity (speed with direction) changes.
14.2 Acceleration
•
•
A car can change its
velocity by speeding
up, slowing down, or
turning.
If an object’s
acceleration is zero,
the object could be
moving at a constant
speed in a straight line
or could be stopped.
• To calculate acceleration, you divide the
change in speed by the amount of time it
takes for the change to happen.
14.2 Acceleration
•
•
If an object speeds
up, it has a positive
acceleration.
If it slows down, it
has a negative
acceleration.
What is the acceleration of the sailboat?
14.2 Force, mass and acceleration
• Force causes acceleration, and mass
resists acceleration.
• Newton’s second law relates the force on
an object, the mass of the object, and its
acceleration.
• Force causes acceleration, and mass
resists acceleration.
• The stronger the
force on an
object, the
greater its
acceleration.
– Force is directly
proportional to
acceleration.
– If twice the force
is applied, the
acceleration is
twice as great.
• The greater the
mass, the
smaller the
acceleration for a
given force.
– Mass is inversely
related to force.
– An object with
twice the mass
will have half the
acceleration if
the same force is
applied.
14.2 Applying the second law
•
Keep the following important
ideas in mind:
1. The net force is what causes
acceleration.
2. If there is no acceleration, the net
force must be zero.
3. If there is acceleration, there
must also be a net force.
4. The force unit of newtons is
based on kilograms, meters,
and seconds
14.2 Newton’s second law and
gravity
• Gravitational force exists between all
objects that have mass.
• An object is in free fall if it is accelerating
due to the force of gravity and no other
forces are acting on it.
• Objects in free fall on Earth accelerate
downward at 9.8 m/s2, the acceleration
due to gravity.
14.2 Newton’s second law and
gravity
• An object is in free fall if it is accelerating
due to the force of gravity and no other
forces are acting on it.
• Objects in free fall on Earth accelerate
downward at 9.8 m/s2, the acceleration
due to gravity.
14.2 Universal gravitation
• Gravitational force
exists between all
objects that have
mass.
• You do not notice
gravity between
ordinary objects
because it takes a
huge amount of mass
to create enough force
to notice.
14.2 Universal gravitation
• The force of gravity
between you and
Earth is strong
because the planet’s
mass is huge.
• Newton’s law of
universal gravitation
says the strength of
the force depends on
the mass of the
objects and the
distance between
them.
14.2 Orbital motion
• Newton’s second
law can be used to
explain the motion
of planets, moons,
and satellites in
orbit.
• The orbiting moon
falls around Earth.
Can
kick a soccer
ball
into
orbit?
Can you
we launch
a soccer
ball
into
orbit?
Activity
Making a Spool Car
• Newton’s three laws can be
used to explain the motion
of everyday objects.
• In this activity you will build
a car and apply Newton’s
laws to explain how it
works and why it moves as
it does.