Transcript Expedition 3: Fundamental Forces

Expedition 3: Fundamental
Forces
Forces and Laws of Motion
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Goals
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Define force and explain how forces act on matter.
Identify the many forces acting on an object to determine
the net force on the object.
Explore the relationship between force, mass, and
acceleration.
Apply Newton’s Laws of Motion to understand how forces
affect an object’s motion.
Evaluate the impact of forces and motion on society,
technological advances, and the exploration of our
universe.
Expedition 3: Fundamental Forces
• A force is anything, such as a push or pull, that
causes a change in the motion of an object.
Expedition 3: Fundamental Forces
• Force is a vector quantity, so it is described by
both its magnitude and the direction in which
it acts.
Expedition 3: Fundamental Forces
• Force is measured in the SI unit: newton.
Expedition 3: Fundamental Forces
• Net force is the sum of all forces acting on an
object at any given moment.
Expedition 3: Fundamental Forces
• Friction is the force exerted on two touching
surfaces, causing a resistance in motion.
Free-body diagram
• A free-body diagram acts as a map of all the
forces acting on an object in a given situation
• Vector arrows are used to show the
magnitude, or strength, and direction of all
forces in relation to each other.
• http://www.youtube.com/watch?v=hSQM0ho
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Balanced and Unbalanced Forces
• Balanced and Unbalanced Forces
• When the net force applied an object is not
zero, the forces are described as unbalanced.
• Inertia is the tendency of an object to resist
any change in its motion.
Inertia
• All objects resist changes in motion, so all
objects have inertia.
Inertia
• An object that has a small mass, such as a
baseball, can be accelerated by a small force.
Inertia
• But accelerating an object whose mass is
larger, such as a car, requires a much larger
force.
Inertia
• Thus, mass is a
measure of inertia.
• An object whose mass
is small has less
inertia than an object
whose mass is large
does.
Inertia
• Thus, mass is a
measure of inertia.
• An object whose mass
is small has less
inertia than an object
whose mass is large
does.
• http://www.youtube.com/watch?v=0acpJty6s
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• Newton’s First Law
• An object that is
moving will continue
to move with the
same velocity, until
an unbalanced force
acts on it to stop it,
change its speed, or
change its direction.
Newton’s First Law
Newton’s First Law
• This also means that an object that is
motionless will remain motionless unless an
unbalanced force acts on it.
Newton’s First Law
• The Coefficient of friction is the degree of
resistance of a surface.
• The larger the coefficient of friction is
between any two objects, the more force is
required to move the objects and keep them
in motion.
• Static friction acts on objects that are not
moving. Kinetic friction acts on objects that
are in motion.
• Kinetic (moving) friction
can be further broken
down into three basic
types: sliding, rolling,
and fluid.
• More force is usually needed to overcome
static friction than kinetic friction.
• Newton’s Second Law of Motion
• When a force is applied to an object, the
object will accelerate.
Newton’s Second Law
• Newton’s second law: The unbalanced force
acting on an object equals the object’s mass
times its acceleration.
Newton’s Second Law of Motion
• The relationship between force and
acceleration is described in the equation:
force equals an object’s mass multiplied by its
acceleration.
• F=mxa
Newton’s Cannon
• http://waowen.screaming.net/revision/force&
motion/ncananim.htm
• F=mxa
• Force is measured in newtons.
• One newton is the force that gives a mass of
one kilogram an acceleration of one meter per
second squared: 1 N = 1 kg × 1 m/s2
• The pound (lb) is sometimes used as a unit of
force. One newton is equal to 0.225 lb.
Conversely, 1 lb equals 4.45 N.
Mike's car, which weighs 1,000 kg, is out of gas. Mike
is trying to push the car to a gas station, and he makes
the car go 0.05 m/s/s. Using Newton's Second Law,
you can compute how much force Mike is applying to
the car
Mike's car, which weighs 1,000 kg, is out of gas. Mike
is trying to push the car to a gas station, and he makes
the car go 0.05 m/s/s. Using Newton's Second Law,
you can compute how much force Mike is applying to
the car
Answer = 50 newtons
The Force of Gravity
• All objects with mass are attracted to each
other by a type of force called gravitationalforce.
The Force of Gravity
• The magnitude of this force depends on the
mass of the two objects and the distance
between them.
Law of Universal Gravitation
• When the masses are very large, however, the
gravitational force will be strong enough to hold the
planets, stars, and galaxies together.
• The force of gravity
causes objects to
accelerate as they fall.
On Earth, the force of
gravity causes freefalling objects to
accelerate at a constant
rate of about 9.8 m/s2.
This is known as
gravitational
acceleration(g).
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Terminal velocity
• When the only force acting on a falling object
is gravity, that object is said to be in freefall.
• http://www.youtube.com/watch?v=5C5_dOEy
Afk
• http://www.youtube.com/watch?v=5N9t5qOS
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Weight and Mass
• Mass and weight are often confused with each
other. Mass measures the amount of matter
in an object.
• Weight measures the gravitational force
exerted on an object
Weight is measured in newtons.
• For example, a 66 kg
astronaut weighs 66 kg ×
9.8 m/s2 = 650 N (about
150 lb) on Earth.
• On the moon’s surface,
where g is only 1.6 m/s2,
the astronaut would weigh
66 kg × 1.6 m/s2, which
equals only 110 N (about
24 lb).
Newton’s Third Law
• Newton’s third Law of Motion states that for
every action force, there is an equal and
opposite reaction force.
Newton’s Third Law
• When one object exerts a force on a second
object, the second object exerts a force equal
in size and opposite in direction on the first
object.
Newton’s Third Law
• For example when you
kick a soccer ball the
force exerted on the
ball by your foot is
called the action force,
and the force exerted
on your foot by the ball
is called the reaction
force.
Forces always occur in pairs.
• Action and reaction
forces are applied to
different objects.
• These forces are
equal and opposite.
Forces always occur in pairs.
• Action and reaction force pairs are present
even when there is no motion.(EX sitting in a
chair)
Forces in a force pair do not act on the
same object. .
• Newton’s third law states that forces happen
in pairs.
Newton’s Third Law
Newton’s Third Law
Newton’s Third Law
Newtons Third Law
• http://www.youtube.com/watch?v=jO6B0yx3
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Terminal Velocity
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Review
• http://www.youtube.com/watch?v=mn34mnn
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