Transcript Forces Review Powerpoint

Forces
and
the Motion
They Influence
A variety of forces are always affecting the
motion of objects around you
Friction
Gravity
Contact/Noncontact
Force
A force is a vector:
With both size and direction
Represent by arrows
right
up
left
down
By using symbols, the action of vectors (forces) on objects
can be read and interpreted.
The length of the vector will show its size and/or
strength.
large
small
Vector can show its impact on an object.
object
Considering the size and direction of all the vectors (forces) acting on
an object allows you to predict changes in the object’s motion.
You give it a try!
The force acting on an
object when all the forces
are combined is the NET
FORCE.
If the net force on an object is
zero, the forces acting on the
object are BALANCED.
A balanced force has the same
effect as no force at all.
A balanced force ceates no
motion or change in an
object’s position.
Only an UNBALANCED
force can change the
motion of an object.
If one player pushes with a
greater force than the other
player, the ball will move in the
direction of the stronger force.
Early Schools of
Thought
•
Ancient Greek thought it was
necessary to apply a
continuous force to keep an
object in motion.
•
Galileo theorized without
friction, a moving object will
continue moving even if there
is no force acting on it.
Mid 1600s
English scientist, Sir Isaac Newton,
studied the effects of forces on
objects and formulated three laws
of motion that are still being used
to help describe and predict the
motion of objects.
Newton’s First Law of Motion
•
Also known as the Law of Inertia
•
Objects at rest remain at rest, objects in motion, remain in
motion with the same velocity (speed and direction) unless
acted upon by an unbalanced force.
Inertia is the resistance of an object to change the speed
or direction of its motion.
Being closely related to mass, when you measure the mass of
an object, you are also measuring its INERTIA.
Newton’s Second Law of Motion
ACCELERATION of an object increases with more force
and decreases with less mass.
The direction in which an object accelerates is the same as
the direction of the force.
The equation Force = mass X acceleration (F = ma) describes
the relationship between force, mass, and acceleration.
NOTE: If you know 2 of the 3 factors, you can rotate the
equation to calculate acceleration.
F = ma
a = F/m
m = F/a
Newton’s Third Law of Motion
Forces always act in pairs
When one object exerts a force on another
object, the second object exerts an equal and
opposite force on the first object. (For every
action, there is complete opposite reaction.)
These force pairs are also known as
Action and Reaction Pairs
A moving object has
a property called
MOMENTUM.
It is a measure of mass
in motion.
• An object’s momentum
is the product of its
mass and its velocity.
•
Momentum is similar to inertia
because it depends on an object’s mass.
Unlike inertia, however, momentum takes
into account how fast the object is moving.
When you drop any object it falls to the ground
faster and faster due to gravity.
Gravity is the force that objects exert on each other due to
their masses.
It is a universal force because it acts on any two masses
anywhere in the universe.
The Force of Gravity
The strength of the gravitational
force between two objects
depends on two factors:
Mass
and
Distance
The Mass of the Objects
Greater mass results in greater force.
•
The more mass two objects have, the more the
force of gravity the masses exert on each other.
•
If one of the object’s mass is doubled, the force of
gravity between the objects is doubled.
The Distance Between the Objects
Greater distance results in smaller force.
As distance between the objects increases, the force of gravity decreases. If
the distance is doubled, the force of gravity is ¼ as strong as before
Gravity on Earth
Gravity acts on both masses
equally, even though the
effects on both masses may be
different.
Acceleration due to Earth’s
gravity is called g .
g = 9.8 m/s2 at Earth’s
surface
Mass and Weight
•
Mass is a measure of how much matter an object contains.
•
It is a property any object has no matter where it is located.
•
A balance is used to measure the mass of an object.
•
Weight is the force of gravity on an object.
•
It depends on the force of gravity acting on that object.
•
A spring scale is used to measure how hard gravity is
pulling on an object.
Gravity keeps
objects in orbit.
Newton hypothesized gravity
pulls objects to the ground
also pulls the Moon around
the Earth.
You can think of an object
orbiting Earth as an object
that is falling around Earth
rather than falling to the
ground.