Transcript patterns of motion and equilibrium - SCIENCE

PATTERNS OF MOTION AND
EQUILIBRIUM
Galileo`s concept of inertia
• Force: is a push or pull. It is
needed to start an object
moving. No force is needed
when it starts moving, just the
force to overcome friction.
• Inertia: the property of things
to resist changes in motion.
So a ball moving horizontally
would move forever if friction
is totally absent.
Concept of inertia
Concept of inertia
• Every material object
possesses inertia: how
much depends on its
amount of matter. The
much matter, the much
inertia (that means it has
more mass)
• When comparing 2
objects, you should
compare the abilities to be
resistant to a change in
motion.
Mass vs Weight
• Mass: quatity of matter in an
object. It`s a measure of inertia
that an object exhibits in response
to any effort made to start it, stop
it, or change its state of motion in
any way. (SI Unit: Kilogram)
• Weight: force upon an object due
to gravity. (SI Unit: Newton) W=m
xg
• Directly proportional to each other.
• Gravitation force: 9.8N
• 1 Kg= 9.8N
Vectors and scalars
• Vector quantity: directed
quantity. It has to be
specified not only by
magnitude (size) but by
direction as well. May be
represented by arrows
Ex: velocity
• Scalar quantity: can be
specified by magnitude
alone. Ex: speed
Adding vectors
• Vectors that are add together are called
component vectors. The sum of
component vectors are called a resultant.
• DO NOT MIX VECTORS!!!!!
Net force
• Objects don`t speed up, slow down or change
direction unless a force acts.
• The NET FORCE is the total force acting on an
object. A combination of forces that changes an
object`s state of motion.
• It is a vector quantity, arrows represented the
direction of the quantity.
The equilibrium rule
• Forces are balanced
• There`s no motion
• Called mechanical equilibrium
Support force
• Called NORMAL force
• The force that
supports an object
against gravity
Dynamic equilibrium
• STATIC equilibrium: when an object is
NOT moving
• DYNAMIC equilibrium: once in motion, if
there is no net force to change the state of
motion, it moves at an unchanging speed.
∑F= 0
Force of friction
• Resistive force that opposes the motion or
attempted motion of an object past
another with which it is in contact.
• For solids, liquids and gases
• ALWAYS in opposite direction to motion
• Ex: air resistance
Force of friction
• Depends on: the kind
of material and how
much surfaces are
pressed together
Types of Friction
•
•
Dry friction:
Static friction: the object has no motion.
Sliding friction: the object moves.
Lubricated friction: Needs a lubricant to
start moving.
• Fluid friction: resistance in liquids.
• Air resistance: resistance of an object to
move in the air.
Instantaneous speed
• The speed at any instant
• Most of the time, it is different than the
average speed
Velocity
• Constant velocity means constant speed and
direction
• Direction in a straight line: no curves
• No change in velocity, means no acceleration
• Works with displacement (net distance)
Motion is relative
• Everything is always moving
• Motion is relative to different objects
Acceleration
• Variation is motion, in velocity
Average acceleration
Acceleration
• Recognizing Acceleration on a Graph
Acceleration can be shown on a graph of
velocity versus time.
Tracks
• Circular Motion: Continuous Acceleration
An object traveling in a circular motion is
always changing its direction. Therefore, its
velocity is always changing, so it is
accelerating.
• The acceleration that occurs in circular
motion is known as centripetal acceleration.
Tracks
• Linear motion: motion along a
straight line.
• It can be uniform, with constant
speed or non uniform with a
variable speed
• An example of linear motion is
that of a ball thrown straight up
and falling back straight down.
• objects not subjected to forces
will continue to move uniformly
in a straight line indefinitely
Tracks
• Parabolic motion: A projectile is an object
upon which the only force is gravity.
Gravity, being a downward force, causes a
projectile to accelerate in the downward
direction.