Download Sliding friction

Motion
Speed
What is Speed?
Speed = distance
time
Speed is the
distance traveled
by a moving
object per unit of
time.
You can calculate the speed of a
moving object by dividing the
distance the object travels by the
time it takes to travel that distance
Speed
Speed that does not change is called constant
speed. But the speed of a moving object is not
always constant. Dividing the total distance by
the total time gives the average speed.
Total Distance = Average Speed
Total Time
Velocity
Velocity is speed in a given direction
One day when Newton was drinking tea in
the garden, he saw an apple fall to the
ground. He started thinking about why it
fell, and finally concluded that the same
force that caused the apple to fall also
kept the moon in orbit around the earth.
This same force also kept the planets in
orbit around the sun.
What is the name of the
force that this famous
scientist described?
GRAVITY
• In other words, the
force of gravity
exists between any
two objects.
• The magnitude
(strength) of the
gravitational force
depends on the
MASS of the objects
and the DISTANCE
between the two
objects.
• The apple incident led Newton to
put forth three laws which explain
why objects move (or don't move)
as they do and these three laws
have become known as:
_ _ _ _ _ _ 's three
LAWS of MOTION
Newton’s First Law
An object at rest stays at rest
And
An object in motion stays in motion
UNLESS
A force acts on it.
What forces do you see acting
on these?
Newton’s
nd
2
Law
An object accelerates, or changes direction,
when a force is applied. Furthermore, the
acceleration due to a force is always in the
direction of the force. When there are
unbalanced forces we know that F=ma.
Acceleration is the change in velocity (that is a
change in speed or direction)
What is the change in this roller coaster?
Newton’s
rd
3
Law
For every action there is an equal and opposite
reaction.
What is the action and reaction
here? Consider friction – which always
opposes motion.
What is a Force?
A push or a pull
Friction effects
motion
Sliding
Rolling
Fluid
Sliding friction
When two solid surfaces
slide over each other the
sliding friction acts
between the surfaces.
When you push a chair
across the floor, sliding
friction opposes your
motion.
Sliding friction
What kinds of things effect the amount
of sliding friction present?
The amount of sliding friction present depends on
two factors: the weight of the object that is
moving and the types of surfaces that the object
slides across. There is more friction when a stack
of cartons is pushed than when just one carton is
pushed. But there is less friction opposing the
motion if the cartons are pushed across a smooth
floor rather than across a carpeted one.
Sliding Friction
Besides “Curling” the
Olympic sport shown
in the previous slide
where else can you
find sliding friction
and is it helpful or a
hindrance?
Rolling friction
Tends to oppose motion less than sliding
friction. So wheels are often placed under
objects to make it easier to use them.
Rolling Friction
Besides Bowling shown
in the previous slide
where else can you
find rolling friction
and is it helpful or a
hindrance?
Fluid friction
All liquids and gases are fluids. Air,
water, and oil are fluids. When an
object moves through a fluid, fluid
friction opposes the motion.
Air resistance is an example of fluid
friction. Substances called lubricants
change sliding friction to fluid friction.
Fluid Friction
Again what examples of
fluid friction can you
think of be specific?
How do we use this
friction to help and
how does it hinder us?
Energy
Kinetic Energy
Potential
Energy
Kinetic Energy
Kinetic Energy is energy of
motion. When you walk, run,
swim and jump, you have
kinetic energy.
Kinetic Energy
The faster an object moves, the
more kinetic energy it has. So
kinetic energy is directly related to
the velocity of an object. In
baseball, a fast ball has more
kinetic energy than a slow curve.
You have more kinetic energy
when you ____________than
when you ____________.
Kinetic Energy
A battleship that is moving at 40km/hr has
much more kinetic energy than a mosquito
moving at the same velocity. So kinetic
energy must depend on something other
than just velocity. The battleship has more
kinetic energy because it has greater mass.
Potential energy
Potential energy is energy stored in an object
due to its position.
Potential energy
Stretch a rubber band between your
thumb and index finger. Keep the
rubber band stretch without any
motion. How long can you hold it
this way? After a short while you
begin to sense the energy in the
rubber band. Yet the rubber band is
not moving! The stretched rubber
band has energy stored in it. You
cannot see this energy, but you know
it is there because the stretched rubber
band can do work as it returns to its
normal shape.
Energy Conversions
Changes in the forms of energy
are called energy conversions.
One of the most common
energy conversion involves the
changing of potential energy to
kinetic energy OR kinetic
energy to potential energy.
Energy Conversion
Can you think of an example of an energy
conversion? Either Kinetic to Potential OR
Potential to Kinetic?
How about in your
Egg Bungee Jump?