Transcript Energy - Madison County Schools

Motion
Observing
To observe an object in motion, you must use
a referenced object. The one sitting still is considered
to be the reference point.
When an object changes position over time, compared
to the reference point, the object is said to be in motion
Motion
Speed
the rate at which an object moves
two variables need to be considered
a. distance
b. time
therefore:
speed = distance
time
Motion
Average speed is a measure of the distance traveled in a given period of time;
it is sometimes referred to as the distance per time ratio. Suppose that during
your trip to school, you traveled a distance of 5 miles and the trip lasted
0.2 hours (12 minutes). The average speed of your car could be determined
as
Motion
Velocity
the speed of an object in a particular direction
velocity always includes a reference point
Motion
Resultant velocity
this calculation is determined as follows
a. if velocity is in the same direction
e.g.
b. if velocity is in opposite directions
e.g.
Motion
Acceleration
is the rate at which velocity changes
to apply a force to an object to make it slow-down,
speed-up or change direction.
To calculate acceleration:
Acceleration = final velocity (m/s) – starting velocity (m/s)
time it takes to change velocity (s)
your answer will be in meter/second
second
Observe the animation of the three cars below. Which car or cars
(red, green, and/or blue) are undergoing an acceleration?
Study each car individually in order to determine the answer.
Now that you've answered the first question correctly, try this one:
which car (red, green, or blue) experiences the greatest acceleration?
As a final test of your understanding, consider the position-time graph at
the right. Each one of the three lines on the position-time graph corresponds
to the motion of one of the three cars. Match the appropriate line to the
particular color of car.
Motion
Force
either a push or a pull; net force
Force in combination
Force in the same direction
Force in different direction
Unbalanced force
produces a change in acceleration
net force is greater than zero
Balanced force
produces no acceleration
net force is zero
Motion
Friction
force that opposes motion between two
surfaces that are touching
hills and valleys
Greater the force, greater the friction
Motion
Gravity
force of attraction between objects that is
due to their masses
note: all matter experiences gravity
in other words
(Gravity sucks; it never spews.)
Motion
Weight
a measure of the gravitational force exerted on
an object
note: weight and mass are different
Gravity and Motion
Motion
all objects fall to the ground at the same rate
What would hit first, elephant or feather?
how? difference in force is canceled by the difference in mass
Motion
Accelerate at constant rate
all objects accelerate toward the ground at
the same rate
the rate or velocity is 9.8 m/s
s
remember: we are not talking
about distance
Motion
Air resistance slows down acceleration
air resistance continues to increase until it matches
the downward force of gravity
object then falls at a constant velocity
called terminal velocity
Motion
Another example of terminal velocity
Remember, the increase in air resistance continues
till it is even with gravity
Motion
Free fall
no air resistance
can only occur in a vacuum
the only force acting is gravity
Motion
Orbiting
created by forward and gravitational forces
occurs when an object is circling around another object
Motion
less than 8000 m/s
less than 8000 m/s
equal to 8000 m/s
greater than 8000 m/s
Motion
Newton’s Laws of Motion
Three laws that relate forces to the motion of objects
First law aka. law of inertia
An object at rest tends to stay at rest and an
object in motion tends to stay in motion with the
same speed and in the same direction unless acted
upon by an unbalanced force.
Motion
Second Law due to unbalanced force
that the acceleration of an object is dependent
upon two variables
a. the net force acting upon the object and
b. the mass of the object
the net force – objects acceleration increases as the
force increases
e.g. shopping cart
mass of the object – objects acceleration decreases
as its mass increases
a=F
m
Motion
Third Law
that for every action (force) in nature,
there is an equal and opposite reaction; force pairs
in other words: if object A exerts a force on object B,
then object B also exerts an equal force on object A
note: we are only talking about forces
Motion
Momentum
property of a moving object that depends
on the object’s mass and velocity
in other words: more momentum an object has the
harder it is to stop the object
Conservation (constant) of momentum
That is, the momentum lost by object 1
is equal to the momentum gained by object 2
Motion
Energy
the ability to do work
remember, work is a transfer of energy so therefore
work only occurs if the force and motion are in the
same direction
Work = F x d; force times distance
since force is in Newtons (N) and distance
is in meters the new label is J or Joules
Motion
Energy of Motion
called kinetic energy
as long as an object is moving there is kinetic energy
kinetic energy depends on mass and velocity
creating work
Motion
Energy of position
called potential energy
gravitational potential energy depends
on weight and height
tells us about stored energy that has the
capacity to do work
Motion
Mechanical energy
kinetic energy + potential energy
as the height decreases the PE also decreases
as the speed increases so does the kinetic energy
Types of energy
Motion
Motion
Conservation of energy
energy can be neither created nor destroyed
total amount of energy in a closed system is always the
same
with conversion of energy you always get thermal energy
what are the energies in the rollercoaster ride?
Motion
Temperature
temperature depends on the kinetic energy
of the particles
as a substance gets hotter, it’s particles moves faster
Motion
Temperature conversion
Motion
Heat
transfer of energy between objects of
different temperatures
energy is transferred from higher temperatures to
lower temperatures
Motion
Types of energy transfer
a. conduction – heat transfer by direct contact
higher kinetic energy to lower
kinetic energy
b. convection – heat transfer by movement
of liquid or gas
c. radiation – heat transfer as
electromagnetic waves