Download Kinetic Energy

Physics
• Work: done ONLY when a force is applied to an object,
and the object moves IN THE SAME DIRECTION OF THE
APPLIED FORCE
• Work is calculated by multiplying the force by the
distance over which the force is applied
Work = force x distance
W = F x d (Newtons x meters)
• The SI unit for work is Joules (J)
• Work is ZERO if an object is not
moving
• If you are pushing a stalled car and
cannot move it, you might exert a lot
of force, but no work is done
• If you move it, even a little, work is
done
• Machines can help us do work, but only some of it is
useful work (work the machine was designed to do)
• Efficiency: the amount of useful work a machine does
• Some work is done when the machine generates heat
or noises, but it isn’t “useful,” it isn’t what the machine
is intended for
• A pulley used on a boat may experience a decrease in
useful work if heat is generated from friction or if the
pulley squeaks
Power
• Power: the rate at which work is done, or
how much work is done in a given amount
of time
Power = work/time
P = W/t
• The SI unit for power is watt (W)
• One watt is the amount of power needed
to do one joule of work in one second
Energy
• Energy: ability to do work
• Energy is ALL around us and exists in many forms
• Whenever work is done, energy is transformed or
transferred from one system to another
• System: a portion of the universe that is chosen for
studying the changes that take place within it
• The SI unit for energy
is Joules (J)
• The same units as work
since work is only
measured when you
use energy to do it
• All types of energy will
be either
• potential or kinetic
Potential Energy (EP)
• Potential Energy (PE): stored energy,
or the energy of position
• EVERYTHING has potential energy –
it is converted into other forms of
energy!
• Gravitational Potential Energy
(GPE): potential energy due to an
object’s height above ground
• Depends on mass and height – Heavier
objects will have more GPE, and items
higher up will have more GPE
GPE = mass x free-fall acceleration x
height
GPE = mgh
g = 9.8m/s2
GPE = m(9.8 m/s2)h
• Kinetic Energy (KE): energy of motion –
the energy an object has because it is
moving
• Things as large as planets and as small as
atoms have kinetic energy
• Once an object begins to move, it has
the ability to do work
• Kinetic energy depends on the mass of
the object, and the rate of acceleration
• Speed matters more than mass, as a small change in
speed produces a large change in kinetic energy
• A speeding car will do more damage because it has higher
kinetic energy
• An apple that is falling at 10 m/s can do more work than an
apple that is falling at 1 m/s
• Atoms and molecules are always moving, so they
have kinetic energy
• The formula for kinetic energy involves a square root,
which matters when solving for speed
• KE = ½ mv2
• SI unit is J
The kinetic energy of a golf ball is measured to be 143.3 J.
If the golf ball has a mass of about 0.047 kg, what is its
speed?
KE = 143.3 J
m = 0.047 kg
v=?
KE = ½ mv2
• 7 forms of energy that fall
under KE or PE
• Mechanical (KE + PE)
• Radiant (light) (KE)
• Sound (KE)
• Chemical (PE)
• Heat (thermal) (KE)
• Electrical (PE)
• Nuclear (PE)
MRS CHEN
• Mechanical Energy: energy associated with the motion
and position of an object, KE + PE in an object that is
used to do work. MOTION.
• A car moving, a ball that has been thrown, a person falling
• Energy that does not affect motion on a large scale is
nonmechanical
• When you eat food the energy stored in it is non-mechanical
energy
• Chemical Energy: Energy that is released or
absorbed by the rearrangement of bonds
between atoms
• Fuels – food, batteries, gasoline
• Nuclear Energy: the movement of particles in
the nucleus of an atom
• Fission and fusion
• This is how the sun gets energy!
• Electrical Energy: energy resulting
from the movement of electrons
across a circuit
• Lightning
• Thermal Energy: the sum of kinetic
energy in all the particles of an object
• Heat energy
• The higher the temperature, the more
thermal energy
• The larger something it, the more
thermal energy it has
• Light Energy: energy produced by
vibrations of charged particles
• Also called electromagnetic energy or
radiant energy
• Visible light, X rays, UV rays, the sun
• Sound Energy: vibrations travelling
through the medium of the sound
• Sound requires a medium (something to
travel through), like a wave
Law of Conservation of Energy
• Energy readily changes form from one type to another,
however, energy cannot be created or destroyed
• When total energy in a system increases, the increase
must be due to energy that enters the system
• For example, if a person on a trampoline bounces higher the
second time, we can conclude their legs did work to add
energy to the bounce
Energy Transformations
• PE can become KE and vice versa
• At the top of a hill, a car has high PE, but it
changes to KE as it rolls down, the KE gets it
up the next hill
• This change isn’t always complete
• If so, balls would always bounce to the same
height and roller coasters would never stop
gliding
• Some mechanical energy (KE + PE) will
change to other forms of energy 
sound or thermal energy, for example
Energy Transformations
• Energy transformations happen ALL AROUND YOU!
• Light energy from the sun is converted to chemical energy
through photosynthesis, and electrical energy through solar
panels
• A TV changes electrical energy into sound and light energy
• A car changes chemical energy (gas) into thermal and
mechanical energy
• Nuclear energy generates thermal and electrical energy
• Potential energy is converted to kinetic energy when you
stretch a rubber band and then release it
• Thermodynamics: study of heat and temperature
and their relation to work and energy
• Thermodynamics explains energy conservation with
the First Law of Thermodynamics: the net change in
energy equals energy transferred as work or heat
• If heat energy is added to a system, some energy
stays in the system and some leaves. The energy that
leaves does work on the area around it, energy that
stays creates an increase in energy of the system.
• If a pot of water is at room temperature and you add
heat to the system:
• 1st, temperature and energy of water increases.
• 2nd, the system releases some energy and it works on
the environment (maybe heating the air around the
water, making the air rise).