Transcript Mechanical & Thermal Energy Energy

Mechanical
&
Thermal Energy
Energy: The ability to do work or
cause change.

Kinetic Energy: energy of motion (KE = ½ mv2)
[m=mass, v=speed]
 ex: ½(5kg∙2m/s2)
½(5∙4)
½(20)
10J
[ J = joules]
K.E. is dependent upon mass & velocity

Potential Energy: stored up energy
(PE = mgh)
 1. Gravitational P.E. – based on position
 2. Elastic P.E. - based on condition
 3. Chemical P.E. - based on composition.
 Energy stored in bonds between atoms is
chemical energy.
Law of Conservation of Energy: Energy
is neither created nor destroyed, it is
only changed or transferred
Energy Conservation examples:



Bouncing ball: Top of the 100 cm drop has 100% GPE
Midway down it has 50% GPE & 50% KE
1 cm from ground it has 99% KE & 1% GPE
When it hits the ground it is 100% EPE, then converts
some to sound & heat energy before bouncing up as KE
The food you eat is chemical potential that your body converts to
heat energy your body uses to make you move (KE)
A roller coaster converts GPE at top of hill to KE as gravity
pulls it down hill speeding it up; however, gravity slows it down
going up hill as KE converts back to GPE. Throughout the
journey the roller coaster slows down & converts KE to thermal
energy due to friction & air resistance.

Heat: movement of thermal energy from a
warmer substance to a cooler substance

Temperature: the measure of the average
kinetic energy of particles in matter

Kinetic Theory of Matter states that all matter is in constant motion.
(motion stops at Absolute Zero: -273 ºC or -460 ºF)

The sum of all kinetic energies of all the particles comprising an
object is thermal energy. (most matter expands as its thermal energy increases)
 The faster molecules are moving, the more thermal energy they have;
which is why balls go farther in warm weather than cold.

Phase changes of matter (solid, liquid, gas, plasma) are caused by
thermal energy transfer, or change in pressure.
Methods of Heat Transfer:
1.
Conduction: heat loss by materials in contact with each other.
(occurs in all matter)
1.
2.


Convection heat loss in fluids where heat rises, pushing
cooler air downward (only occurs in liquids & gases)
Radiation heat loss across a space which requires no medium
to transfer the heat
Conductors are materials that conduct heat well.
Insulators are materials that do not conduct heat well.
Thermal Equilibrium: when objects reach
the same temperature as each other.
Ex: ice water left on cabinet for 2 hours heats to room temp.