Energy: Forms and Changes. Nature of Energy. Energy is all around you! You can hear energy as sound. You can see energy as light. And you can feel it as wind. Nature of Energy. Energy is the ability to do work or bring about change. Nature of Energy.
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Energy is the ability to do work or
bring about change.
The sun’s energy is produced from nuclear fusion in which hydrogen nuclei fuse to form helium nuclei.
When you throw a bowling ball, you give it energy. When that bowling ball hits the pins, some of the energy is transferred to the pins.
Thermal and Kinetic
The boulder has
potential energy when
measured from point A
compared to B.
PE = mgh
All PE, no KE
3/4 PE, 1/4 KE
1/2 PE, 1/2 KE
1/4 PE, 3/4 KE
No PE, All KE
Yes! It’s always
10,000 J in this case.
is converted to
relativity have been
proved during solar eclipses.
Light is bent by
GPE = mgh
Roller coasters work because of the energy that is built into the system. Initially, the cars are pulled mechanically up the tallest hill, giving them a great deal of potential energy. From that point, the conversion between potential and kinetic energy powers the cars throughout the entire ride.
At the point of maximum potential energy, the car has minimum kinetic energy.
There is a constant trade off between KE and PE that equals total ME.
Ball slows down
Cartoon courtesy of
Temperature is related to the average kinetic energy of the particles in a substance.
a. K = C + 273 (10C = 283K)
b. C = K – 273 (10K = -263C)
Thermal Energy – the total of all the kinetic and potential energy of all the particles in a substance.
a. As temperature increases, so does thermal energy (because the kinetic energy of the particles increased).
b. Even if the temperature doesn’t change, the thermal energy in a more massive substance is higher (because it is a total measure of energy).
a. The flow of thermal energy from one object to another.
b. Heat always flows from warmer to cooler objects.
Ice gets warmer while hand gets cooler
We know that thermal energy can be transformed or transferred. Now let’s look at just how thermal energy is transferred.
Heat is transferred by conduction, convection or radiation.
heat is transferred by particles touching and transferring kinetic energy to those they touch
the closer the particles (i.e. solids) the better the conduction
both atoms and free electrons can jiggle and jostle and keep the heat transfer going
Convection is the transfer of heat by the movement of the material--gas or liquid particles
Currents are formed at the source of the heat and causes the heated material to rise through the fluid, carrying the heat with it
As the fluid cools, it falls and the process begins again
heat is transferred in matter or space by means of electromagnetic waves that carry energy
waves carrying radiant energy are absorbed by objects and transfer kinetic—thermal—energy to the objects they enter
Some things heat up or cool down faster than others.
Land heats up and cools down faster than water. Why?
The amount of heat required to raise the temperature of one gram of substance by one degree Celsius.
Water molecules form strong bonds with each other; therefore it takes more heat energy to break them. Metals have weak bonds and do not need as much energy to break them.
So check the units in the problem!!!!!
m = 32 g
Ti = 60°C
Tf = 20°C
Q = ?
Cp = 235 J/kg·K
Q = m·T·Cp
m = 32 g = 0.032 kg
T = 20°C - 60°C = – 40°C
Q = (0.032kg)(-40°C)(235J/kg·K)
Q = – 301 J
m = 230 g
Ti = 12°C
Tf = 90°C
Q = ?
Cp= 4184 J/kg·K
Q = m·T·Cp
m = 230 g = 0.23 kg
T = 90°C - 12°C = 78°C
Q = (0.23kg)(78°C)(4184 J/kg·K)
Q = 75,061 J