Because energy, the ability to do work, appears in such a wide variety of
physical systems, there are many different kinds of energy. The division of
energy into different types is somewhat arbitrary, but will prove convenient to recognize two very broad categories. Kinetic energy is energy associated with moving objects, while stored or potential energy is energy waiting to be released. Our intuition tells us that two factors govern the amount of objects' kinetic energy . First, heavy objects have more energy than light ones: a bowling ball going with 10 meters per second ( a very fast sprint) carries a lot more kinetic energy than a golf ball going at the same velocity. Kinetic energy is proportional to mass: double the mass, double the kinetic energy.Second, the faster something is moving, the greater the force it is capable of exerting. A high-speed collision causes more damage than a fender bender in a parking lot. It turns out that an object's kinetic energy increases as the square of its velocity. These ideas lead to the equation for kinetic energy. In words: Kinetic energy equals the mass of the moving object times the square of that object's velocity, multiplied by the constant 1/2. In equation form:
In symbols
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Example Reasoning
: = 1/2 * 4 kg * 100 m 2 /s 2 = 200 kg m 2 /s 2 = 200 J For the baseball traveling at 50 m/s: = 1/2 * 0.25 (kg) * 2500 m 2 /s 2 = 312.5 kg m 2 /s 2 = 312.5 J |
The kind of energy, that could result in the exertion of a force over a distance, but is not doing so, is called Potential Energy . An object that has been lifted above the surface of the earth possesses an amount of gravitational potential energy exactly equal to the total amount of work you would have to do to lift it from the ground for the present position. In words: The gravitational potential energy of any object equals its weight (the force of gravity exerted by the object) times its height above the ground. In equation form:
where g is the acceleration due to gravity at the earth's surface. In symbols:
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Stored energy
Work = weight h
= m g h
Drop box : gravity --> acceleration
At floor level : maximum speed
Kinetic Energy(Energy of motion)
One example of stored energy:
internal energy ==> vibration of molecules
Properties of a substance which depends on the temperature :
Temperature Scale :
Another scale (used mostly in the US) is the Fahrenheit scale. The steam point is defined as 212 0 F and the ice-point is defined as 32 0 F. Since the difference of 180 0 F corresponds to 100 0 C, the conversion between Fahrenheit and Celsius is
A more precise fix point as a reference for the temperature is the triple point of water. At this point, water, water vapor and ice coexist. This point is at 0.01 0 C = 273.16K.
SI Defintion of 1 Kelvin:
Characteristic Temperatures:
Large and small Temperatures:(in Kelvin)
What is the temperature 15F in Celcius and Kelvin?
Most European elementary schools cancel classes when the temperature exceeds 30 degrees Celsius. What is this temperature in Fahrenheit?
Watch the Journey to Absolute Zero
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