Page 57 - CITS - WCS - Mechanical

WORKSHOP SCIENCE - CITS

Mechanical Equivalent of Heat: Joule’s mechanical equivalent of heat is the amount of work required to produce
1 calorie of heat. According to the first law of thermodynamics, the change in internal energy associated with a
system is equal to the sum of work done by the system and heat added to the system. The potential energy of an
object is due to its position and kinetic energy is due to its motion. The potential energy of an object is zero when
it is in the movement and kinetic energy is zero when the object is in rest. The formula of mechanical energy is.
M.E = K.E + P.E.
Different Temperature measuring scales and their relation
Celsius, Fahrenheit, and Kelvin are the three most popular temperature scales. Thermometers measure
temperature using these three units, using predefined reference points to aid in comparison. Water has a freezing
point of 0 °C and a boiling temperature of 100 °C on the Celsius scale with unit degrees Celsius.
5 different temperature scales?
1 Celsius scale.
2 Kelvin scale.
3 Fahrenheit scale.
4 Rankine scale.
5 Delisle scale.

6 Newton scale.
7 Réaumur scale.
8 Rømer scale.
Transference of heat
Heat transfer, any or all of several kinds of phenomena, considered as mechanisms, that convey energy and
entropy from one location to another. The specific mechanisms are usually referred to as convection, thermal
radiation, and conduction (see thermal conduction). A form of energy pass on through the conduction, convection,
and radiation. Heat transfer occurs any time there is a temperature difference between two objects and occurs in
the direction of decreasing temperature, meaning from a hot object to a cold object.
Conduction, Convection and Radiation
In conduction, heat transfer occurs between objects by direct contact. In convection, the heat transfer takes
within the fluid. In radiation, heat transfer occurs through electromagnetic waves without involving particles. The
heat transfer takes place due to the difference in temperature.
Heat can be transferred in three ways: by conduction, by convection, and by radiation.
Conduction is the transfer of energy from one molecule to another by direct contact. ...
Convection is the movement of heat by a fluid such as water or air. ...
Radiation is the transfer of heat by electromagnetic waves.
A blacksmith heating up a sword in hot coals, and the heat transferring up through the metal
Convection is the mode of heat transfer that is taking place in boiling of water, heat or light from the sun,
microwaves from an oven, X rays from an X-ray tube and gamma rays radioactive elements.
Thermal Expansion
Thermal expansion is where an object expands and becomes larger due to a change in its temperature. A higher
temperature means that the molecules are moving faster on average, causing them to take up more space.
Consequently, objects that are heated up increase in size.
There three types of thermal expansion

Linear thermal expansion.
Areal thermal expansion.
Volume thermal expansion.
Thermal expansion defines the tendency of an object to change its dimension either in length, density, area, or
volume due to heat. Gases expand much more than liquids and liquids expand much more than solids for a given
rise in temperature.

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CITS : WCS - Mechanical - Exercise 3