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Physics - Concepts - Force, Pressure and Energy

Force, pressure and Energy are some of Physics basic tenets. The following will hopefully serve as a reminder of Physics 101.

Force
Pressure
Energy

Force:

Force is described as what is required to change velocity or acceleration of an objects - recall that acceleration is any change in vector. The formula for force is rather simple:

F = force required, given in Newton's or Dyne's
m = the mass of the object, and
a = acceleration

The Newton (named after Sir Isaac Newton) is the amount required to move 1 kilogram at a distance of 1 meter in 1 second - written as:

The equation of force is Newton's second Law of physics. The three laws are:

  • A body at rest must remain at rest and a body in motion remains in motion unless acted upon by an external force

  • A force (F) on a body (m) gives it an acceleration (a) in the direction on the force, and is inversely proportional to the mass

  • Whenever a body exerts a force from another body, that body exerts a force equal in magnitude and in the opposite direction of the initial mass.

Here is Newton's famous Force equation:

Examples of force: Gravity and Friction

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Pressure:

Pressure is very similar to Force, but applies force over a particular area.

The units of this equation will be:

For comparison, 1 atmosphere (using Earth's atmosphere at sea-level as a standard is:

  • 14.7 lbs/in2

  • 100 kPa

  • 1 bar

  • 760 mm Hg

  • 29.92 inches Hg

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Energy:

Potential Energy (PE) - stored energy as a result of position:
 
 
Kinetic Energy (KE) - energy of motion:
 
 
Energy Units:
  • 1 Joule (J) = Nm
  • 1 erg = dyne cm = 10-7 J
  • 1 calorie = 4.186 J
  • 1 kilocalorie = 1 Calorie (food)

Power:

In order to determine power, we need to determine the value of Work:

  • Angle = 0 degrees if force and work are in same direction
  • Angle = 180 degree is force and work are opposite direction
  • Angle = 90 degrees if force is perpendicular to work

Now we can find Power:

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