Work Power Force And Motion
• Work - Is a force applied to an object and the object moving.
• Units of measurement
• English system - Foot Pounds - Its equal to one pound of force applied to an object through the distance of one foot
• Metric System - Joules - Is the work done by a force of one newton acting through a distance of one meter.
• Power - The Time-Rate of doing work.
• Units of Measurement
• English System - Foot Pounds per second or Horsepower
• Metric System - Joules per second
• Force
• Mechanical Advantage - Changes the amount of force required to move an object.
• Levers - A device used to gain a mechanical advantage. A lever is balanced when the algebraic sum of both moments equals zero.
• Moment - Is the turning force of the lever.
• Fulcrum - Is the pivot point of the lever.
• First Class lever - This type of lever has its fulcrum some where in the middle of the lever. (Seesaw)
• Second Class Lever - This type of lever has its fulcrum at one end of the lever and the force is applied to the opposite end. (Wheel Barrow)
• Third Class Lever - A third class lever is used to move a resistance a greater distance than the effort applied. (Landing gear)
• Inclined Planes - Achieves mechanical advantage by allowing a large resistance to be moved by a small effort over a long distance.
• Pulleys - Common method used to determine the mechanical advantage of a pulley system is to count the number of ropes that move or support a movable pulley. Remember though, that for every foot the resistance moves you must apply effort to two feet of rope.
• Gears - Gears are used to gain mechanical advantage or change direction of motion. To gain mechanical advantage the number of teeth on either the drive gear or the driven gear are varied. Another thing to keep in mind is that the revolution ratio between two gears is the reverse of their teeth ratio.
• Spur Gears - Have their teeth cut straight across their circumference and are used to connect two parallel shafts.
• Beveled Gears- Used when a drive shaft and driven shaft are not parallel to one another.
• Worm Gears - Used when an extreme amount of mechanical advantage is required. Uses a spiral ridge around a shaft for the drive gear with the shafts usually at right angles to one another.
• Planetary Gears - Used when the shaft has to be driven at a different speed then the force applying the rotation. (Propellers used this so that the engines can maintain a high RPM and generate more power.)
• Stress - When an external force acts on a body it is opposed by an internal force called stress. (The English Measurement is Foot Pounds)
• Tension - Describes the forces that tend to pull an object apart.
• Compression - Describes the forces that tend to push an object together.
• Tension and Compression are the two primary sources of stress.
• Torsion - Is applied to a material when it is twisted and is a combination of both tension and compression.
• Bending- Bending is when tension acts on one side and compression acts on the other of a material. (Aircraft Wings)
• Shear - Tries to slice a body apart.
• Strain - Is the deformation of a material due to stress.
• Hook's Law - If strain does not exceed the elastic limit of a body, it is directly proportional to the applied stress.
• Motion
• Newtons Laws
• First Law - A body at rest tends to stay at rest, and a body in motion tends to stay in uniform motion, unless acted upon by an outside force.
• Second law - Acceleration produced in a mass by the addition of a given force is directly proportional to the force and inversely proportional to the mass.
• Third Law - For every action there is an equal and opposite reaction.
• Speed and Velocity - Speed is a rate of motion or the distance an object moves in a given time. Velocity is the rate of motion in a given direction.
• An increase in the rate of motion is called Acceleration and a decrease is called Deceleration.
• Vectors - are mathematical expressions having both magnitude and direction. (Velocity is a vector quantity)
• Circular Motion
• Centrifugal Force - is the force that pulls a spinning object away from the center of its rotation.
• Centripetal Force - is the equal and opposite force requires to hold a weight in a circular path.

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page revision: 2, last edited: 02 Oct 2008 22:46