Chapter 12 Flash Cards 20 index cards
Work When force is exerted on an object causing it to move in the same direction Work = F x D Joule (J) = Nm
Joule The amount of work you do when you apply a force of 1N to move an object 1m. 1N m = 1J
Power The amount of work done on an object in a unit of time Power = Work/Time J/s Unit is the Watt (W)
Machine A device that makes work easier by changing the amount of force you exert, the distance over which you exert the force, or the direction in which you exert the force.
Input Force The force you exert on a machine. Also called effort.
Output Force The force that the machine exerts on an object. Also called resistance.
Input Work The input force times the input distance.
Output Work Output Force x Output Distance Always less than Input Work
Mechanical Advantage The Number of times a machine multiplies your input force. MA = Output Force Input force
Efficiency Compares the output work to the input work. Expressed as a percent. Efficiency = x 100% Output Work Input Work
Inclined Plane A machine that consists of a flat sloped surface. Ex: ramp MA = H L Length of Incline Height of Incline
Wedge A machine that is thick at one end and tapers to a thin edge at the other end. MA = W L Ex: axe, Knife, Teeth length of wedge width of wedge
Screw An inclined plane wrapped around a cylinder. MA increases as the threads get closer together. Ex: jar lid, car jack.
Fulcrum and Lever A lever is a rigid bar that pivots or rotates on a fulcrum. A Fulcrum is a fixed point for a lever to pivot on. Fulcrum Lever
1 st Class Lever A lever that has the fulcrum between the input (effort) and output (resistance) Always changes direction of force. The closer to the resistance, the more it multiplies your force. Ex: crow bar, see-saw, scissors. F E R
2 nd Class Lever A lever that has the output force (resistance) between the input (effort) and fulcrum. Input and output forces are in the same direction. The closer the output is to the fulcrum, the more MA you get. Ex: Door, wheel barrow, nutcracker. F R E
3 rd Class Lever A lever that has the input (effort) between the output (resistance) and the fulcrum. Usually multiplies distance by decreasing the force. Ex: baseball bat, hockey stick, fishing rod. F R E
Wheel and Axle A machine that has two circular or cylindrical objects fastened together that rotate on a common axis. MA = Ex: screwdriver, steering wheel, door knob. radius of the wheel radius of the axle
Pulley A machine made of a grooved wheel with a rope. MA = the number of supporting ropes holding the object. Ex: flagpoles, cranes, sails. 4 supporting ropes ¼ F
Compound Machine A machine that utilizes (makes use of) two or more simple machines. MA is the product (multiply) of the MA of the machines that make it up. Ex: can opener, apple peeler.