Efficiency and Mechanical Advantage General Physics – January 26, 2017
MACHINES Machines were invented to make our lives easier! Machines make work easier!
Machines also make some people stupider!
The Six Simple Machines In physics the term “simple machine” means a machine that uses only the forces directly applied and accomplishes its task with a single motion.
Machines can be graded, just like students!
EFFICIENCY Efficiency is the comparison of the amount of work put into the machine to how much work comes out. Quick review: WORK = FORCE × DISTANCE In a perfect machine (with no loss of work due to friction), the efficiency would be equal to 100% HOWEVER, because there is friction the efficiency of any machine is always less than 100%
EFFICIENCY FORMULA OR: Pulley Example Problem
Block and Tackle Problem A block and tackle is used to lift a 200 Newton output- load an output- distance of 3.25 meters. It takes an input-force of 100 Newtons pulling over an input- distance of 12 meters to move it. A. Find the input work. B. Find the output work. C. Find the efficiency
Block and Tackle Problem, answered: A block and tackle is used to lift a 200 N output-load an output- distance of 3.25 m. It takes an input-force of 100 N pulling over an input-distance of 12 m to move it. Find the input work. W = Fd = 100 N × 12 m = 1200 J Find the output work. W = Fd = 200 N × 3.25 m = 650 J Find the efficiency Eff = Output x 100 / Input = 650 J x 100 / 1200 J = 54.2%
Mechanical Advantage Mechanical advantage is the ratio of output force to input force. The higher the MA the better a machine it is! For a typical automotive jack the mechanical advantage is 30 or more. A force of 100 newtons (22.5 pounds) applied to the input arm of the jack produces an output force of 3,000 newtons (675 pounds)— enough to lift one corner of an automobile.
Mechanical Advantage Formula Output force (N) Mechanical advantage MA = Fo Fi Input force (N)
Example #1 A force of 200 Newtons is applied to a machine in order to lift a 1,000 Newton load. What is the mechanical advantage of the machine? MR. G, WHERE ARE THE UNITS FOR MECHANICAL ADVANTAGE?
Example #2 – your turn A force of 500 Newtons is applied to a machine in order to lift a 5000 Newton load. What is the mechanical advantage of the machine?
Example #3 & #4 A machine with a mechanical advantage of 10 is used to produce an output force of 250 Newtons. What input force is applied to this machine? A machine with a mechanical advantage of 2 requires an input force of 120 Newtons. What output force is produced by this machine?
Example #5 A force of 30 Newtons is applied to a machine through a distance of 10 meters. The machine is designed to lift an object to a height of 2 meters. If the total work output for the machine is 18 Newtonmeters, what is the mechanical advantage of the machine? Input force = 30 N output force = work ÷ distance = 18Nm ÷ 2m = 9 N
Example #6 A force of 30 Newtons is applied to a machine through a distance of 10 meters. The machine is designed to lift an object to a height of 2 meters. If the total work output for the machine is 18 Newtonmeters, what is the EFFICIENCY of the machine?
MECHANICAL ADVANTAGE PROBLEMS - PLACE YOUR ANSWERS ON THE HANDOUT! YOUR TURN TO TRY Do & Due TODAY – MECHANICAL ADVANTAGE PROBLEMS - PLACE YOUR ANSWERS ON THE HANDOUT!