Chapter 14 Lesson 3 “Mechanical Advantage and Efficiency”

I. Mechanical Advantage A. Def – the # of times a machine multiplies the input force. (MA) B. Pg. 421 – nut cracker C. MA of Force = Output force Input force D. Ideal – MA w/o friction E. MA of Distance = Input Distance Output Distance

F. Ex. A carpenter uses a claw hammer to pull a nail from a board. The nail has a resistance of 2500 N. The carpenter applies an input force of 125 N. What is the mechanical advantage of the hammer? MA = Output force Input force so… 2500 N 125 N = 20 MA

G. Ex. A worker applies an input force of 20 N to pry open a window that has a output force of 500 N. What is the mechanical advantage of the crowbar? 500 / 20 = 25

H. Find the input force needed to lift a 2000 N rock, using a jack with a mechanical advantage of 10. F i = F o / MA =2000 / 10 =200 N

II. Efficiency B. Def – How much work put into the machine is changed to useful work put out by the machine. 1. Formula Efficiency = W output W input X 100

2. Why doesn’t W out = W in ? -friction -dirt -age -bad parts -improper use

3. Ex: A sofa weighing 1000 N must be placed in a truck bed 1.2 m off of the ground. A worker uses a force of 500 N to push the sofa up the inclined plane that has a slope of 3.5 m. What is the efficiency of the inclined plane? F o = F i = D o = D i = 1000 N 500 N 1.2 m 3.5 m

1000 N x 1.2 m 500 N x 3.5 m = 68.6 % efficient

A record setting buck weighing 1205 N is pulled up a ramp to the back of a pick-up with a force of 600 N by a hunter. If the back end of the pick up is 1.2 meters high and the length of the ramp is 3.2 meters, what is the efficiency of the ramp? 75.3%