Post on 22-Dec-2015
I.P.C. 4 D
Investigate and Demonstrate Mechanical Advantage and
Efficiency of various machines such as levers, motors, wheels
and axles, pulleys and ramps
You will never have a machine that is 100% efficient. Some energy almost always is lost as heat. (Called dissipated)
Formula Chart
Constants, Symbols and
Units
Formulas
EFFICIENCYEFFICIENCYToday we will work with the efficiency formula. Find it on
your Formula Chart.
Efficiency- in science it is the amount of work you get out of a system as compared to how much you put into it.
WO
%E WI
When solving a problem---
First read the problem carefully and list what you know and what you are solving for.
Second identify the formula from the formula chart that includes what you are given.
Third Using the triangle method, set up the formula. You may have to rearrange the formula to solve for the unknown quantity.
Calculate !!! What is the efficiency of a machine that requires
110 J of input energy to do 35 J of useful work?
Solving for efficiency…what is the input and output?
Calculate and multiply by 100!
Wo = 35 J
WI = 110 J Wo = 35 J
Efficiency WI = 110 J
E=35J/110J E= .32
Don’t forget to multiply by 100
Efficiency is 32%
÷
What is the efficiency of a machine that requires 110 J of input energy to do 35 J of useful work?
Wo = 100 W
WI = 1000W Wo = 100 J
Efficiency WI = 1000 J
E=100J/1000J E= 0.1
Don’t forget to multiply by 100
Efficiency is 10%
÷
What is the efficiency of her body when a cyclist expends 1000 W of power to deliver mechanical energy to the bicycle at the rate of 100 W?
FOLDABLE TIME
Make a Percent Efficiency Foldable(Hint: on the back write the names of some
simple machines and a definition for mechanical advantage.
Mechanical Advantage:the ratio of output force
to input force for a machine.
How much easier and faster a machine makes your work is the mechanical
advantage of that machine. If a machine has a mechanical advantage of 4, it will
produce 4x more force than you put into it.
Pulleys-The MA of a pulley is equal to the number of supporting ropes
What is the Mechanical Advantage for each of the following pulleys?
MA=2 because
there are 2 supporting ropes. It makes it
two times easier to lift the bucket
MA=4 because
there are 4 supporting ropes. It makes it
four times easier to lift the bucket
Mechanical Advantage and Efficiency are NOT the same thing!!
Machines can make make work easier to do but still not ever be 100% efficient. Stairs increase mechanical advantage because they make it easier to climb a slope but they are not 100% efficient.
A lever can multiply forces
No machine can multiply work or energy…. We may put 100 J of work onto a lever but only get 98 J of work out. The lever is said to be 98% efficient.
To find the MA of a lever, divide the effort arm length by the resistance arm length. MA = effort arm length / resistance arm length
10 cm
2 cm
10÷2 = 5x easier to lift 100 kg ball
Effort Arm
Effort or Lift here
The longer the effort arm, the higher the MA or the easier it makes the work seem.
Resistance Arm
Which lever requires the least effort to lift a load?
TAKS-2006
Hint: Look at the length of the effort arm
MA = effort arm length ÷ resistance arm length