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

100%????

Percentage Efficiency Percentage Efficiency of Machines!of Machines!

You will never have a machine that is 100% efficient. Some energy almost always is lost as heat. (Called dissipated)

Machines: Change the size and/or

direction of a force.

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.

Lever:simple machine, bar that turns about a fixed point

(fulcrum)

CrowbarSeesaw

3 types of levers:

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

Which lever arrangement requires the least effort force to raise a 500 N resistance? TAKS-2004

THE END