Mechanical Advantage Of Machines

09/9/09 General Science

Mechanical Advantage of Machines

Karen M. Abbago

General Science


Mechanical Advantage

The number of times a simple machine will multiply a force

There are two types of mechanical advantages:

a. Theoretical mechanical advantage

b. Actual Mechanical Advantage


Two types of M.A.

• When the machine is not yet used, we can compute for the mechanical advantage.

• We have to take into consideration the distance the effort will move and the distance the load will move.

• The number of times the machine has actually helped in doing work

• We have to know the amount of force put into the machine (effort) and the amount of force the machine produces (load)


Effort

The force applied on

a machine.


Load

The force produced or resistance of a machine


Equations

= force produced = load or resistance

force applied effort

= distance effort moves (dE)

distance load moves (dL)


Efficiency of machines

• No matter how much work we put into the machine( input work) the work done by the machine is (output work) is always less than what you put in.

• It is because friction between the machine parts converts some of the input work into useless heat.

• We depend on machines so we have to better understand how they work.


% Efficiency= work output x 100%

work input

% Efficiency= AMA/TMA

Efficiency Equation


Sample problems on M. A.

• A machine has a mechanical advantage of 5. If a balikbayan box weighing 1000N is to be lifted onto a truck, how much effort is needed?

Given: AMA= 5 R= 1000N

Required: Effort or E=?

Formula: AMA= R

E

Solution: E= 1000N/ 5

E= 200 N

E= R/AMA


Sample problems on M. A. A machine with a TMA of 5 and an AMA of 4 is

used to raise a 10.0 kg balikbayan box by 5.00 m. What is the work input to the machine?

Given: TMA= 5 AMA= 4 m= 10.0 kg

h= 5.0 m

Solution: Win= mgh

= (10.0kg)( 9.8m/s2) (5m)

= 490 J

Efficiency= AMA/ TMA x 100%

= 4/5 x 100%

= 80%


• Efficiency= work output/work input

0.80 = 490 J/ work input

0.80 (work input)=490J

0.80 .80

Work input= 613 J


Make it Easy by Trial1. A machine has a TMA of 6 and an AMA of 4.

What is the efficiency of the machine?2. A machine is 48% efficient and has an M.A. of

3.0 Find its TMA.3. A machine that is 75% efficient lifts a wooden

crate of 750.0N to a height of 3m.The machine’s TMA is 2. Find:a. the applied force or effort needed to raise the crate.b. the work input


REMEMBER!

It always takes a certain amount of work for all machines to overcome friction. This is why all machines are less than 100% efficient.


What should we do to minimize the effects of friction?

Rollers, lubricants or oils, polished surfaces and streamed lined vehicles can reduced the amount of friction.

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Mechanical Advantage Of Machines