High School Part 1 /2 by SSL Technologies Physics Ex-43 Click PART-1 /2 A “simple” machine is a single mechanical device used to perform work more conveniently.

High School

Part 1 /2

by SSL Technologies

Physics Ex-43

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PART-1 /2

A “simple” machine is a single mechanical device used to performwork more conveniently by providing a “mechanical advantage”.The mechanical advantage of a machine does one of two things:

Multiplies force (at the expense of distance) or Multiplies speed (at the expense of force)

The mechanical advantage of a machine is the multiplier of theforce or speed. It is a number (without units) that tells us thenumber of times the machine multiplies a force (or speed).

I. M. A. The ideal mechanical advantage is the mechanical advantage of an ideal machine. In effect, it is the maximum mechanical advantage that a frictionless machine can deliver.

A. M. A. The actual mechanical advantage of a machine is the real mechanical of a machine that has friction

and thus loss of energy as heat and sound. The A.M.A. is always less than the I.M.A.

The lever family

Physics Ex-43

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PART-1

In order for a machine to operate, it must be supplied with energy.Since energy cannot be created (nor destroyed), it is impossible forany machine to put out more energy than is put into the machine.The diagrams below illustrate an example of the energy flow bothin an ideal and in an real (or actual) machine.

The lever family

Physics Ex-43

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PART-1

Efficiency : The efficiency of a machine tells us what percentage of the input energy is “lost” to friction.

Since an ideal machine has no friction (no energy loss), an idealmachine is 100% efficient. However, all real machines have anefficiency of less than 100%. The formula is:

The lever family

Physics Ex-43

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Two Families of Simple Machines

Note that there are two families of simple machines,the lever family and the inclined-plane family.

As illustrated below, each family consists of three typesof simple machines.:

The lever family

Physics Ex-43

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TERMINOLOGY

E The effort force is the force that is applied (often simply referred to as the “effort”).

R The resistance force is the output force (often simply referred to as the “resistance”).

sE The effort distance is the distance through which the effort force acts.

sR The resistance distance is the distance through which the resistance force acts.

The lever family

Physics Ex-43

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THE LEVER

There are three classes of levers known as the 1st class,the 2nd class, and the 3rd class.

As shown below, the difference in each class is the locationof the effort force and the resistance force.

Note : The 3rd class lever multiplies velocity and not force.

Effort distance x effort force = Resistance distance x resistance force

The lever family

Physics Ex-43

PART-1

THE WHEEL AND AXLE

The wheel and axle is a member of the lever family.It consists of a wheel that is fixed to an axle.

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The lever family

Physics Ex-43

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The lever family

THE PULLEY

The third member of the lever family is the pulley. The pulleyconsists of a wheel that is free to rotate. By itself, a pulleychanges the direction of an applied (or effort) force.

By combining two or more pulleys (known as a pulley system),the pulley provides a mechanical advantage.

Physics Ex-43

PART-1

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The lever familyBy inspection, we can determine the mechanical advantageof a pulley (or pulley system) simply by counting the numberof supporting ropes. Note that a rope whose tension is upwards(that is, pulls upwards) is a supporting rope.

A rope whose tension is downwards is a non-supporting rope.In effect, the mechanical advantage equals the number ofsupporting (upward pulling) ropes.

Remember: To find the ideal mechanical advantage of a pulley system, count all the ropes except the rope of the effort force if it is pulling downward (include it only if it’s pulling upward).

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Use g = 10 m/s2 for the Earth’s gravitational

acceleration.

Reminder

Physics Ex-43Question-1

What is the purpose of a simple machine?

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To provide a mechanical advantage by either multiplyingforce or speed.

Physics Ex-43Question-2

Differentiate between an ideal and actual mechanical advantage.

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The ideal mechanical advantage is for an ideal machine (without friction) and thus no energy loss.

The actual mechanical advantage is for a real machine(with friction) and thus with energy loss.

Physics Ex-43Question-3

List the two families of simple machines:

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The lever family and the inclined plane family.

Physics Ex-43Question-4

Draw a diagram that includes the effort distance and resistancedistance of the following simple machines each having an idealmechanical advantage of 5 :

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a) The 1st class lever

Physics Ex-43Question-4

Draw a diagram that includes the effort distance and resistancedistance of the following simple machines each having an idealmechanical advantage of 5 :

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b) The 2nd class lever

Physics Ex-43Question-4

Draw a diagram that includes the effort distance and resistancedistance of the following simple machines each having an idealmechanical advantage of 5 :

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c) The 3rd class lever

Physics Ex-43Question-4

Draw a diagram that includes the effort distance and resistancedistance of the following simple machines each having an idealmechanical advantage of 5 :

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d) The wheel and axle

Physics Ex-43Question-5

Classify the following simple machines as 1st class lever,2nd class lever, 3rd class lever or wheel-and-axle:

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Machine Classification Purpose(multiplies what?)

a) Steering wheel

b) Wheelbarrow

c) Doorknob

d) Crowbar

e) Broom

f) Scissors

g) Beam balance

h) Fish pole

i) Pliers

j) Nutcracker

Machine Classification Purpose(multiplies what?)

a) Steering wheel Wheel and axle Force

b) Wheelbarrow 2nd Class lever Force

c) Doorknob Wheel and axle Force

d) Crowbar 1st Class lever Force

e) Broom 3rd Class lever Speed

f) Scissors 1st Class lever Force

g) Beam balance 1st Class lever Force

h) Fish pole 3rd Class lever Speed

i) Pliers 1st Class lever Force

j) Nutcracker 2nd Class lever Force

Physics Ex-43Question-6

State the ideal mechanical advantage for each pulley system below:

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Included

Excluded

ExcludedExcluded

Included

ExcludedTo determine the ideal

mechanical advantage of a pulley system, count the number

of ropes that pull up.

Remember: Don’t count the last rope if it pulls down!

Physics Ex-43Question-7

Complete the following energy flow diagram for a machinewhich is 65% efficient knowing that the input energy is 5 000 J.

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5 000 J 3 250 J

65% of 5000 J

1 750 J

5000 J – 3250 J

Physics Ex-43Question-8

A single movable pulley is used to lift a 300 N weight.

If the effort force required is 175 N, answer the following:

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What is the effort force (E) ? a)

What is the resistance force (R) ?b)

What is the I.M.A. ?c)

What is the A.M.A. ?d)

What is the percent efficiency ?e)

What percent of the work done is lost ?f)

What becomes of the work lost?g)

175 N (Given)

300 N (Given)

2(By inspection)

1.7

85 %

15 % (100 – 85)

Lost to friction as heat and sound energy.

Physics Ex-43Question-9

Using the pulley system illustrated on the right, a womanapplies a force of 40 N to lift a mass of 10 kg to a heightof 2 m.

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What is the I.M.A. ? a)

What is the effort force (E) ?b)

What is the resistance force (R) ?c)

What is the resistance distance (SR) ?d)

What is the effort distance (SE) ?e)

What is the input work ?f)

What is the output work?g)

How much work is lost to friction ?h)

What is the percent efficiency ?i)

3(By inspection)

40 N (given)

100 N (given)

2 m (given)

6 m

240 J

200 J

40 J (240 J – 200 J)

83.3 %

Physics Ex-43Question-10

A man uses a bar as a lever to lift a 60 kg stone. If the bar is 1.4 mlong and the resistance distance is 20 cm, answer the following:

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What is the resistance distance (SR) ? a)

What is the resistance force (R) ?b)

What is the effort distance (SE) ?c)

What is the effort force (E) ?d)

What is I.M.A. ?e)

20 cm (given)

600 N (given)

120 cm (140 cm – 20 cm)

100 N

6

Physics Ex-43Question-11

In a machine whose efficiency is 80%, an effort force of 50 N actsthrough a distance of 40 cm. If the resistance distance is 10 cm,find:

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The effort distance (SE) a)

The resistance distance (SR)b)

The effort force (E)c)

The resistance force (R)d)

The I.M.A.e)

The A.M.A.f)

The work inputg)

The work outputh)

The work losti)

0.4 m (given)

0.10 m (given)

50 N (given)

160 N

4

3.2

20 J

16 J

4 J

Physics Ex-43Question-12

A single fixed pulley is used to lift a 120 N weighta distance of 2 m (see diagram). If a 150 N effortforce is required, how much work is lost toovercome friction?

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Physics Ex-43

2 (Two ropes pulling up)

Question-13

A mechanic raises a 100 N weight bymeans of the pulley system as shownon the right. Find:

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The I.M.A. a)

The effort force (E).b)

Since the I.M.A. is 2 (by inspection), then the effort forceis half the resistance force.

50 N

Physics Ex-43Question-14

A pulley system consists of four pulleys contains four supportingropes.

If the system has an efficiency of 60%, how much weight can belifted by an effort force of 400 N?

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This means the I.M.A. = 4

Physics Ex-43Question-15

A 300 N weight hangs on the pulleySystem shown on the right.

Assuming the system is frictionless,what effort force must be applied tohold the mass in equilibrium?

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3

4

I.M.A. = 4

By inspection, we see that the I.M.A. is 4.

This means the effort force is multiplied by 4.

Thus, the effort force is (300 N) ÷ 4.

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