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Grade 9 Unit P.5 – Moments and Levers

Moments and Levers

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Standards19.1Know how a simple machine such as a lever can make work easier and that it has many applications.

Objectives: 1- Know what work is.2- Know how a simple machine such as a lever can make work easier and that it has many applications.

WorkIn everyday language work might be writing an essay or digging a garden. But in science work is done when a force is applied to an object and the object moves in the direction of the force.

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Key WordsFriction االحتكاكWork الشغلPivot نقطة

االرتكازForce القوة

Efficiency الكفاءةMultiplier مضاعف


مجال في الشغل ولكن ، حديقة حفر أو مقال كتابة تكون قد اليومية اللغة في شغل كلمة معنىاخر معنى له جسم الشغل. العلم على قوة تطبق عندما القوة يتم اتجاه في فيتحرك

We measure work in joules (J) or kilojoules (kJ). 1 kJ = 1000 Jجول والكيلو الجول هي الشغل قياس وحدة

Work done = force x distance moved in direction of the force

القوة = المسافة ×الشغل

Example:The lawn mower in Figure 1 is pushed 10 m by force of 6 N. Calculate the work that is done by this mower.

Figure 1.W= FxdW= 6 (N) x 10 (m) = 60 J

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W= Fxd

10m

6N


Figure 2

Transfer energy from one form to another and make our jobs easier.

وتجعل اآلالت آخر إلى شكل من الطاقة أسهل تحول العملWe know that the total amount of energy put into a machine must equal the total amount of energy output. This is the Principle of Conservation of Energy.However, only some of the output energy is useful to us. The rest is wasted energy. This affects the efficiency of the machine.A car is not very efficient. For every 100 joules of chemical energy (petrol) that is put into a car, only 25 joules appear as useful movement energy. The other 75 J are wasted as heat (by-products). It is low-grade energy and we cannot use it.

مدخالت و مجموع أن نعلم الطاقة نحن إنتاج مجموع يساوي أن يجب آلة في هو . الطاقة هذا لنا مفيد هو الناتجة الطاقة من بعض فقط ، ذلك ومع الطاقة على الحفاظ يعتبر . مبدأ الباقي إما

مهدره الجه . طاقة كفاءة على يؤثر ازوهذاThe efficiency calculated by:

Because of FRICTION in a machine there is always some wasted energy. This means the efficiency of a machine is always less than 100%.

. دائما الجهاز كفاءة أن يعني وهذا المهدورة الطاقة بعض دائما هناك اآللة في االحتكاك بسببمن 100أقل ٪

Example (1): 4

Efficiency = Useful work output

Work output


An athlete in a race exerts a force of 80 Newton for a distance of 100 meters, while he uses up 40 000 joules of food energy. What is her efficiency?

مقدارها قوة تبذل سباق في لمسافة 80 رياضية تستهلك 100نيوتن أنها حين في ، 000متر الغذائية 40 الطاقة من كفاءتها؟ . جول هي ما

Useful energy = work done= force x distance moved =80 N x 100m = 8000joules

Efficiency = Useful energy output Total energy output

= 8000 / 40 000 = 0.2 x 100 = 20%

Figure 3

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Wasted as heat

Force Multipliers Distance Multipliers

اآلالتةالبسيط


A lever: is a very common machine, it helps us to do work more easily. . A lever is made up of a bar that is free to turn above a fixed point called pivot.

المحور : رافعة تسمى ثابتة نقطة حول للحركة قابلة صلبة ساق الرافعة ، جدا شائعة آلة هي

Figure 4.The lever above in Figure 4 is a simple machine. When you push down at one end of the lever; the load is lifted at the other end. In this particular case:

The output force is twice the input force. In other words, the lever multiplies the input force by two.

There is a price to pay for gain in force, the output force moves only half the distance of the input force.

Most machines waste energy because of friction and efficiency is always less than 100%.

الشكل في أعاله بسيطة 4الرافعة آلة احدي . هي في ألسفل الضغط ؛ طرفي عند الذراعاآلخر الطرف على يرفع الحمل

اإلدخال قوة ضعف اإلخراج القوة .قوة تضاعف الرافعة إن أخري وبعبارة اإلنتاج وقوة ، القوة في مكاسب تحقيق أجل من دفعه يتعين ثمنا تتحرك هناك

من المسافة اإلدخال . نصف قوة هدر هناك اآلالت معظم أقل في دائما هي والكفاءة االحتكاك بسبب للطاقة

.٪ 100من Here are some examples of simple machines

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Scissors are a force multiplier. The effort force needed is about half the load because it is twice as far from the pivot.

مضاعف للقوة.المقص

الحمولة نصف الجهد . قوة


Worksheet

Simple Machines A jar opener, a type writer and an eggbeater are all machines. Most machines are made up of one or more of the six simple machines. The six simple machines are the lever, pulley, the inclined plane, the wedge, the screw, and the wheel and axle see Figure 5..

البيض مضرب و الكاتبة اآللة ، الجرة آالت و فتاحة كلها . اآلالت بسيطة معظم آالت ست من أكثر أو واحد من الشكل . تتكون 5 انظر

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This jar opener is a force multiplier. The effort is farther away from the pivot..

مضاعف للقوة الفتاحةالمحور عن ابعد . .. الجهد

The human arm is a distance multiplier; A small movement of the muscle causes a large movement of the hand. So the arm can make large, rapid movements- although the force is reduced.

When you push on a pedal, the bicycle moves further forwards than your foot moves downwards- although the forward force is less than the force from your foot. This is also an example of a Distance multiplier.


Figure 5

Complete the following questions:1- People use ------------to make work easier يستخدمون - -----------الناس

العمل لتسهيل2- ٍٍSome of energy you put in a machine is used to overcome-----------------

للتغلب اآللة في تضع التي الطاقة من جزء تستخدم3- You can find the efficiency of a machine by -------------the work output by the work input.

بواسطة اآللة كفاءة حساب ------------- يمكنك4-The efficiency of a machine is always less than-------------------------------------

من أقل دائما اآللة كفاءة5- The fixed point at which a lever turns is called the -------------------------------

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تسمى الرافعة حولها تدور التي الثابتة النقطةDefine the following: التالي عرف

1- Lever----------------------------------------------------------------------------------------------------------------------------------------------------------------------2-Work--------------------------------------------------------------------------------------------------------------------------------------------------------------------------Answer the following questions: التالية األسئلة على اجب

1- What are the six simple machines? ---------------------------------------- ------------------------------------------------------------------------------------------2- Decide whether each of the following machines is a force magnifier OR a distance magnifier : للقوة المكبر هي التالية األجهزة من كل كان إذا قرر

للمسافة مضاعفا أوa) - Bottle opener b) - Nail clippers C) - Door handle 3-How does a lever make the work easier? أسهل العمل جعل للرافعة يمكن كيف

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4-Why the efficiency of a machine is always less 100%?من ل اقل دائما اآللة كفاءة 100 ماذا ٪

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5-What are the two types of simple machine? Give example for each?

لكل؟ مثال أعطي البسيطة؟ اآلالت نوعي هما ما------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Problems

6-A horse with a force of 50 N pulls a car a distance 2m. Calculate the amount

قوته لمسافة 50حصان سيارة يسحب الشغل . متر 2نيوتن ? of work done. احسب

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-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------7-You put 4500J of work into a machine. The work output is 3200J. What is the efficiency of the machine?

وضعت آلة 4500Jإذا الناتج . في الشغل اآللة؟ . 3200Jوكان كفاءة هو ما

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9- Make a poster. Collect photographs or drawing of simple machines . Glue each of the examples to a piece of poster board . Label each examples with its common name and the kind of simple machine it is .

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