Unit 12- Work and Machines

Unit 12- Work and Machines

By S Harris

In science work means a force that is applied through a distance.

• what is important here is that for work to be done on an object, it has to move.​​​

What is work?

Suppose you were to try pushing a door open that says PULL.

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Would this be considered work, even if your arms and hands started to hurt?​ Why or Why not?

Question

No for work to be done the object has to move. You can't move a door that says PULL if you push on it.

Answer

the direction of the force that you ​apply to an object will affect how much work you do on it.​

What is the direction of motion?

• ​you do the maximum amount of work on an object whenever the force and motion are parallel (going in the same direction).

  • in this case work is equal to the force times the distance (W = F x d) the object travels.

Forces that are parallel to the motion​

​You push a refrigerator with a horizontal force of 100 N. If you move the refrigerator a distance of 5 m while you are pushing, how much work do you do?

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Example problem

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​Our Work:

​Work = force X distance

w = _______ x _______ ​

w = _______ ​Joules (j)

​You push a refrigerator with a horizontal force of 100 N. If you move the refrigerator a distance of 5 m while you are pushing, how much work do you do?

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Example problem

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​Our Work:

F = 100 N
d = 5 m




​Work = force X distance

w = __100 N__ x __5 m__ ​

w = _500 Joules (j)

Multiple Choice

a couch is pushed with a horizontal force of 80 N and moves a distance of 5 m across the floor. How much work is done on the moving couch?

• 16 J

• 200 J

• 400 J

• This happens when there is a 90 degree angle between the force and the object's motion

  • they will cancel out.​

  • in this case work will be zero​ (0 J)​

forces that are perpendicular to motion

Machines

a machine is a device that can make work easier by changing the force or motion of an object.

• example:

  • lifting a piano

    • for many people, without the help of some type of pulley system or a ramp.

What's a machine?

• When you use a machine, you apply force to the machine.

  • This force is called the input force.

• The machine then applies force to an object.

  • This force is called the output force.

• The output force may or may not be the same as the input force.

What Else...

• The force that you apply to the machine is applied over a given distance, called the input distance.

• The force applied by the machine to the object is also applied over a distance, called the output distance.

• The output distance may or may not be the

  same as the input distance.

And...

• the machines do NOT increase the AMOUNT OF WORK that you are doing on the object. They ONLY change how the work is done.

  • ​they make it easier to do work by:

    • increasing the force

    • increasing the distance

    • changing the direction

warning!!!

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1. Simple machines

   1. machines that do work with only one movement of the machine

2. Compound machines

   1. machines that are combinations of 2 or more simple machines​

Types of machines

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1. lever

2. pulley (modified lever)

3. wheel and axle (modified lever)

Types of Simple Machines

4. inclined plane

5. screw (modified inclined plane)

6. wedge​ (modified inclined plane)

Examples of compound machines

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1. Is it or is it not work?

2. Work exit ticket

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   https://studiousguy.com/compound-machines-examples/#7_Shovel

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