SILO 4.1 (DRAFT)

Year 4, Term 1: Simple machines

Focus: Mechanical advantage Scope and sequence: Forces, Friction, Mechanical advantage

Learning intention: Students identify, explain and demonstrate a variety of contact and non-contact forces.
NSW Syllabus
Australian Curriculum (version 9.0)
“A student investigates the effects of increasing or decreasing the strength of a specific contact or non-contact force.” (ST3-9PW-ST)
"Students learn to identify how forces can be exerted by one object on another and investigate the effect of frictional, gravitational and magnetic forces on the motion of objects." (AC9S4U03)


Introduction to the topic

Simple machines are part of a branch of science known as physics. This video (3:58) provides a really good introduction to physics because it makes connections between science and everything around us.



Rube Goldberg machines

Simple machines

There are generally considered to be six simple machines and many of these have been in use for thousands of years. The six simple machines are:

  1. Levers
  2. Inclined planes
  3. Wedges
  4. Screws
  5. Wheels and axles
  6. Pulleys

https://en.wikipedia.org/wiki/Simple_machine#/media/File:Six_Mechanical_Powers.png

Ask children to write down some examples of simple machines before they watch the video (6:12). This video provides a good overview of all six simple machines and some common applications. 


Mechanical advantage

Mechanical advantage makes work easier. Many of the simple machines are also force multipliers so it is good to understand the subtle difference between mechanical advantage and force multipliers. A helpful step to understand force multiplication is to revise multiplication in relation to numbers as follows:

    When you multiply a number, does it get bigger, smaller or stay the same?

The following Venn diagram shows how all force multipliers provide a mechanical advantage, but not applications of mechanical advantage involve force multiplication.


For example, if you threw a rope over a tree branch to make a simple pulley, this provides a mechanical advantage as you can pull down on the rope or even use your body weight to help apply a downward force. The convenience of being able to pull down on the rope rather than pulling up provides a mechanical advantage but the force itself is not magnified. The most common applications of simple machines involve force multiplication and mechanical advantage.

Levers

This first video (4:46) is titled The mighty mathematics of the lever as it traces the use of levers right back to Archimedes and his boast that he could move the whole world with a gigantic lever.



    Do you think Archimedes was serious about lifting the whole world or was he making a point?

The following video (2:44) provides and overview of the three main classes of levers and a handy way to remember them.


This simulation is a good way to become familiar with first-class levers. The concrete pylons are also useful for making predictions.


Simulation by PhET Interactive Simulations, University of Colorado Boulder, licensed under CC-BY-4.0 (https://phet.colorado.edu).

Pantographs

The following video (2:27) outlines an activity using pantographs.




(Image source: https://en.wikipedia.org/wiki/Pantograph#/media/File:Pantograph_animation.gif)


Wheels and axles

The next type of simple machine we will look at is the WHEEL and AXLE. This video (1:48) provides a good and it is interesting how the narrator encourages us to think of the wheel as a rotating lever.


Can you think of any machines we use in our everyday routine that use a wheel and axle?

Activity:
To understand out how the simple machine of wheel and axle assist in simplifying a task, we are going to test different materials to use in building a wheel and axle and see which works the best!

We are going to split up into groups of 2 or 3, and each group is going to receive a different set of materials to use for their wheels and axles, while all groups will receive the same cardboard piece to act as the body of the car.

In your groups, you will have 20 minutes to design your vehicle using the supplies given. At the end of the allotted time, we will set up the cars, and race them by pushing them down a ramp and seeing which first reaches the finish line, still intact.



  • What did you notice about the different wheels and axles that were used by each group?
  • Which set worked the best and why?
  • What variable – wheel thickness, wheel diameter, axle type, etc. – did you think made the biggest difference in the efficiency of the car, giving it the greatest mechanical advantage?

Pulleys

Pulleys are the next type of simple machine we will look at. Have you wondered how cranes are able to lift such heavy objects to such great heights? It would take a lot of strength to carry block by block in the construction process, so they use PULLEYS to make the job easier!

(Image source: https://pxhere.com/en/photo/172528#google_vignette)

This video (2:27) is a great introduction to pulleys.


The following image is a screenshot from the video which you just watched showing different pulley configurations. The system of two or more pulleys is also known as a block and tackle.

Activity:

As today’s activity, we are going to work in pairs to build each of the above pulley types and test the difference in force required to lift a specific weight. The materials you are going to use are listed below:
  • Wooden board with hooks
  • String 
  • Pulleys 
  • Weights
  • Spring scale
Your task is to build each of the pulley types, attaching the weight to one end and pulling the other end with the spring scale. Note that a spring scale measures the amount of force used to lift an object. FORCE is measured in NEWTONS, just as distance is measured in metres. As you test each pulley type, record the amount of force used in each scenario in the table below.

This table is also available here as an A4 sized PDF.


   What did you notice in your results?

Likely you found that the SYSTEM OF PULLEYS was the pulley type that required the LEAST amount of force. This is because the way pulleys work is by distributing the force along the cables that support them. With more pulleys, there are more ropes and therefore routes for the force to be distributed along.


   Was there anything else specifically different about the two-pulley system that you noticed?

In order to get the pulley to travel the required distance, we had to pull the rope TWICE AS FAR. This is because, though these simple machines provide a MECHANICAL ADVANTAGE, they are not magic. Therefore, in order for us to reduce the amount of force required, something else has to be sacrificed – in this case that is achieving the goal of moving the weight in a short distance.

Note: Some construction sets such as Lego also have pulley pieces where you can make similar configurations as shown below:

Inclined planes


Wedges

 

Screws

The following video (2:40) explains the mechanical advantage of screws and relates this to to other devices such as car jacks.


Revision

There are six different types of simple machines, all used in different capacities by engineers. Can you think of ways these have been used in everyday life?

These machines make a simple task easier to accomplish. For example, take a look at the block below. When faced with the challenge of climbing stairs, there are a number of simple machines that can be employed to help achieve this task.

Wait a minute! Does anyone notice anything about the second two solutions presented for the block?

That’s right, there is more than one simple machine included in accomplishing the task! This makes it even easier to achieve the goal! Does anyone know what this is called?


Complex machines

A complex machine is when two or more simple machines are combined. For example, if we combined even more of the simple machines form the block example, we could help the block reach the next level even more easily:

Activity
Let’s test out one simple machine that makes the action of throwing something easier. We are going to make a catapult – after watching this video (1:55) can anyone name the simple machine that is used within a catapult?


Challenge: Try throwing a cotton ball into a cup and count how many times you get it into the cup out of ten attempts. Now try aiming the catapult into a cup and see how many of the ten attempts you get it into the cup.

Debrief:
Which of the two methods was more effective/easier for getting the cotton balls into the cup? Which simple machine was employed in the catapult?


Contact and non-contact forces

Gravity and air resistance can be taught together as air resistance affects the rate of falling bodies. Air resistance is a type of friction.

'Twirly whirlies' provide a suitable experiment as they are readily available and can be easily modified to promote experimentation. An A4 printable template is available here which will give you six per page. It is recommended that each student receives three each to encourage experimentation.

(CC BY 2.0, Source: https://au.pinterest.com/pin/503629170801754769/)

This template has three twirly whirlies. Children cut along the solid lines and fold along the dotted lines. Give each child three twirly whirlies and ask them to modify each and then make predictions about how they will fall. For example, attach a big paperclip to Part C for one and a smaller paper to Part C for another.

Friction

The following video (4:15) describes a world without friction.

Balanced and unbalanced forces

The following video (2:45) explains how forces are considered to be balanced if an objects remains at rest or at a constant velocity. This is in contrast to unbalanced forces which result in an object changing its velocity (i.e., speed or direction).

Moderated self-assessment


Relevant terminology (in alphabetical order): air resistance, axles, contact, force, friction, gravity, inclined planes, levers, non-contact, pulleys, screws, wedges, wheels.

Relationships between components:

  • Gravity is a force of attraction between objects. It is a non-contact force which is more noticeable between large objects such as planets and stars. 
  • Friction is a contact force which opposes movement between surfaces. 
  • Air resistance is a type of friction. Air resistance is still a contact force because air contains gases and particles.


Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

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