Science Master Special A Push-Pull Meter

Many years ago I and my class made a Push-Pull Meters with dowel rod and a cotton reels and had great fun with them, measuring all sorts of pushes and pulls.OK we could have used conventional force meters, the school had enough of them for class use, however making one yourself and then using it seems to make a big difference in understanding.

A recent question made me look for my plans – no chance. Search the internet – no luck. My team were of no help so I therefore decided to do the obvious thing, make one myself.

These are the drawings of my endeavours. The equipment list is cotton reel (wooden would be nice but if it’s plastic ok), a length of dowel rod with a diameter which will allow it to pass through the central hole of the cotton reel, an elastic band (probably 4 cm long but have a set of them for experimentation), a paperclip which is opened up to make a hook, some drawing pins or sellotape …….and I think thats it.

Once constructed the next task it to calibrate it. If you have access to a set of weights, great. you can create a little bag which will hold them, hang it on the hook and away you go. A 1kg mass will apply a 1 Newton force on the elastic band. This is where the choice of the elastic band is important – a thin band is obviously much more sensitive than a thick band. On the other hand, why not make up your own scale of push a pulls – a five marble/ 3 marble/1 marble push or pull. Below are the images that I created for my answer to the 10 yr olds question.


“When the Sun blows up will Mercury smash into Earth?” asks Flynn and Freddie (10)


Below is a short video of the expansion of the Sun. Again this is a hypothesis based upon observations of our Universe.

The expansion is thought to be caused by firstly the Sun running out of fuel (it uses  Hydrogen, converting it by a fusion reaction to Helium). As the Sun cools the centre will expand, (any thoughts on what might cause this?) pushing out the rim of the Sun and consuming Mercury, Venus and The Earth and eventually it becomes a Red Dwarf. It is suggested that Mars will survive.

What is the difference between a hypothesis and a theory?

Hope this helped. Please comment or ask another question.

Angus and Lachie(10) ask “Are aliens real?”

……………..I personally think that with so many potential places where life, in what ever form could have developed that aliens do exist and we have now, to wait, for contact.

Of interest is that life started developing on Earth in a very different way from how we would expect. The early bacteria were, it is thought, cyanobacteria. This bacteria ‘eats’ Nitrogen gas and exhales Oxygen and in doing so killed itself by poisoning its atmosphere. The Earths atmosphere moved from being a Nitrogen to an Oxygen atmosphere. So ………………………..this might not always happen on other Earth’s thus the type of life which humanity may meet in the future could be Nitrogen based.

The cyanobacteria do still exist in Earth’s deep oceans.

Also look at a previous post on aliens.

“If all living things were in one food chain, what would be at the top?” asks Chelsea and Ashli (10)

Thanks team. I found a nice little revision site on food chains that you might like to try, find it at Food Chain Game.

Now to your question. Firstly it might be a little difficult putting all living things into one food chain. Secondly do you think it would be humans?  Ecologists (They are scientists who specialise in studying the living environment) rank species by their diets using a metric*  called the trophic level scale. Plants, which produce their own food, are given a rank of 1. Herbivores, which eat only plants, are ranked 2. The fiercest of meat-loving predators, such as killer whales, are rated at 5.5. Humans are rated at 2.5 which is the same level as a pig.

If you want to make a comment please use the box below or you could ask another question.

* metric as a noun means a standard scale of measurement so you could call a temperature scale a metric or any other standard scale of measurement a metric.

(updated 13/9/17 -changed metric to measurement)
(updated 15/9/17 – ‘measurement’ back to ‘metric’ after realising it was the correct word in the context in which it was presented, added addendum explaining it’s use as a noun)

Billie and Zali (10) asked “How does the activator form slime?”

Sorry team.  You have provided some good background material. The important thing about making SLIME is that all the ingredients in it’s making (The Activator, the PVA and water)  have something in common, lots of O-H chemical bonds. It is these that make the SLIME a reality. Look at the diagram of a PVA molecule and count the number of O-H bonds. Remember this is a Polymer so the image below is just one bit of a much bigger molecule of PVA.

So what is it about the O-H bonds that make them so important.

Look at the following short video ….



It’s all due to Hydrogen bonding. Everything is attracted to everything else by the Hydrogen bond environment that is introduced when you put all of the ingredients together. SLIME becomes the reality.

Think about it. Make a comment or if you don’t understand a complicated bit then please- Ask another Question

(revised 13/9/17 – PVA is polyvinyl acetate not polyvinyl alcohol, Diagram of PVA included and last paragraph revised)

“Why do volcanoes erupt?” asks Silas and Zakk (10)


Thank you Silas and Zakk for your question. My team are correct it’s all about pressure. All volcanoes have a thin ‘lid’ of solid rock which which is solidified magma. Underneath the lid is lots of molten magma which is heated by the Earth’s central core.

Things can happen to this magma. Some of it could cool, and solidify. You could also get convection currents like you do in any hot liquid. These can increase the pressure (push) on the volcano lid, break it and the pressure is released like the liquid in a bottle of fizzy drink.

Want to make a comment, please make it in the box below. Not sure about something …ask another question.

(revised 13/9/17  Magna misspelling and added support text)

Alice, Daisy, Eliza (10) asked “What chemical makes objects glow in the dark?”

Thanks team. I think we will start by looking at the meaning of the words that end in the term ‘escence’.

Fluorescence is the the almost instantaneous emission of light by a chemical that has absorbed light or some other form of energy and  then re-emits it.
Chemiluminescence is used to describe the production of light from a chemical reaction.
Bioluminescence is used to describe the production of light from a living organism. It is a form of chemiluminescence as it is chemicals within the organism’s body that produce the light.
Incandescence is the emission of light from a hot body. A heated piece of iron will glow.
Phosphorescence is the slow emission of light from a compound that has absorbed some energy, in some form…might be radioactive energy.

Note all of them involve , at one time gaining energy and then re-emitting it or chemicals moving from one state to another where the final state is of lower energy.(If you want to find out a little bit more on energy go to this Science Master Special)

If you have access to a low intensity UV torch ( check with an adult) you can look at at the compound Quinine for an example of fluorescence. Quinine is a compound in Tonic Water. In a dark room shine the torch (a UV torch produces BLACK light) on the bottle of tonic water and watch what happens. You can then make some ice lollies using the tonic water and again see if they are fluorescent.

Thanks for the question. If you want to make a comment feel free to do so in the box below…or maybe…you have a further question?

(Revised 13/9/17 – added energy link)

“What was the first plant that ever grew on Earth?” asks Mahdiyat (8)

So what now? Thanks team, some good answers.

It would be great if we could do some small investigations using Moss.

1.Firstly let us confirm that the moss has no stems or flowers.

2. Secondly a more long term experiment. Try ‘planting’ your moss on a rock. Before planting look closely at the surface of the rock. compare the surface 6 months after planting (and not disturbing the Moss).

Now a story ……..

The moss was the Earth’s first plant and it took over the world. It damaged the rocks it settled on and it took all of the Carbon Dioxide out of the atmosphere. This made the Earth very very cold (the first ice age). The coldness killed most of the moss and as the Carbon Dioxide built up again it allowed other plants to share the Earth with it.


How does the wind manage to topple things like wheely bins over? With the bins being big objects how is this possible? asks Imran (10)


A useful place to start Imran would be to look at the way in which wind is can exert a very strong force. Wind is created by the Sun warming up the ground around us and the air. Sorry team, I don’t think the wind does much pulling.

Air is made up of tiny molecules. When molecules are heated, they move faster. As they move faster they become become spaced farther apart, which makes the air less dense (meaning that there are fewer molecules in a given volume). This also means that the air has a lower overall pressure (pressure is the push of the gas on it’s surroundings. In comparison, cold air is made of more tightly packed molecules, and so it is denser and has relatively higher pressure.

The warmer, lower pressure air begins to move upwards and therefore it creates space below it which is filled by the colder higher pressure air. A wind is created. The hotter the air near the surface of the Earth the lower the pressure and the faster the rise. The 2017 hurricanes were caused by the hot sea and hot temperatures near the surface.

Can you measure how much push (force) is needed to push over a wheely bin?  Let’s first make our own push-pull measurer. You will need an elastic band, cotton reel, a couple of drawing pins, some sellotape and a paper clip to make your own measurer.

You can use it directly to measure pushes and pulls just by seeing how far the cotton reel moves up the dowel rod. It would however be better if we calibrated the rod in some way. In the images below the rod has been calibrated in Newtons (theses are the units of force). To do this a 500 gramme mass was attached to the hook. It is known that a 500g mass will exert a force (pull) of 1/2 Newton. So when the mass is attached, the elastic band will stretch, and the dowel rod will be pulled down. The distance on the rod between the ‘no’ force point and the 500g point is therefore equivalent to half a Newton.

It is estimated that an 80 mph wind would have a push of about 400 Newtons per square metre and be able to move a car. A breeze 5 mph might have a push of between 5-10N per square metre. You could try your meter on a sheet of cardboard in a strong breeze and see what you get.

Imran your question was very interesting to answer and you might have some difficulty in understanding some of the stuff above. If that is the case and also for anybody else reading this PLEASE ask another question or make a Comment.

Mariah (7) asks “Why are pushes and pulls forces?”

Thanks team and thanks Mariah for the question.  My team are quite correct there are lots of pushes and pulls. Can you think of more? What about gravity? That pulls things to the ground. What about the wind, that pushes things.

In science and in our daily life we put things into groups. The things in the group all have something in common. All fish are grouped together, they can all breathe underwater. Can you see anything else they have in all fish have which is the same?
All bicycles are grouped together, they all have two wheels. They also have some other things in common (the same).

If all forces are grouped together , they all involve pushes and pulls. The group that pushes and pulls is called forces.