# 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.

# 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.

(Anyone reading this post who wants to ask a question or make a comment please feel free to do so)

# “Why can heavy things float”? ask Aiden (10)

Aiden, great question,a difficult answer. I hope that you have investigated which things float and which things sink. You should be able to look around you and say ‘That floats’ and ‘That sinks”. Think about this – when something sinks it seems to be breaking the surface of the water. What is it breaking? I pass this back to my team.

The attractive forces between water molecules are called intermolecular forces. Look at this post to find out more.  When the much bigger metal boat hits the water, because of it’s design (spread out) there are lots more water particles that push on the boat and keep it floating.  Squash the boat up into a small lump of metal  and drop it into the water. What do you think will happen? Let me know what you think by leaving a comment in the ‘Leave a Reply’ box below.

# “How do western toilets work?” was Vinay’s (10) question,

Vinay. These are the initial thoughts of my friends. I will reply later.

I’m back ….. So the siphon it is. For animations on siphons go to this great animation   where you will see a true siphon in action.

The amazing thing is that initially the siphon was thought to be delivered by air pressure. Then somebody created a siphon in a vacuum. So ideas have changed. Not everything in science is ‘absolute truth’ . One of the driving forces in science development is attempting to disprove accepted laws.

# Imran (age 10) asked “If I was to push a ball , how does it stay moving even after I pushed it?”

Imran. A great question. I would like to answer it in a slightly different way (you can sometimes do that with questions). After you push a ball it starts moving but does it stay moving?

When you push the ball you transferring your push (force)  to the ball and it moves. Newton (a great scientist and questioner) thought “Why does it stop moving? I have transferred my force to the ball and it should keep moving until it transfers that force to something else” But it does stops moving. I put this question to my friends and they came up with the following thoughts.

Why not investigate moving balls over different surfaces. You could use wood, paper, carpet, or the floor as surfaces and see how far the ball rolls BUT you have to make it a fair test. How do you create the same force?  How do you transfer the same force to the ball?

What would be your prediction (educated guess) about what the result would be? All scientist’s make predictions and then they test them.  My last question is, if there is something stopping the ball from rolling …. what do you think it is? has it got a name? If you have an answer you can leave it in the  ‘Leave a Reply’ box below. Want to ask another question …go to

# Maryam (age 10) asked a question on forces. “What do forces have to do with science?”

Maryam

What an excellent question. How do I answer this? Firstly I think we need to know what we mean by science. Here is what my friends said when I asked them the question.

My favourite definition of science is that it is ‘applied curiosity’. People who enjoy science have a curiosity about the physical and natural world that surrounds them. This leads them to investigate it.

Look at the see-saw in the picture above. Why does a small mass seem to balance a larger mass? Lets move the masses around and see if we can get other positions where they balance? This is curiosity in action.

So what about forces, are they part of the natural world or the physical world? What is a force?

The forces we meet every day are pushes and pulls. Pushes and pulls make things move.

Gravity is another force … jump off a chair and you are pulled to the ground, you moved because of the pull of gravity. Another force is friction – how does that affect movement? Force and movement are therefore intertwined. Investigate movement and you are investigating forces. And that leads to lots of questions. Do things always move at the same speed when a force is applied? Curiosity, curiosity, curiosity.

So please show your curiosity by asking more questions and I leave you with a question of your own. Are forces part of the natural world or the physical one, or both, or neither?

I hope this gives you some answers to your excellent question. Any more questions?