When people mention the word “hydraulics”, they could be talking about pumps, turbines, hydropower, erosion, or river channel flow.  The term “hydraulics” means using fluid power, and deals with machinesand devices that use liquids to move, lift, drive, and shove things around.

Liquids behave in certain ways: they are incompressible, meaning that you can’t pack the liquid into a tighter space than it already is occupying.

If you've ever filled a tube partway with water and moved it around, you've probably noticed that the water level will remain the same on either side of the tube.

However, if you add pressure to one end of the tube (by blowing into the tube), the water level will rise on the opposite side. If you decrease the pressure (by blowing across the top of one side), the water level will drop on the other side.

In physics, this is defined through Pascal's law, which tells us how the pressure applied to one surface can be transmitted to the other surface. As liquids can't be squished, whatever happens on one surface affects what occurs on the other.  Examples of this effect include siphons, water towers, and dams. Scuba divers know that as they dive 30 feet underwater, the pressure doubles. This effect is also show in hydraulics - and more importantly, in the project we're about to do!

But first, let's understand what's happening with liquids and pressure:

Here’s an example: If you fill a glass full to the brim with water, you reach a point where for every drop you add on top, one drop will fall out.  You simply can’t squish any more water molecules into the glass without losing at least the same amount. Excavators, jacks, and the brake lines in your car use hydraulics to lift huge amounts of weight, and the liquid used to transfer the force is usually oil at 10,000 psi.

Air, however, is compressible.  When car tires are inflated, the hose shoves more and more air inside the tire, increasing the pressure (amount of air molecules in the tire).  The more air you stuff into the tire, the higher the pressure rises.  When machines use air to lift, move, spin, or drill, it’s called “pneumatics”. Air tools use compressed air or pure gases for pneumatic power, usually pressurized to 80-100 psi.

Different systems require either hydraulics or pneumatics.  The advantage to using hydraulics lies in the fact that liquids are not compressible. Hydraulic systems minimize the “springy-ness” in a system because the liquid doesn’t absorb the energy being transferred, and the working fluids can handle much heavier loads than compressible gases.  However, oil is flammable, very messy, and requires electricity to power the machines, making pneumatics the best choice for smaller applications, including air tools (to absorb excessive forces without injuring the user).

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52 Responses to “Hydraulic Pneumatic Earth Mover”

  1. katrina_webster says:

    You don’t need to press the glue. When you pull the trigger it should dispense some.

  2. fruityveggiegirl says:

    This is so cool. Hope to make it soon.You could even add a motor to make the wheels move on it’s own as well as arm control. I want to make it to enter into the LA County Fair (at least one of these vehicles)

  3. Hmmm… it sounds like the tubing is a little big for the syringe tip. What happens if you put a couple layers of masking or duct tape on the nose of the syringe and then try again? You can also run a bead of hot clue between the tubing and the syringe (it won’t take much) to seal it up the way you would put silicone around a bathtub.

  4. Do you have any tips for sealing the syringe and tubing? Ours just kept leaking. We tried lots of hot glue, duct tape, electrical tape — still leaking.

  5. Tammie Earnest says:

    on the video you talked about a “KIT” what is that?

  6. Lori Salvino says:

    Is it possible to use regular size popsicle sticks instead of the tongue depressor size popsicle sticks?

  7. The rubber seal must not be working well – I’d get another set from the store. It’s really hard to fix these, since the fit is so tight between the cylinder and the plunger.

  8. You can use steel wire, or anything else to hold the syringes in place. I’ll fix the shop list soon!

  9. Michelle Stevens says:

    I noticed in the video that you used copper wire, but it wasn’t on the list of supplies. Is there a substitute that I could use?

  10. Michelle Stevens says:

    2 of my hydraulic pumps sprung leaks and stopped working 🙁
    I repeatedly tried to seal them with hot glue, and it worked for a while, but then they started leaking again!!!
    Do you have any ideas on what went wrong?

  11. Loreena Baker says:

    Ok thanks.

  12. Any lightweight plastic cup. If your is too tall, cut it down to size (like cut it in half and discard the top).

  13. Loreena Baker says:

    What kind of cup do we have to use???????????

  14. You’re welcome! So glad you’re enjoying the content!

  15. Lola Hunjul says:

    Thank you so much for the great idea. I enjoyed the experiment. Many thanks

  16. Beth Symes says:

    it look cool zachy

  17. Sandra Sires Kraha says:

    Aurora I did this project but I did it with a erector set. I will send a photo soon. P.S . We didn’t have a drill bit small enough so my dad showed me a trick that he learned from his grandpa. The trick is that if you need to drill through wood or plastic but don’t have the right drill bit you can use a nail the same size as the hole you need.

  18. Emily Crawford says:

    This project is so cool and working so well for me. I have a question: Would it be correct to say that each syringe system works like a sort of indirect lever?

    -Mary Crawford (age 12)

  19. No, not a silly question!
    Yes, because it uses different levers to make the bucket move. Cranes are based on levers. I just added the hydraulic part also (and we don’t have a unit on fluids, or you’d also find it there.)

  20. Suzannah Kolbeck says:

    This may be a silly question, but why is this in the unit on levers? Because of the way it is constructed?

  21. Darlene Young says:

    This was awesome! It works perfectly for us. My 12 year old is loving this program. It is so much better than the book work we struggled with last year. He is actually choosing to do science whenever he has a chance now that he has discovered what the program has to offer. We found all the parts at home, our local pharmacy and pet store(tubing). Thank you so much for this great program.

  22. Carmenza Coleman Salgado says:

    What a great idea, Aurora

  23. Julie Kuehler says:

    here is an idea use 2 sports water bottle caps with balloons on both sides to propel the earth mover forward

  24. It’s easier than you think… simply remove the INSIDE piston from both ends, fill it with water to the top of both, have someone press in one piston (water should shoot out other other side, so do this over the sink), and when it’s fully depressed, insert the other piston. Try to get rid of all the bubbles by filling the tubing all the way to the top of the syringe housing. You can even put in colored water!

  25. Lorelei Grecian says:

    HELP. How do you refill the syringes? I made the crane part cardboard and can’t dip the whole thing in water! :0

  26. Lorelei Grecian says:

    fixed the car its sooooooo awesome!!!!!!!!!!!!!
    This program is sooo great!!!!!!!!!!!!!!!!!!!!!!

    Earth Mover Project

  27. Lorelei Grecian says:

    Thanks but I thought of putting bigger wheels on the back. But I will send you a pic 🙂

  28. Lorelei Grecian says:

    The bottom of the big sryinge in the back where it is hooked on to the tube on the bottom is making my car go of the ground. HELP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!11

  29. Lorelei Grecian says:


  30. Thanks for the tip! If you send it to science@superchargedscience, I can post it for you.

  31. Lorelei Grecian says:

    For the two popsicle sticks you had to cut in half, my Mom drilled them but they split. So we are using cedar pieces of wood. How do you send a pic?

  32. The drill is the only way to keep the sticks from splitting because you need to remove the material slowly, whereas using a tack and razor shove the wood and compresses it inside the hole (and the stick can’t take this kind of pressure so it splits). What if you use a sturdy piece of cardboard or blocks of foam? Can you find a way to make those work in place of the popsicle sticks?

  33. Lorelei Grecian says:

    Is there any other way you can make a hole in the popsicle stick besides drilling a hole, hole punching, or using a rasor blade? Moms busy so I can’t use the drill, tried bolth other ways didn’t work, the popsicle sticks kept splitting in half. 🙁

  34. Lorelei Grecian says:

    Thanks a bunch!!!!!!!!!!!!!!!!!!!!!!!!! 🙂

  35. Sure – any size popsicle sticks (or even stiff foam pieces) can work. You can use film canister lids, milk jog tops, etc for your wheels… or rip them off an old toy.

  36. Try your local pet or veterinarian place? Hobby shops also have these, or look online at a medical supply company like Vitality Medical.

  37. Lorelei Grecian says:

    Oh and can you use normal posicle sticks instead of toung deppresser size? Where can you get the wheels?

  38. Lorelei Grecian says:

    I want to do this so much but where do you get the tubing and syringes? It looks awesome!!!!!!!!!! 🙂

  39. We got ours from a local medical supply place, but I have also found them at farm supply stores. I know some people have asked their vets for needle-free samples for kid projects. Let me know if you still have trouble!

  40. Kim Spadgenske says:

    Where do you get the syringes?

  41. Kim Brown says:

    We’ll give it a try.

  42. Those will work just fine. So glad you are enjoying the program! I really like the experiment you’re doing now – I haven’t seen any other decent hydraulics experiments for kids that turn into something cool like this one does. 🙂

  43. Kim Brown says:

    We’ve found all supplies necessary except the brass fasteners. For some reason, no store in our town sells
    them. I can order on line but have only found them 1″ long. Won’t this be too large?
    Thanks for your help. We LOVE Supercharged Science! Thanks for all your work.

  44. I am preparing the lesson for Unit 4 and see on the shopping list where it states I can purcharse the pneumatic earth mover kit from you. I have gone to the website however and cannot find where I may do that. May you please help me with this? Thank you.

  45. Just make sure not to get any glue IN the tubing, and you should be fine. 🙂

  46. Elaine Deppe says:

    Can I hotglue the tubing and syringes together to make the connection stronger

  47. Anonymous says:

    Oh goodness, I don’t know why I didn’t think to submerge the whole thing. Thanks. Would a place like Home Depot have the tubing? When I call places to ask they never know what I’m talking about. What section in the store do I find it?

  48. I am so glad you’re enjoying the project and sharing it with others! 🙂

    To fill up the syringes, first remove the plungers, then connect a syringe to each end. Place underwater (like a sink full of water) to fill both to capacity. Insert one of the plungers and press it all the down. Insert the second plunger. Lift from water. You should have a solidly connected set of syringes without air bubbles. If you do have a big bubble or two, remove one of the plungers and fill the syringe with water until it spills out the top before reinserting the syringe.

    When we teach this to kids, I usually get a big roll of tubing from the hardware store, but I always take the syringes with me so be sure I have the right size. I know that vet clinics sometimes donate a set of syringes for kid’s projects, but sometimes they hare the needle-type (and those aren’t the ones you want!). You can also try a pharmacy, but they tend to be more expensive than the farm supply stores. Have you tried Amazon.com?

    As a side note, when I teach this project to kids, I sometimes replace the popsicle sticks with foam blocks to make construction a bit easier. Although we don’t have this variation on video, perhaps your kids can figure something out? I also color-code the syringes by using food dye, so kids can easily see which syringe controls which on the mover.

    Have fun!

  49. Anonymous says:

    My kids made this to show at our home school display day and it was the biggest hit! There wasn’t a kid in there who didn’t give it a try. When people ask “how did you learn to make that?”, we always toot the Supercharged Science horn and tell people we love it!!! Now I’ve had other parents want me to teach their child how to make this. I’ve got 6 kids coming over to do this with my 3 kids. Can you tell me a good place to buy the extra tubing and syringes? Our local farm supply store had syringes but not the tubing and they seemed over priced. Is there someplace online to order this stuff cheaper?

    Also, we had a lot of trouble re-filling the water in the tubes once it is built. How do you suggest doing this?