Lift a Load using Liquids
No one, not even a very strong human, is strong enough to lift a truck. However, our brains are smart enough to create a tool that can lift heavy objects for us: hydraulic lifts! You find them in body shops, on skyscraper construction sites, in wheelchair lifts, and in dentist chairs, and you will even build one in this activity! Try it out and discover how much more you can lift.
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
If you have ever used a wheelbarrow, you know it can help you lift heavy objects; lifting the handles of the wheelbarrow is easier than lifting the object itself. A hydraulic lift does the same; it allows you to move a heavy object with very little effort.
The term “hydraulics” refers to tools that operate by using moving liquids like water or oil. It uses a liquid and not, for example, air – which is a gas - because liquids are incompressible. This means that no matter how hard you press on a liquid, you cannot noticeably change its volume. Try it out! Fill a syringe with water, close its tip with a finger, and try to press the piston in. You will see that you cannot; even placing an elephant (if you were able to) on the piston would not compress the fluid in the syringe. But, what would happen when a tube filled with water connects the tip of this syringe to the tip of a second syringe? That is exactly what you will try in this activity!
In the effort to move something, it is not only important to push hard; the area over which the push is spread out can be important too. Think of a time when you played with playdough. Pushing a finger into the dough is easy, but pushing the palm of your hand into the dough is much harder. Because your hand has a larger surface area, your effort is spread out over a larger area and the playdough does not feel as much pressure. Is there a way to place your heavy object on a large surface so it creates less pressure? Do the activity to find out!
Observations and Results
You were probably able to lift much more weight with the large secondary syringe compared to the small secondary syringe, and the jar probably moved over a much shorter distance. That is exactly what happens in a hydraulic lift when the secondary piston is larger than the primary piston.
When you press one piston, the liquid inside the closed system feels the pressure, and it presses with an equal amount against the other piston. Because pressure is created by applying force over an area, a small push on a small area creates the same pressure as a much larger push on a much larger area. That is why a hydraulic lift can multiply a force: you push on a small piston, the pressure that is created moves through the liquid to a much larger piston, and the load on the larger piston feels a much larger push than the one you first made. For the same reason, you could move more weight with a large secondary syringe compared to a smaller one.
Did you see how liquid was transferred from one column to the other in the process? Because the volume of liquid does not change, the larger piston will not move as much as the smaller piston, but that is a small price to pay to be able to lift a heavy object.
On the left, a hydraulic lift where the secondary syringe is much wider than the primary syringe. A large toy truck is on the platform. The secondary piston does not stick out by much while the primary piston is fully pushed in. On the right, a similar hydraulic lift where the secondary syringe is much narrower. A toy car is on the platform. The secondary piston stick out completely lifting the car over a large distance.
More to Explore
Jack It Up! Lift a Load Using Hydraulics, by Science Buddies
The multiplication of force by a hydraulic system, by Wisc Online
Dam Design, Scientific American
Science Activities for All Ages!, from Science Buddies
Sabine De Brabandere, PhD, Science Buddies
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Simple machines, force, pressure
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