Teacher Notes

Principles of Hydraulics

Student Laboratory Kit

Materials Included In Kit

Force Apparatus
In-line on/off valve
Load stand
Luer® female, with hose barbs, 2
Luer lock T-connector
Luer male, with hose barbs, 3
One-way valves, 2
Plastic tubing, 5 ft
T-connector with hose barbs

Additional Materials Required

Water, 400–800 mL
Beaker, 500–1000 mL
Mass, 1000-g
Ruler
Spring scale, 1000-g capacity
Support stand
Support stand clamp

Prelab Preparation

Plastic tubing may be cut to appropriate lengths prior to laboratory work. This will save time and tubing.

Safety Precautions

This activity is considered nonhazardous. Please follow all laboratory safety guidelines.

Disposal

Water is the only item requiring disposal from this activity. All materials may be dried and stored for future use.

Teacher Tips

  • Enough materials are provided in this kit for one laboratory group of students. The lab can reasonably be completed in one 50-minute class period.
  • In this activity, force is measured in grams instead of Newtons to make the comparisons easier to see and calculate. Newtons can be used if spring Newton scales are available where g = 9.81 m/s2.

Correlation to Next Generation Science Standards (NGSS)†

Science & Engineering Practices

Developing and using models
Planning and carrying out investigations
Analyzing and interpreting data
Using mathematics and computational thinking

Disciplinary Core Ideas

MS-PS2.A: Forces and Motion
HS-PS2.A: Forces and Motion

Crosscutting Concepts

Systems and system models
Scale, proportion, and quantity

Performance Expectations

MS-PS2-2: Plan an investigation to provide evidence that the change in an object’s motion depends on the sum of the forces on the object and the mass of the object
HS-PS2-1: Analyze data to support the claim that Newton’s second law of motion describes the mathematical relationship among the net force on a macroscopic object, its mass, and its acceleration.
HS-PS2-4: Use mathematical representations of Newton’s Law of Gravitation and Coulomb’s Law to describe and predict the gravitational and electrostatic forces between objects.

Sample Data

Sample Data Part I. Volumes/Distances

Diameter of force apparatus plunger ___15___ mm
Diameter of load stand plunger ___22___ mm
Volume forced out of small syringe ___10___ cc
Volume forced into the large syringe ___10___ cc
Distance traveled by small syringe ___60___ mm
Distance traveled by large syringe ___28___ mm

Calculation

  1. (Area of circle = πr2)

    Area of small plunger = ___177___ mm2
    Area of large plunger = ___380___ mm2
    Ratio of small plunger area : large plunger area = ___0.47___
    Ratio of distance traveled by large syringe : small syringe = ___0.47___

  2. (Volume of cylinder = πr2h)

    Volume displaced by small plunger = ___10620___ mm3
    Volume displaced by large plunger = ___10640___ mm3

Part II. Lifting Power

Spring scale force to operate system (overcoming friction) ___220___ g
Spring scale force to lift 1000 g ___650___ g
Actual force needed to lift 1000 g ___430___ g

    1. What is the ratio of the lifting force to the mass lifted? ___0.43___
    2. How does this ratio compare to the ratio of the plunger areas?

      Nearly equal.

    3. In an ideal system how should the ratios compare? Explain any possible sources of error.

      Ideally, the ratios would be equal. Spring balance measurements, diameter measurement and human error are possible sources of error.

    4. What does the ratio mean in terms of the amount of force needed to lift a load?

      The smaller ratio means it takes less force to lift a heavy object, but the object also travels a shorter distance compared to the force.

  2. You have operated an exact model of a hydraulic jack or car lift. How could this model be used to show how car brakes work? Which part of the model would represent the brake pedal? The brakes at the wheel? What does the beaker of water represent?

    The small plunger could represent the brake pedal, the large plunger the brake cylinder at the wheels, and the beaker of water the brake fluid reservoir.

Recommended Products

Item No. Description

Student Pages

Principles of Hydraulics

Student Laboratory Kit

Introduction

Step on the brake pedal and the car comes to a stop. How does the pedal apply pressure to the wheels to stop the car? The same principles apply when a car is raised off the ground with a hydraulic lift. Build a hydraulic lift system and discover hydraulic principles.

Concepts

  • Pascal’s law
  • Hydraulic pressure
  • Force multiplication

Background

The basic idea of every hydraulic system is based on a simple principle. Force applied at one point is transmitted to another point through an incompressible liquid. A simple hydraulic system can be pictured as follows (see Figure 1).

{13925_Background_Figure_1_Simple hydraulic system}
Blaise Pascal (1623–1662) formulated the basic laws of hydraulics in the mid 17th century. He discovered that pressure exerted on a fluid acts equally in all directions. Pascal’s law states that pressure on a confined liquid is transmitted undiminished in all directions and acts with equal force on equal areas and at right angles to the container’s walls. This allows a hydraulic system to have a connecting “pipe” of any length and shape and have the force applied at some distance away (e.g., the brake pedal and the wheels).

Another key feature of hydraulic systems is force multiplication. Since the pressure is equal everywhere, the force applied on a small piston will be translated to pressure on the large piston. The ratio of force per area will be equal.
{13925_Background_Equation_1}
Trading force for distance is very common in mechanical systems. It is also true in hydraulic systems. In a hydraulic system if the size of one piston relative to another is changed, the force applied to the small piston can be multiplied in the work completed at the large piston. This multiplication can be utilized to lift objects or apply great force over a shorter distance (see Figure 2).
{13925_Background_Figure_2_Force multiplication}

Materials

Water, 400–800 mL
Beaker, 500–1000 mL
Force apparatus
In-line on/off valve
Load stand
Luer® female, with hose barbs, 2
Luer lock T-connector
Luer male, with hose barbs, 3
Mass, 1000-g
One-way valves, 2
Plastic tubing, 5 ft
Ruler
Spring scale
Support stand
Support stand clamp
T-connector with hose barbs

Safety Precautions

This activity is considered nonhazardous. Please follow all laboratory safety guidelines.

Procedure

Part I. Volumes/Distances

  1. Gather all materials and set up the model hydraulic system as shown in Figure 3. To position the metal wire loop of the force apparatus around the plastic tubing so that it can be pulled down without interference from the tubing, remove the wire loop from the brackets on the syringe plunger. Then reconnect the wire loop so that the wire loop hanger is perpendicular to the hydraulic line. The U-shape hangs below the tubing and doesn’t touch it.
    {13925_Procedure_Figure_3_Model hydraulic system}
  2. Remove the top wooden block from the top of the load stand.
  3. Remove the plungers from the force apparatus and the load stand. Use a ruler to measure the diameter of each plunger to the nearest mm.
  4. Record the diameter measurements in Part I of the Hydraulics Worksheet.
  5. Replace the two syringe plungers and push the load stand plunger completely down to the bottom of the syringe tube.
  6. Place the two free ends of the plastic tubing into the beaker of water. Be sure the tips of the tubing are completely under water
  7. Turn the on/off valve to the open position—valve handle parallel to the tubing line.
  8. Lift the plunger in the force apparatus. Lower the plunger into the syringe tube. What happens to the air in the system? Where does the air go? Keep pumping the plunger up and down until no more air escapes and there is no air in the system.
  9. Close the on/off valve—valve handle perpendicular to the tubing line.
  10. Raise the plunger in the force apparatus. Lower the plunger and notice what happens to the plunger in the load apparatus.
  11. Slide the plunger in the force apparatus up and down several times and observe the results.
  12. Open the on/off valve and slowly lower the syringe plunger in the load apparatus.
  13. Raise the plunger in the force apparatus up to the 10-cc mark. Note its exact location on its bottom-most edge. Also note the exact location of the bottom edge of the larger syringe in the load apparatus.
  14. Close the on/off valve.
  15. Depress the small plunger to the bottom of the syringe cylinder in the force apparatus. How many cc of water were expelled? Record this amount in Part I of the Hydraulics Worksheet.
  16. How many cc of water were pushed into the larger syringe in the load apparatus? Record this amount in Part I of the Hydraulics Worksheet.
  17. Use a ruler to measure the distance traveled by each plunger. Measure to the nearest mm and record this amount in the Hydraulics Worksheet.
  18. Complete the calculations for Part I of the Hydraulics Worksheet.
Part II. Lifting Power
  1. Lower the plunger in the load apparatus syringe and place the wooden block platform on the top of the syringe and into the hole in the block. Make sure it is on securely and is level.
  2. Raise the plunger in the force apparatus and hook a spring scale to the wire loop hanging below the syringe. Do this at the edge of the table so that the spring scale can hang below the tabletop.
  3. Pull down on the spring scale with a slow and even pressure until the plunger moves extremely slowly and steadily downward. Have a partner read the spring scale. Repeat the procedure several times until an accurate reading is determined.
  4. Record the spring scale reading in the Hydraulics Worksheet for Part II. This reading represents the force necessary to operate the system and overcome the friction created in the entire system.
  5. Lower the plunger in the load apparatus and carefully balance a 1000-g weight on top of the large plunger.
  6. Attach the spring scale to the force apparatus and determine the force necessary to lift the 1000-g mass at the same slow, steady rate measured for the empty system. Repeat the lifting procedure several times as a partner takes readings on the spring scale. Measure when the plunger is moving slowly and evenly.
  7. Record the reading on the Hydraulics Worksheet.
  8. Calculate the actual force needed to lift the 1000-g mass, without friction.
  9. Answer the questions for Part II of the Worksheet.
  10. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

13925_Student1.pdf

†Next Generation Science Standards and NGSS are registered trademarks of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.