Personal Hovercraft

Introduction

Flying on air with the greatest of ease... is it a bird, a plane, no it’s a hovercraft! With a cushion of air on which to ride, the hovercraft is a student favorite.

Concepts

• Air pressure
• Friction
• Newton Law's

Experiment Overview

Demonstrate the concept of a hovercraft and Newton’s Laws.

Materials

Safety Precautions

This demonstration may present dangerous conditions to both the demonstrator and the observers. Only perform the demonstration in a large area free of obstacles with a flat, smooth floor. Operate the leaf blower as suggested by manufacturer instructions. Carpeted or grassy areas are not recommended. The leaf blower must be turned off before adding or removing any weight.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Unplug leaf blower and store all components for future use.

Prelab Preparation

Remove any extension components of the leaf blower—use manufacturer’s instructions.

Procedure

1. Decide where the demonstration will occur. A large area with a smooth flat floor that is free of obstacles is needed.
2. Place hovercraft flat on floor skirt side down.
3. Place the leaf blower output through the hole cut in the hovercraft (see Figure 1). Note: If using a leaf blower other then the recommended one, make sure leaf blower nozzle fits snugly into the flexible coupling.
4. Attach the battery or extension cord to the leaf blower and plug into a safe electrical outlet.
5. If desired, add weight.
6. Turn on the leaf blower.
7. Demonstrate to the students the ease at which the hovercraft moves a load across the floor.
8. Turn off the leaf blower before moving or shifting any weight—each and every time.

Teacher Tips

• Practice this demonstration before performing it in front of an audience. It is helpful to become familiar with the hovercraft and how it responds before demonstrating in front of the students.

• The apparatus may be reused many times.
• Have a person assigned to keep the extension cord free from obstacles, getting tangled, and the hovercraft itself.
• The hovercraft may be easily tipped if the weight on the hovercraft is not balanced at all times. The lower the center of gravity of the weight on the hovercraft, the more stable the hovercraft will be.
• The hovercraft must be turned off before moving or shifting any weight. This prevents the hovercraft from moving unexpectedly.
• With one hovercraft Newton’s First, Second, and Third Laws may be demonstrated.
  Newton’s First Law of Motion
  1. Set up a measured area of distance that the hovercraft can freely travel.
  2. Turn the hovercraft on and apply a measured force of pull (fraction of a second) to the hovercraft with a spring scale or other measurement device.
  3. As the hovercraft moves across the floor, time the distance traveled.
  4. The hovercraft should have relatively constant speed (shown by the time needed to cover a measured distance takes about the same amount of time).
  5. Example: Apply 10 Newtons of force and measure the distance traveled over 10–15 meters, measuring every half meter.

  Newton’s Second Law of Motion

  6. This set-up is similar to the first law demonstration however this time the student will pull the hovercraft using a constant measured force.
  7. Have students pull with a constant force over a measured area using constant forces less than the original 10 Newtons (i.e., 1, 2, 3).
  8. Measure the distance traveled per time.
  9. The hovercraft should show that the hovercraft actually accelerates (shown by the time needed to cover a measured distance takes less and less time). 

  Newton’s Third Law of Motion

  10. For a visual demonstration, have a student balanced on the hovercraft safely throw a basketball.
  11. Prepare the student for the hovercrafts movement so that they do not lose their balance.
  12. With two or more hovercrafts Newton’s First, Second and Third Laws may be demonstrated. 

  Collisions

  1. Gently push two hovercrafts without added weights toward each other.
  2. Record observations of the collision in terms of the type of collision and any acceleration that occurred.

  Newton’s First Law of Motion

  3. Gently push the hovercraft and notice if the direction and speed (velocity) appears to remain constant or changes before the hovercraft slows.
  4. Record observations in terms of Newton’s First Law of Motion.
  5. Gently push one hovercraft toward a levitating stationary hovercraft.
  6. Describe the observations in terms of Newton’s First Law of Motion.

  Newton’s Second Law of Motion

  7. Gently push one hovercraft toward a levitating stationary hovercraft.
  8. Record observations of the collision on the worksheet. Describe the observations in terms of Newton’s Second Law of Motion.
  9. Add mass to a levitating stationary hovercraft and gently push another hovercraft toward the more massive hovercraft. Note: Repeat with three different amounts of mass.
  10. Describe the observations in terms of Newton’s Second Law of Motion.

  Newton’s Third Law of Motion

  11. Repeat step 7. Try to push both hovercrafts with the same amount of force.
  12. Describe the observations in terms of Newton’s Third Law of Motion.
  13. Another option is to have students on the hovercrafts play catch with each other using a basketball.

Discussion

Hovercrafts are used all over the world. One of the several advantages to hovercrafts is their ease of use in otherwise difficult terrain. Areas that are typically hard to reach by boat or land vehicles may be easily accessible by hovercrafts (e.g., muddy and swampy areas, thin ice, rocks, rapids, sandbanks). The military uses hovercrafts for ship to shore runs. The hovercraft can travel from the ship over the water, the beach, and further inland delivering troops and gear quickly and dry. A hovercraft may be safer than a boat because a boat has to stop on the beach whereas a hovercraft can travel on water and inland—offering protection from the open area of the beach.

How does a hovercraft work?

Air pressure is the main principal behind the hovercraft. A simple hovercraft consists of three parts- platform, fan, and skirt. The platform is the main structure of the hovercraft. A motorized fan is used to move enough air to change the air pressure—in this case a leaf blower. A skirt is used to trap the air between the platform and the ground creating a plenum chamber. The plenum chamber is an area of positive pressure—the pressure is greater than its surroundings.

A hovercraft acts very similar to a puck on an air hockey table. The fan produces force to reduce friction between the hovercraft and the ground. Because of the reduced friction, the hovercraft tends to go in whatever direction toward which it is pushed. With the reduced friction Newton’s First Law can be demonstrated. With two hovercraft collisions and Newton’s second and third laws can be simulated.

Newton’s First Law of Motion is called the law of inertia. If an object is in motion with a constant velocity, the object tends to stay in motion maintaining that velocity unless acted upon by an external force. If an object is at rest, the object tends to stay at rest unless acted upon by and external force. Inertia may be defined as the tendency of an object to resist change in motion.

Newton’s Second Law of Motion states that force (F) applied by an object is equal to the mass (m) of the object multiplied by the object’s acceleration (a) (see Equation 1). In relation to acceleration, the mass of an object is inversely proportional and the force needed to accelerate the object is directly proportional. In other words, if the same force were applied to two objects of different masses, the object with less mass would experience a greater acceleration than the more massive object.

Newton’s Third Law of Motion indicates that for every force there is an equal and opposite reaction force. When one object pushes against another, the force of the first object is equal in magnitude and opposite in direction to the magnitude and direction of the force applied by the second object.

References

Thanks to Jim Szeszol, retired from Naperville Central High School, Naperville, IL, for bringing this idea to Flinn Scientific