Seibun Mind-Development® Activities

 Hovercraft LAB 3 – Newton’s Second Law of Motion

Centripetal Forces and Acceleration

• Purpose:

  • To observe Newton’s Second Law of Motion using a Seibun Hovercraft Kit

Information

Sir Isaac Newton developed three laws of motion. The Newton’s Second Law of Motion states an object will change its state of motion when acted on by an unbalanced, outside force.

Changing motion is also called acceleration. The motion of an object can be changed in one of two ways. The object can change speed by moving faster or by slowing. An example of this type of acceleration is seen as a car moves faster when the gas pedal is pushed. It is also seen when a car slows as the brake pedal is used. Both using a gas or brake pedal causes a force. An unbalance or unopposed force on an object causes an acceleration.

Changing motion includes changing direction. A force must be applied to change the direction of an object. The force causes an acceleration. This type of acceleration and force have a special name. The special term is CENTRIPETAL. The acceleration and force are inward or toward the center.

• Equipment –

  • Seibun Hovercraft, smooth surface

  • Rectangular cookie sheet and water works well

  • tape, thread or light string

Procedure

1.      Find a smooth and level surface. Filling a large, rectangular cookie pan with water works well for a very level and smooth surface.

2.      Turn on the Hovercraft then place it on the smooth surface.

3.      Notice the Hovercraft floats above the surface.

4.      Try the Hovercraft out and observe the direction the Hovercraft moves.

5.      Adjust the fan so the Hovercraft moves forward in a straight line.

6.      Cut a piece of thread about half the width of the pan or about 15 cm (6 inches) long.

7.      Tape the thread to the SIDE of the Hovercraft.

8.      Hold the thread to the side of the Hovercraft. Start up the Hovercraft.

9.      Notice the path of the Hovercraft after the end of the thread is reached. The Hovercraft should move in a straight line, but an outside force (the tension in the string) acted on it. The outside force caused the part of the Hovercraft to change.

10.  Tape the loose end of the string to the floor or center of smooth surface. Try to get the Hovercraft to move in a CIRCLE at the end of the string. This is a special type of motion called CENTRIPETAL MOTION. The tension in the string is the CENTRIPETAL FORCE. The force is TOWARD THE CENTER of the curve. If the force from the string were not present, the Hovercraft would move in a straight line because of INERTIA.

11.  Use your finger to hold the string in place as the Hovercraft moves in a curve.

12.  Release the string and notice how the Hovercraft moves. It moves in a straight line. It does NOT move away from the center of the curve. When an object has a centripetal force acting on it, it moves in a curve. As soon as the centripetal force is gone, the object moves in a straight line (this is because of INERTIA, Newton’s First Law of Motion).

Conclusion

1.      Explain to tell when a force acts on an object.

2.      Explain to recognize an unbalanced force.

3.      Explain how you know the string pulls IN instead of pushing OUT on the Hovercraft.

4.      Draw a picture from above showing how the Hovercraft moves forward if the string is NOT held down by tape or a finger.

5.      Draw a picture from above showing how the Hovercraft moves forward if the string is held down by tape or a finger.

6.      Draw and label the centripetal force acting on the Hovercraft when the string is held down.