Teacher Notes


Liquid AccelerometerDemonstration Kit
Publication No. 13919
IntroductionThe surface of a liquid often forms a nice visualization of the external forces acting upon the liquid. In this demonstration, a tray of water is spun in a circular fashion to see what happens to the surface of the liquid. Concepts
MaterialsFood coloring (optional) Water Floating object, ball or cork (optional) Liquid Accelerometer Demonstration Apparatus* *Materials included in kit. Safety PrecautionsAlthough this demonstration is considered nonhazardous, please follow all normal laboratory safety guidelines. DisposalWith proper care, the demonstration device can be used indefinitely. The accelerometer should be cleaned and dried prior to storage. Prelab PreparationFill the demonstration apparatus with water to a depth of approximately 2". If desired, add a few drops of food coloring to the water to make the water more visible. Conduct a practice run of the demonstration before class to test for leaks and proper operation. Procedure
Teacher Tips
Correlation to Next Generation Science Standards (NGSS)^{†}Science & Engineering PracticesUsing mathematics and computational thinkingDisciplinary Core IdeasMSPS2.A: Forces and MotionMSPS3.A: Definitions of Energy HSPS2.A: Forces and Motion Crosscutting ConceptsEnergy and matterPerformance ExpectationsMSPS11: Develop models to describe the atomic composition of simple molecules and extended structures. DiscussionUniform circular motion results when the net force acting upon a mass moving at a constant speed changes direction in such a way that the mass is deflected into a circular path. The force is always acting at a right angle to the direction that the mass is moving. The force causing this reaction is called the centripetal force. {13919_Discussion_Figure_2_Centripetal force directed toward center of circle perpendicular mass movement}
Uniform circular motion can be analyzed using vector diagrams to derive the equations for centripetal acceleration and centripetal force.
{13919_Discussion_Equation_1}
Note that the centripetal force is proportional to the square of the velocity. Thus, doubling the speed of a moving object will require four times the centripetal force to keep the motion in a circle.The characteristic parabolic curve observed in the accelerometer device is a reflection of the centripetal force gradient that is set up with the rotary motion. The greatest F_{c} is found at the outside of the circle where the radius (r) is the greatest. For the F_{c} to be greater, the water, which can flow easily, is “piled up” in the gradient mathematically depicted by the parabolic curve. {13919_Discussion_Figure_3_Parabolic curve generated by spinning accelerometer}
