Teacher Notes



Teacher Notes
Publication No. 12267
Centripetal ForceStudent Activity KitMaterials Included In Kit
Handle tube
Paper clips, 2 Rubber stopper, twohole String, 1.5 m Washers, 20 Additional Materials Required
(for each lab group)
Balance, 0.1g precision Graph paper Meter stick Stopwatch or clock with second hand Safety PrecautionsThis lab is best conducted outdoors, in an open gymnasium or other large open area. All students should wear safety glasses whenever anyone is conducting the experiment. You might check each experimental setup before the twirling begins. Have students spread out as much as possible. Please follow all laboratory safety guidelines. DisposalAll materials in the kit may be reused many times. Teacher Tips
Correlation to Next Generation Science Standards (NGSS)^{†}Science & Engineering PracticesDeveloping and using modelsAnalyzing and interpreting data Planning and carrying out investigations Using mathematics and computational thinking Disciplinary Core IdeasMSPS2.A: Forces and MotionMSPS2.B: Types of Interactions MSPS3.B: Conservation of Energy and Energy Transfer MSPS3.C: Relationship between Energy and Forces HSPS2.A: Forces and Motion HSPS3.A: Definitions of Energy Crosscutting ConceptsPatternsCause and effect Systems and system models Scale, proportion, and quantity Energy and matter Performance ExpectationsMSPS21: Apply Newton’s Third Law to design a solution to a problem involving the motion of two colliding objects. Sample DataPart II. Measuring the Force {12267_Data_Table_1}
Answers to QuestionsPart I. Feeling the Force
Recommended Products


Student Pages


Student PagesCentripetal ForceIntroductionHave you ever been on a human centrifuge at an amusement park? You can certainly feel the tremendous force being imposed upon your body as you travel in a circular fashion—so much force that when the floor drops away, you are pinned against the wall! Concepts
BackgroundCentripetal force is the “center seeking” force that makes an object move in a circle. According to Newton’s first law, when an object is in motion, it will remain in motion unless acted upon by an unbalanced force. This means an object will travel in a straight line at a constant speed as long as no outside force is acting on it. In order for an object to move in a circle, an inward force is needed. For example, imagine a rubber stopper being whirled around on the end of a string. The hand holding the string exerts an inward force (centripetal) on the rubber stopper (see Figure 1). If the string were to break, the stopper would fly outward in a straight line. {12267_Background_Figure_1}
The mathematical expression for centripetal force is the same as for any other force, based on Newton’s second law of motion:
{12267_Background_Equation_1}
where
F is the force (N) {12267_Background_Equation_2}
where
a is the centripetal acceleration Now if we substitute Equation 2 into Equation 1, centripetal force can be expressed as Equation 3. {12267_Background_Equation_3}
Notice that in order to solve for the centripetal force using Equation 3, the mass and velocity of an object, as well as the radius of its circular path, must be known. The mass can easily be measured using a balance, and the radius can be measured with a meter stick. But how can the velocity of the object be measured? The typical equation for calculating the average speed (v) of an object can be used to determine the velocity.
{12267_Background_Equation_4}
Now the question is, how can you find the distance around a circle? When an object makes one complete revolution, it travels a distance equal to the circumference of a circle, 2πr. The time it takes for one complete revolution around a circle is known as the period, T. Therefore, for objects moving in a circle, the velocity can be expressed as Equation 5.
{12267_Background_Equation_5}
where
v is the velocity (m/s) Experiment OverviewThe purpose of this lab activity is to determine the relationship between the velocity and centripetal force of an object moving in a circle. Materials
Balance, 0.1g precision
Graph paper Handle tube Meter stick Paper clips, 2 Rubber stopper, twohole Stopwatch or clock with second hand String, 1.5 m Washers, 20 Safety PrecautionsThe very nature of the motion in this activity makes it potentially dangerous. Use caution when twirling the rubber stopper. This lab is best conducted outdoors, in an open gymnasium or other large open area. Wear safety glasses whenever your group or anyone else is conducting the experiment in the area. Please follow all laboratory safety guidelines. ProcedurePart I. Feeling the Force
Student Worksheet PDF 