Vectors: Lifting a Bowling Ball
Initial Publication Date: October 25, 2008
Summary
In this activity you have students experience and then physically analyze two different methods of lifting a bowling ball. Students must use and understand vectors to create a useful free body diagram and explain why one person can lift the bowling ball easier than two people (note: the two people are lifting the ball at a large angle from the normal).
After completing this activity the students will be able to demonstrate the use of free body diagrams and vector analysis - in particular breaking vectors into components.
CollapseLearning Goals
- Vector analysis
- Free body diagrams
Context for Use
This activity can be used with any grade level. Students must be able to see the bowling ball and string so they analyze the situation. Large lecture classes with a suitable setup (camera or large setup) works.
We use a bowling ball that has an eye bolt mounted in it with a cable that has loops on each end to facilitate the lifting. However, any suitable mass and rope may be used. A smaller scale version could be passed out to student groups so everyone could experience the demo.
We use a bowling ball that has an eye bolt mounted in it with a cable that has loops on each end to facilitate the lifting. However, any suitable mass and rope may be used. A smaller scale version could be passed out to student groups so everyone could experience the demo.
Description and Teaching Materials
This activity starts with an interactive demo. A bowling ball (or other large mass) is lifted using two different methods.
- Invite a smaller student to pick up the bowling ball directly. A string is attached to an eyebolt in the bowling ball to facilitate this action. After the student has picked up the ball ask the class to draw a diagram and analyze the forces. Have the students calculate the force required to lift the ball. Ask the students if it would be easier for two students to lift the ball.
- Now have two students lift the ball. Thread a long cable (or rope) through the eyebolt and have the students stretch out the cable. The challenge is to have the students lift the bowling ball to waist level without having their hands move much above their waist level. This is a much harder task (most students can not lift the ball to their waist keeping their hands at waist level). Now have the students draw a diagram and analyze the forces. What force is required to lift the mass now?
Trigonometry, Work done (in different directions)
Teaching Notes and Tips
Have the two people hold the cable (rope) at waist level. They will have to apply a large force to the cable (rope) to lift the bowling ball. Warn them not to release the cable (rope) suddenly.
To add interest use a smaller person to lift the ball directly and two burly students to "try" to lift at an angle.
To add interest use a smaller person to lift the ball directly and two burly students to "try" to lift at an angle.
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Assessment
You can evaluate student work either directly or have them turn in their diagrams and analysis.