For this experiment, you will need:

• 1 meter of string
• A student’s keys (or another mass)
• Two people

Thread the keys onto the string and position them at the center.

Give one end of the string to each person.

Each person should pull on his or her end of the string and try to make it perfectly horizontal.

1. Draw a vector diagram of the experiment.
2. Why can’t you pull the string hard enough to make it perfectly horizontal?

Variations of this Seat Experiment:

• Use a thick, heavy rope that is 7-10 meters long, and no mass for the center. Have two "strong" students volunteer and ask them to hold the rope at waist level and pull as hard as they can. Note that without a mass at the center, the rope cannot be made horizontal.
• Same rope, have several students pull on each end at waist level.
• Same rope, two students on each end. Have the students pull the rope tight. Ask another student push the center of the rope down to the ground. The students on the ends should keep pulling horizontally and try not to let the rope touch the ground. Note that this is not difficult for the student in the middle to get the rope to the ground.

Reference:

Berry, Donna A. (1986). A Potpourri of Physics Teaching Ideas. American Association of Physics Teachers, College Park, MD

Laws, Priscilla W. (1997). Workshop Physics Activity Guide. John Wiley & Sons, Inc., New York, NY

 

Instructor’s Notes

 

Answer Key:

1. Forces Exerted By Students

String

Mass or Keys

Weight

 

2. Because the string is pulled nearly horizontally, it has little or no vertical component to balance the downward force due to gravity (the weight) of the keys (or mass), and this is why it can’t be pulled tight enough to make it completely horizontal.

 

 

[Back to Seat Experiment Index] [Tahmineh Singleton]