“Reaction to Gravity”
Student Learning Objective:
· Use metric measurements
· Compare your reaction time to the typical reaction time of an adult.
Materials (per pair of students): Standard Ruler with both English & Metric
Introduction:
The force of gravity causes objects to be accelerated downward, toward the center of our Earth. The acceleration due to gravity is 9.81 m/s/s every second or 21.9 mph every second. The rate at which an object is accelerated, gains speed, results in that object falling a certain distance in a certain amount of time.
Preliminary Questions:
A. The dashed lines in the image above show the distance the ball falls each tenth of a second.
a) What happens to the distance the ball falls during these equal time increments?
b) How would you describe the motion of the ball?
B. Look at the ruler. Hold it in your hand. When your partner drops the ruler through your open hand, at which measurement on the ruler do you think you will be able to grasp it?
Procedures:
You will be attempting to catch a ruler as fast as you can after your teammate drops it.
1. Read all team procedures (2-6) before you begin any experimenting. Then carefully read each step as your team completes this activity. Take turns, alternate, using the materials and making observations.
2. Look at the metric ruler below and identify the centimeters on your team ruler.
3. Each person in your group will attempt to grasp a ruler as it falls; record only your own data, and only record successful attempts. One person will hold the top of a ruler so that the ruler hangs down vertically, with the 0 measurement at the bottom and the highest number measurement on the ruler at the top. Place your index finger and thumb at the bottom edge of the ruler as if you are about to pinch the ruler.
Procedure 3 Procedure 4
4. The person who is holding the top of the ruler, so that it hangs down vertically just above your fingers, will allow the ruler to drop without warning. You will then pinch the ruler as fast as you can. Determine the distance the ruler has fallen in centimeters by looking at the measurement where you pinched your fingers together. Record this measurement. If you do not catch the ruler and it falls to the floor, do not record the attempt; start again.
5. Repeat procedures 3 and 4 until you have a total of five measurements recorded.
6. Change roles so that your partner has a turn to catch the ruler and record measurements.
7. Clean up:
· Return the ruler to its designated place.
Analysis & General Questions:
1) Calculate the average of your measurements - add them together and divide by 5. This is the average distance the ruler traveled while you attempted to grasp it.
2) Compare your reaction, your average distance measurement, with others on your team. Would you characterize your team measurements to be relatively similar or different? Why?
3) A typical reaction distance for an adult is 30 centimeters. How different is your average measurement from the typical measurement for an adult? What factors may account for the differences?
4) In science there is always some amount of error involved with the experiment. What were the errors in this experiment?
5) What made the ruler drop once your partner let go of it?
6) Was the ruler falling at a constant speed as it was released? Explain.
Ciardi, T Reaction to Gravity 2