“Falling in Air”
Student Learning Objectives:
· Observe heavy an light falling objects in air
· Identify trends that may account for differences in time to fall
Materials (per team): 1 Feather
1 Pencil Eraser
1 Golf Ball
1 White Practice Ball (whiffle ball)
1 Yard Stick or Meter Stick
Introduction:
The acceleration due to gravity is the same for every mass. What is different for each mass is the amount of air resistance it experiences. For an object falling in air, the net average acceleration is a combination of the downward acceleration due to gravity and the upward acceleration caused by air. The downward acceleration due to gravity is constant, the number does not change. The upward acceleration caused by air resistance (friction with the air) changes; air resistance increases when speed increases. Since objects fall faster and faster, the air resistance increases while the object is falling. Additionally, air resistance depends on surface area.
Preliminary Question:
A. If there was no air, what would the acceleration be for each object?
B. Define surface area. Which of your objects has the largest surface area? Explain what causes this object to have a large surface area.
Feather Pencil Eraser Golf Ball Practice Ball
Warning: Everyone should be aware of where feet and toes are when objects are being dropped.
Procedures:
You will be dropping 4 objects from a measured height.
1. Read all procedures (2-7) 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. Pick up each object, hold it, and look at it. Predict the order the objects will hit the floor by rank ordering them 1st to hit to 4th to hit. Record your prediction. Your predication can be different from others on the team.
3. Use the yard stick (or meter stick) as a guide to ensure that every drop is from the same distance. Have one person stand, holding the yard stick such that the yard stick is resting on the floor and is vertical.
4. Hold the feather and the pencil eraser near the top of the yard stick, count down from 3, and release them at the same time while others on your team watch to see which hits the floor first. Repeat this at least 3 times to ensure that your results are consistent. Record which object tended to hit the floor first. If they hit at the same time every time, then record that it was a tie.
5. Hold the golf ball and the practice ball near the top of the yard stick, count down from 3, and release them at the same time while others on your team watch to see which hits the floor first.
Repeat this at least 3 times to ensure that your results are consistent. Record which object tended to hit the floor first. If they hit at the same time every time, then record that it was a tie.
6. Discuss a plan to complete the experimental rank ordering of your objects, from 1st to hit to 4th to hit. If there are different ideas, listen to all ideas, and come to consensus. Write the plan.
7. Follow your team plan to determine the rank order in which objects hit the floor from 1st to hit to 4th to hit. Record the results of your experiment.
Analysis & General Questions:
1) Compare your predicted order for objects to hit the ground to the experimental order. What may account for any difference between your prediction and the actual results?
2) Based on your experiment, which of these objects was traveling the fastest when it hit the floor? Explain why.
3) In the absence of air, would there be any difference in the rate of descent for your objects? Explain.
4) Predict the order the following objects would hit the floor by rank ordering them 1st to hit to 4th to hit. Explain why you ordered them this way?
a) Flat sheet of notebook paper
b) Basketball
c) Empty water bottle
d) Penny
Ciardi, T Falling in Air 2