Review Linear Motion, Acceleration, Acceleration Due to Gravity

PPT Dollar Drop

Developer Notes

Version / Date / Who / Revisions
04 / 8/6/03 / sc / · Deleted references to graph of varied finger distances
· Added explanation of opening activity- do as POE
· Added explanation of exploratory activity & discussion
· Revised student pages to reflect exploration
· Changed title
05 / 2003/09/03 / dk / · added reading and exercises
06 / 2004/06/28 / Sc / · Edited to fit new sequence
· Reading is now also included in Electric cars, I don’t know where it best belongs.

· DK - This still needs improvement in the teacher's section on the goals of the activity and teaching experimental controls, variables, what to measure, etc.

Goals

· Review linear motion, acceleration, acceleration due to gravity

· Introduce physiology of reaction time

· Have students develop their own experiments

Concepts & Skills

Area / Concept
Science / Experimental controls

Time Required

A few class periods

Warm-up Question

Presentation

This activity is a good review of previous concepts, like acceleration and gravity, that student’s need to recognize and remember in order to solve the problem. We are using what we have already learned in physics to explore physiology! From this activity, we can further explore the nervous system, and the physics involved with how the nervous system works. The students also have a chance to design their own experiments completely from scratch!

To start the activity and get the students interested, take out a dollar bill and demonstrate dropping it and catching it with your index finger and thumb (it’s easy for you to catch it yourself). Then ask for a volunteer. Tell your volunteer that if he or she can catch the dollar then he or she can keep it. Hold the dollar bill between the volunteer’s index finger and thumb with the face of the dollar even with the fingers. Make sure the dollar is not touching the fingers. Have the rest of the class predict if the volunteer will catch it or not (do a POE). Most likely your volunteer will not catch the dollar (however some of these young kids have really quick reaction times!). The rest of the class can start to think about why he or she could not (or could) catch the dollar.

Ask the class, “How could you measure how long it takes to catch something dropped, like the dollar bill.” Have them work in groups to brainstorm ideas and design an experiment using any materials you make available (such as meter sticks, rulers, index cards, stopwatches, etc). After the groups run their experiments, have a class discussion about each group’s data and experimental design. Discuss sources of error and how the groups can compare results. This should lead to the students realizing the need for certain controls and a set procedure for the entire class. Scientists need consistent, repeatable results that they can compare.

It's hard for the students to give up stopwatches. Have a few students try to start and stop the stopwatch as fast as they can and compare the times they get to the times they found on their original tests. The numbers will be similar, so were they timing the catch or how fast they can turn the stopwatch on and off?

Have the class work on developing an improved design, leading them, if necessary, to dropping a ruler. A ruler is heavy enough to fall straight, and it has built-in markings. They can drop the ruler and measure the distance it fell before it was caught Hopefully, the students will remember that the ruler is accelerating and that they can use the d = 1/2 at2 formula to calculate the time it took the ruler to fall.

Important controls that should come out of the discussion include:

· finger spacing should be consistent

· the ruler should always start at the same point

· the ruler should be dropped straight

· the catcher shouldn't know when the ruler will be dropped

· the catcher's hand should be constrained so it doesn't move

· there should be more than one drop/catch for each student (3? 5?)

· the units used for measurement should be consistent

There may be other ideas:

· the catcher should use their dominant hand

· the windows should be closed to stop wind

· everyone should use the same type of ruler

One of the points of this exercise is how difficult it is to control even a simple experiment, like dropping and catching a ruler - there are a lot of factors to consider. Scientists need to think about controls, sources of error, and what they can measure whenever they are designing or running an experiment.

When all the groups have finished collecting data using the ruler, compare the data as a class. Why are there variations in the data? Is it because of the falling ruler? Or is it because of the person catching it? From physics, we know that all objects on Earth have the same acceleration due to gravity, so it can’t be the ruler! It must be the person catching it! What is involved physiologically?

Note: The following student activity pages do not have to be handed out to the students.

Assessment

Embedded assessment: Distance measurement and data recording.
Can the students read a centimeter ruler?
Do they remember to use SI units and not English units?
Are the appropriate units used and recorded?

Writing Prompts

Relevance

Answers to Exercises

Answers to Challenge/ extension

Background
Problem

How could you measure how long it takes to catch something dropped, like the dollar bill?
Materials

Anything available from your teacher (like meter sticks, stopwatches, paper, index cards, rulers, paper clips, string, etc.).

Procedure

1. Write out the steps that you will take to conduct your experiment.

2. Conduct your experiment and record your data.

Some questions to keep in mind:

· How many times should I repeat the data collection?

· What are some important things to keep the same (control) in each trial?

· What is a good way to organize the data?

Summary

1. Can you easily compare your data with another group’s data?

2. How can each group collect data that is easy to compare?

Reading

What is science? It's many things. Mostly, it is the search for patterns in the natural world. Science requires people working, sharing ideas, and building on each other's knowledge. Here's a list of what science is:

§ People (scientists)

§ Communication (including a common language)

§ Accumulated knowledge (what we know)

§ Common methods (how we work)

When people find a pattern in something, they think they understand it. Better yet, if they can predict what will happen in the future, they really think they understand it. The test of knowledge in science is experiment. Scientists test their ideas. If an idea is not testable, it is not scientific.

So scientists make predictions and test them to see how well they understand. A prediction may turn out to be right, but just being right doesn't prove you understand it - you might be right for the wrong reason or maybe it was a lucky guess. A testable (scientific) idea is one that can be proved wrong. In Chicago, the amount of ice cream sold and the number of murders always increase and decrease together. Does eating ice cream lead to violence? No, they both increase during hot weather. As Einstein said, "No number of experiments can prove me right; a single experiment can prove me wrong."

What makes a good experiment? A good experiment is as simple as possible, so other people can understand and repeat it. Sources of error are minimized. In the simplest experiment, everything stays the same except for one thing that is changed on purpose. Then, if other things change, it is probably because of the one thing that was changed. The things kept the same are called controls. The one thing that is changed is the independent variable. The thing that changes is the dependent variable. If you drop a ball from different heights to see how high it bounces, the height from which you drop it is the independent variable, and how high it bounces is the dependent variable. Using the same kind of ball and the same kind of floor are controls.

In order for scientists to communicate, they need to share a common language. Latin was the language of science, but the most common language used today is English. There are many words with special definitions that scientists use so they can be clear with each other. Scientists also use a lot of mathematics. Incredibly, the natural world can often be described mathematically! It is one of the great mysteries of the world - for example, why would a ball flying through the air be describable by an equation (almost) as simple as y = x2?

Scientists prefer to express their findings in numbers, or quantitatively, because numbers are easy to compare and manipulate, but not everything can be expressed in numbers. Many things are better described in words, or qualitatively. Most of the time scientists use both qualitative and quantitative descriptions. Describing a fruit as round and orange is qualitative. Describing it as having a diameter of 0.08 m and a mass of 0.3 kg is quantitative.

Scientists also need to use consistent measurements so they can compare their data. Long ago, people used measurements like foot, hand, span, and cubit to measure distance (the height of a horse is still measured in hands). Those measurements are all taken from the human body, but they vary from person to person. Now we use the metric system, which uses meters, kilograms and seconds (mks).

One other very important aspect of science is honesty. Scientists must be honest. If they aren't, they don't contribute to the growth of scientific knowledge, and they can harm people. In fact, scientists are always verifying each other's work. If a scientist ever lies and is found out, they will never be able to work as a scientist again, because no one will trust them.

Physics is the most basic science, studying what matter or "stuff" is, and how it interacts with other matter. Originally, physics was the name for all of natural science (as opposed to metaphysics, the study of things beyond physics, like philosophy and religion). As the knowledge in science has grown, parts of physics have become their own fields, like chemistry, biology, and physiology.

Exercises

Identify the independent and dependent variables in these scenarios.

Plants in the sunlight grow taller than those in the shade.
Dogs pant more when it is hot outside.
Some cows eat grass and some eat corn. Cows that eat corn have a higher fat content than cows that eat grass.
Fish often will move into an area where other fish are present, but not into an area where they don’t see other fish.
In years when there is not very much to eat, birds will lay fewer eggs than usual.
In one research study, more mice got cancer when they were fed a certain chemical than mice that did were not fed the chemical.
In one research study, more worms died when they were kept in still water than when they were kept in running water.
In one research study, fish eggs exposed to caffeine hatched earlier than fish eggs that were not exposed to caffeine.

Read each of the following descriptions of scientific studies. Underline the parts of the study that you feel may cause error. Describe how you would change the study to fix that problem.

Dr. Jones studied cows. He wanted to know if cows gain more weight on a diet of grass or a diet of soybeans. He put twenty cows in each group. The cows in the grass group were all males and the cows in the soybean group were all females. He fed each cow two pounds of food per day. He weighed the cows for the first time after they had been eating the special diets for a month. He weighed them once a month for six months after that. At the end of the study, he concluded that cows that eat grass gain more weight.

Dr. Martinez studied bats. She wanted to know if bats prefer to eat apples or plums. She cut the fruit into pieces. She wanted to put an equal amount of fruit in each dish, but plums are smaller, so she cut the plums into 1 centimeter pieces and the apples into 3 centimeter pieces. She left the fruit out in dishes overnight in the nature preserve and counted the fruit pieces that were left in each dish the next morning. She concluded that bats prefer plums because there were fewer pieces of plum left in the dish.
Dr. Wong studied worms. He wanted to know if worms living in sand grow longer than worms living in mud. He employed two graduate students, Jason and Marla, to measure the worms. Jason measured the worms in the sand, and Marla measured the worms in the mud. Because Marla’s measurements were on average a little longer than Jason’s, Dr. Wong concluded that worms grow longer when they live in mud.
Dr. Francis studied tiger sharks. She wanted to know if male sharks have longer teeth than female sharks. She caught 5 male sharks and 5 female sharks, and measured their body length and their teeth. The male sharks were between 3 and 3.5 meters long and the female sharks were between 3.5 and 4.5 meters long. Overall, the male sharks had teeth that were between 5 and 6 centimeters and the females had teeth that were between 6 and 8 centimeters. Dr. Francis concluded that female sharks have longer teeth than male sharks.
Dr. Smith studied orchid plants. She wanted to know if one species of orchid has more chlorophyll (the green pigment in plant leaves) than another. To save time she ran her pigment tests at the same time using two different spectrometers (machines that test the amount of pigment). Her test showed that orchid species A has slightly more chlorophyll than orchid species B.

Challenge/ Extension

Make a list of 6 things that you think might influence how quickly an individual can react to an event such as catching a falling object. Explain why you think these factors would positively or negatively influence how quickly someone can catch a dropped object.
Vocabulary