Can quarters and feathers fall at the same speed?

Falling Feather

Prove to yourself that Galileo was right!

In a famous demonstration, Galileo supposedly dropped a heavy weight and a light weight from the top of the Leaning Tower of Pisa to show that both weights fall at the same acceleration. Actually, this rule is true only if there is no air resistance. This demonstration lets you repeat Galileo's experiment in a vacuum.

A clear, plastic, rigid-walled tube with at least a 1 inch (2.5 cm) inner diameter and at least 3 feet (90 cm) long. Available at your local plastic store. (Longer tubes show the effect more clearly.)

A solid rubber stopper and a one-hole rubber stopper to fit in the ends of the plastic tube.

A section of copper tubing about 4 inches (10 cm) long that fits tightly in the hole in the rubber stopper (glass tubing can be used if care is taken).

A thick-walled flexible plastic or rubber vacuum tubing about 6 feet (180 cm) long.

A coin and a feather (or a small piece of paper).

A vacuum pump (use a regular lab vacuum pump if available; if not, use a small hand pump such as Mityvac®).

2 hose clamps.

Adult help.

(30 minutes or less)

Insert the solid stopper firmly into one end of the plastic tube. Put the coin and feather in the tube. Push the copper tube through the one-hole stopper, and firmly insert the stopper in the other end of the plastic tube. Push the vacuum tubing over the copper tube and secure it with a hose clamp, if needed. Attach the other end of the vacuum tubing to the pump; again, use a hose clamp if needed.

(15 minutes or more)

Invert the tube and let the objects fall. Notice that the feather falls much more slowly than the coin. Now pump the air out of the tube and invert it again (the pump can remain attached while you invert the tube). Notice that the feather falls much more rapidly than before - in fact, it falls almost as fast as the coin. Let the air back into the tube and repeat the experiment. (Try to avoid rubbing the wall of the tube; otherwise, static electricity may make the feather stick to it.)

Galileo predicted that heavy objects and light ones would fall at the same rate. The reason for this is simple. Suppose the coin has 50 times as much mass as the feather. This means that the earth pulls 50 times as hard on the coin as it does on the feather. You might think this would cause the coin to fall faster. But because of the coin's greater mass, it's also much harder to accelerate the coin than the feather - 50 times harder, in fact! The two effects exactly cancel out, and the two objects therefore fall with the same acceleration. This rule holds true only if gravity is the only force acting on the two objects. If the objects fall in air, then air resistance must also be taken into account. Larger objects experience more air resistance. Also, the faster an object is falling, the more air resistance it feels. When the retarding force of the air just balances the downward pull of gravity, the object will no longer gain speed; it will have reached what is called its terminal velocity. Since the feather is so much lighter than the coin, the air resistance on it very quickly builds up to equal the pull of gravity. After that, the feather gains no more speed, but just drifts slowly downward. The heavier coin, meanwhile, must fall much longer before it gathers enough speed so that air resistance will balance the gravitational force on it. The coin quickly pulls away from the feather.

The terminal velocity of a falling human being with arms and legs outstretched is about 120 miles per hour (192 km per hour) - slower than a lead balloon, but a good deal faster than a feather!

What materials block radio waves most effectively?

How Do Different Obstacles Affect Radio Waves?

Ross .S

SOAR 6^th 1998

PURPOSE

The purpose of this experiment was to find out which materials block radio waves and thus cause the most interference for remote control devices.

I became interested in this idea because I wanted to know what objects I have in my house that would cause interference to my R/C car.

The information gained from this experiment will help if someone is using remote control robotics or devices. It may be useful for scientific reasons, remote exploration as well as recreation. This experiment will benefit all those by determining which materials a R/C car user should avoid transmitting through.

HYPOTHESIS

My hypothesis is that the cement (brick) will give the least interference and that the glass will have the most interference.

I base my hypothesis on a book series called Elements; the AEE homepage and an encyclopedia called Science & Technology. I also base my hypothesis on my own educated guess that glass has very compressed molecules and a reflective surface, and brick has cracks and spaced out molecules.

EXPERIMENT DESIGN

The constants in this study were:

The obstacle used to obstruct the radio wave

The distance for the radio wave to travel

The distance for the car (receiver) to travel

The amount of time it took the car to travel from the beginning court to half court

The manipulated variable was the amount of time it took the radio wave to pierce the obstacle (the wood, glass and brick). Then hit the receiver and cause the remote control car to move and then hit the centerline at half court.

The responding variable was the amount of time it took the car to start up from the beginning court line to then drive and arrive at the half court line.

To measure the responding variable I used a stopwatch to determine how much time it took the car to go from the beginning of the basketball court to the center of the basketball court.

MATERIALS

QUANTITY ITEM DESCRIPTION *C/A= Commonly Available

*C/A Cement (brick)

*C/A Wood

*C/A Glass

1 Stop-watch

1 27 MHz remote control car

24 AA alkaline batteries OR batteries

6 9v batteries OR

1 rechargeable 9v batteries

PROCEDURES

1. Place remote control car's (receiver) back wheals on the very edge of the beginning line of the basketball court.

2. Get someone (friend, family) to hold the remote control (transmitter) and stand outside the door of the gymnasium.

3. Have stopwatch set to proper setting.

4. Get to eye level with the mid-court centerline or where the car will stop.

5. Shout out a signal, like "GO!" then immediately start the stopwatch.

6. When the car touches the beginning on the mid-court line stop the stopwatch and give a signal to stop, like "STOP!"

7A. Place 4 new AA alkaline batteries in car OR

7B. Recharge 4 AA alkaline batteries from car then replace.

8A. Place 1 new 9v battery in remote control OR

8B. Recharge 1 9v battery then replace.

9. Close the door of gymnasium, with assistant remaining behind the door, to give you the material of glass.

10. Repeat steps 1 - 8B; be sure to replace step 2 with step 9.

11. Have assistant stand behind the boy's locker room wall to give the material of cement.

12. Repeat steps 1 - 8B; once again replace step 2 with step 11.

13. Have assistant stand outside the closed wooden door (separating the transmitter from the receiver) to give material of wood.

14. Repeat steps 1 - 8B; replace step 2 with step 13.

15. Repeat all steps (including steps 11 and 13) at least once more to confirm previous results.

RESEARCH REPORT

INTRODUCTION

My project is called, "How Do Different Obstacles Affect Radio Waves?". I learned about the different types of radio waves, and also learned about their many uses.

Types of Radio Waves

There is a large amount and Varity of radio waves, the two most radio waves would have to be AM and FM. AM (Amplitude Modulation) transmits by being transmitted into the air, it is bounced of the ionosphere and then reflected back to an antenna of a radio or other receiver. Unfortunately, this makes the radio wave more prone to interference like lightning or interference by other radio waves. FM (Frequency Modulation) is sent on a ground wave. This ground wave spreads out across the ground to reach radios. Sometimes when you drive in hilly areas, the FM wave is blocked out and the signal becomes mixed with static. The FM radio wave cannot be reflected off the ionosphere because the signal pierces through the earth's atmosphere and travels through space.

Uses of Radio Waves

The uses of radio waves are vast and extreme. One use, being the most obvious, is entertainment. The standard AM FM radio can cover 53-171 kHz with FM and 88-108 MHz is used by AM. A TV uses both AM and FM to broadcast their signals to televisions all over the world. One other popular use is recreation. Remote control models are a common hobby, whether you build them or just by ones to race others. Remote control models/toys are usually brodcasted on frequencies from 1-80 MHz. \par Another use is the exploration of space. A radio telescope uses FM signals to send out in space to record the distance of objects. When the signal hits something, it bounces back and is recorded on a computer. The radio wave can be used to explore the earth too. Small remotely controlled, unmanned submarines have been sent to the depths of the oceans with cameras to record things that would be extremely expensive find out. Remote controlled robots on land can be sent into volcanoes or other hostile environments to gather information. \par The largest and most important use is communication. Walkie-talkies are used by policemen, firemen, the army and some have even been made for a more kind of family use. A more recreational communication is HAM radio; HAM radio is a sort of amateur radio. Although many of the people who use it are far from amateur for they can reach people all across the globe.

The Basics of an R/C Car

The more common toy-type remote control car uses the same frequencies as other more model-type cars. The two frequencies made most available by the toy-type R/C's are 27 MHz and 49 MHz. The common toy-type R/C uses a simple kind of direct radio wave. When you press a button or move a lever on the transmitter, it sends a precise signal to one of the R/C car's many carefully tuned servos. The common car uses a rather simple motor that is battery powered. The model car is almost the same as the common one. With the exception that their motors are much more advance and can even be gasoline powered. Also, the advance car may have more controls, thus having more servos.

SUMMERY

The two main radio waves are AM and FM. Radio waves are used for communication, recreation, the exploration of space and the exploration of our earth. A remote control car usually will use a simple radio wave transmitted by the controls to function.

RESULTS

The original purpose of this experiment was to see which materials, out of wood cement and glass, conducted the most interference against radio waves. Hopefully the materials would cause the loss of speed in the car (receiver).

The results of the experiment were surprising. I was a little unhappy with how the accuracy of the experiment was. For example the car did not always go completely straight due to the crude way of having to align the car's wheels with the simple line on the basketball court. Another example would probable be the amount of hesitation that was present, even being off by about a hundredth or tenth of a second would have to be noted. I believe that the start of the stopwatch and the starting of the car were not started right on the mark.

See the table and graph below.

CONCLUSION

My hypothesis was incorrect. The wood offered the most interference, and then the glass and the brick offered the least interference to the radio waves. The results indicate that this hypothesis should be rejected. I thought that the glass would have the biggest results on the radio waves, but in actuality the wood offered more interference and the brick offered the least.

Because of the results of this experiment, I wonder if the way I chose to measure the material's interference on the radio waves was the best choice. If I were to conduct this project again I would definitely rethink the choice of car and choice of experiment on the radio waves.

How to make your own telegraph machine.

Talk By Lightning Telegraph

Dot-dot-dot-dot; dot; dot-dash-dot-dot; dot-dash-dot-dot; dash-dash-dash. That’s Morse Code for hello. Named after the American inventor Samuel Morse, Morse code is a system of short dots and longer dashes which represent the letters of the alphabet. Signals are sent by starting and stopping the flow of electricity through a wire.
You can make your own telegraph for sending secret messages to a friend. This project may require a trip to the store, some patience, and maybe a bit of help, but it's well worth it. After connecting all your wires and buzzers, you'll be able to “talk by lightning” (as telegraphy was once called).

Materials

• two pieces of cardboard approximately 20 cm x 10 cm
• two pieces of cardboard approximately 3 cm x 8 cm
• three pieces of wire approximately 19 cm long
• three long pieces of wire (see note)
• one new "D" cell battery
• four thumbtacks
• two lights (see notes)
• wire strippers (or scissors)
• pliers
• tape

Notes
If you want to build this project so you can communicate with a friend/brother/sister in another room, the three long pieces of wire need to be long enough to reach that room. You can also build the telegraph with shorter wires and then replace them with longer wires later.
The lights can be replaced by buzzers or light emitting diodes (LEDs: semiconductors which glow when electricity flows through them; used as power indicators on computers and other electronic gadgets.) All of these are inexpensive and available from Radio Shack or similar electronics stores. The “D” cell battery used in this project is 1.5 volts so it’s important to buy compatible 1.5 volt LEDs, buzzers, or lights (we used a 2.37 volt light bulb which worked fine). If they are not available, don’t worry, you can simply tape two batteries together. Of course, you can mix-and-match: use a buzzer in one room and a light in the other.
Buzzers and LEDs only work if the electricity flows in the correct direction. So you have to pay close attention when connecting them. On the buzzer, the red wire indicates the positive side, and the black wire indicates the negative side. On a LED, the long side usually means positive. You can also look to see if one side has a flat spot. If it does, that is the negative side. The circuit diagram below shows the positive and negative connections.

Instructions

1. Using wire strippers or scissors, remove about 1.5 cm of the plastic insulation from the ends of each piece of wire.
2. We will need to distinguish between the three long pieces of wire. The easiest way to do this is to put a piece of tape on each and letter one A, one B, and one C.


3. Put a bend in each of the two small pieces of cardboard about 2 cm from one end. Tape these pieces to the right side of the larger cardboard pieces. These will be the switches.
4. Tape the battery to the centre of one of the large pieces of cardboard. The positive (knobby) side should be positioned as in the photograph.


5. Tape two of the short wires to the negative (flat) side of the battery. It’s important to make sure the metal from the wire is making contact with the metal part of the battery.
6. Push a tack through the larger piece of cardboard right underneath the cardboard switch.
7. Make a loop in the free end of one of the pieces of wire taped to the battery and hook it around the tack. Use pliers to bend the tack over on the other side of the cardboard so the wire won't slip out.
8. Tape the buzzer to the other side of the large piece of cardboard.
9. Twist the free end of the second wire to the buzzer’s black wire. Make sure the metal parts are touching one another. It’s also a good idea to wrap tape around the twist to make sure it doesn’t come apart.


10. Push a tack up through the underside of the cardboard switch. When you push the switch down, the two tacks must touch.
11. Put a loop in one end of wire A, and hook it around the tack. Use pliers to bend the tack as before.
12. Tape one end of wire B to the positive (knobby) end of the battery. Remember the metal of the wire must touch the metal on the battery.
13. Twist one end of wire C to the red buzzer wire. Wrap tape around the twist.


14. Push a tack through the second large cardboard piece below the free end of the cardboard switch. Put a loop in the free end of wire B and one end of the remaining short wire. Hook both wires around the tack. Use pliers to bend the tack back.
15. Tape the light to the other side of the piece of cardboard as shown.
16. Attach the free end of the short wire to the light.


17. Attach the free end of wire A to the other side of the light.
18. Push a tack up through the underside of the cardboard switch. When you push the switch down, the two tacks must touch.
19. Put a loop in the free end of wire C, and hook it around the tack. Bend the tack back.

That’s it. Pushing down on the switches completes the electric circuit and turns on the light (or sounds the buzzer)
on the other piece of cardboard. If it doesn't work, check your connections: wire has to be touching wire (or tack)
at each connection. If it still doesn't work, try pushing the wires more firmly against the ends of the battery.

One final note. If you are using LEDs, you may find them hard to connect to the wires. The photo below shows
one easy way.



Morse Code

To send a dot, press down and immediately release the switch. A dash lasts three times as long as a dot. A space between letters is the same length as a dot; a space between words is the same length as a dash.

A .- B -... C -.-. D -.. E . F ..-. G - -. H .... I .. J .- - -

K -.- L .-.. M - - N -. O - - - P .- -. Q - -.- R .-. S ... T -

U ..- V ...- W .- - X -..- Y -.- - Z - -.. Period .-.-.- Comma - -..- - Out .-.-. (message done)