Cenco Physics » Science at Home

Balloon Fuse

bpearson — Sat, 06 Feb 2010 20:12:04 +0000

Purpose: Discuss how house fires happen and illustrate a common safety device used to prevent electrical fires — the fuse.

Materials:

6 Volt lantern battery or DC power supply
balloon
tinsel
tape
alligator clip wires (4)
small 6V light bulb
small light bulb holder

Procedure:

Blow up balloon
Tape a piece of tinsel across the balloon. Keep at least an inch of the tinsel free from the tape on both ends as shown in the diagram below.
Make a complete series circuit including the tinsel (balloon fuse) and the light bulb by connecting the positive side of the battery to one end of the tinsel with the alligator clip. Then connect the other end of the tinsel to one end of the light bulb holder with the next alligator clip. Finally, with the third alligator clip connect the other end of the light bulb holder to the negative end of the battery.
The light bulb should light showing that there is current going through the light bulb and the circuit.
Take the last alligator clip and connect one end to one side of the light bulb holder and the other end to the other side.
You have now created a short circuit, or an alternate path for the electricity to flow around the light bulb instead of through it.
The balloon should burst almost immediately.

Explanation:
A short circuit allows a large amount of current to flow though a wire. As the amount of current increases, so does the temperature of the wire. The tinsel is the part that will heat up the quickest, as it heats up it melts a hole in the side of the balloon causing it to burst, just as a real fuse would melt and become disconnected as too much current flows through it.

Reinforcement Activities:
Take a piece of steel wool and place it across the two terminals of the 6.0 Volt battery, the steel wool will heat up and glow orange hot and eventually break, as the steel wool breaks it could fling in different directions, be sure to wear safety goggles, clear the area of anything flammable, and shield the students from any flying debris. This activity shows what happened to the tinsel in an amount of time in which the students can observe the wool heating up. Point out how short circuits can easily start electrical fires

A different and more common electrical home safety device would be a circuit breaker, which contains a bimetallic strip. The strip bends breaking the circuit when it heats up due to too much current flowing through the circuit breaker. The advantage of a circuit breaker over a fuse is that it does not need to be replaced every time it is blown. You can show students how a bimetallic strip works using an hairdryer.

Happy Sad Balls

bpearson — Thu, 04 Feb 2010 15:14:13 +0000

Learning standards covered by this activity:

Major Understanding

5.1p The impulse* imparted to an object causes a change in its momentum*.
5.1r Momentum is conserved in a closed system. (Note: Testing will be limited to momentum in one dimension.)

The above learning standards were taken from the Core Curriculum Physical Setting/Physics, The University of the State of New York – The State Education Department.

Materials:

a set of happy sad balls
wooden mallet
eye screw hook about ¾” in diameter
glue gun
wooden block about 2” x 4” x 12” in size
ring stand
lattice clamp
rod

Procedure:

Cut the happy and sad ball in half.
Screw the eye screw hook into the top of the handle of the wooden mallet so that the eyehook is parallel to the head of the mallet.
Glue half of the happy ball on one end of the head of the mallet.
The half the sad ball on the other end of the head of the mallet.
Once the glue is dry, set up the apparatus as shown in the diagram below.
Pull back the wooden mallet to a certain angle and always use that angle. About 30 to 45 degrees works best, but you may need to play with yours a little bit to see what works best for your set up.
Set the wooden block standing up right in front of the wooden mallet, and adjust the distance from the wooden mallet to the block until the happy ball just barely is able to knock over the wooden block.
You may want to mark were you positioned your wooden block and your apparatus, to make sure nothing moves.
Now you are ready for the demo.
Show your students the happy ball hitting the wooden block and knocking the block over, then flip the mallet around so that the sad ball hits the block this time. Show the students that you are releasing the other end of the mallet from the same angle as the happy side.
This time the block will not tip over.
Have your students come up with some reasons why this happens, you can have them hold the mallet and knock it against the table, they will see that the mallet will bounce from the table on the happy side and will not on the sad side.

Explanation:
Making some simplifications we can use the following calculations to show students the general idea of why the happy ball knocks the block over and the sad ball does not.

Assume that the speed that happy ball hits the block is the same as the speed that the ball bounces off at.

Assume that the speed of the sad ball after it hits the block is zero

J = impulse
p_i= initial momentum of the wooden mallet
p_f = final momentum of the wooden mallet
m = mass of the wooden mallet with the happy sad balls attached
v = the velocity of the mallet just before it hits the wooden block

J = Δp = p_f−p_i

For the happy ball:

J = mv – m(-v)

J = 2mv

* Since momentum is a vector quantity, the initial and final velocities in this case are equal in magnitude but opposite in direction. Therefore the initial velocity has a negative value since it goes in the opposite direction of the final velocity of the mallet.

For the sad ball:

J = mv – m(0)

J = mv

Therefore the impulse of the happy ball is twice that of the impulse of the sad ball. Impulse is force times time, so if we can assume that the time the happy and sad ball are in contact with the wooden block is the same, then we can assume that the average force acting on the block from the happy ball is twice the force applied by the sad ball.

The block is knocked over because there is more force acting on it from the happy ball than from the sad ball.

It is a good discussion for students to analyze how valid these assumptions are, but the simplifications make the math easy for students to understand at a high school level.

Reinforcement Activities:
You can tie many real life examples to this idea of impulse and momentum. For example, if a student was going to get into a car crash and they had a choice of hitting a snow bank or the side of a building, which should they aim for? You can also talk about Karate Chopping a board. If your hand doesn’t make it through the board it hurts more than if you break the board, have the students explain why that is. These questions would be good questions to introduce or follow up the topic.

Have students study conservation of momentum using a ballistic pendulum. Ballistics is used to study the speed of bullets coming out of a gun. This is an excellent example of using Physics in real life. Use a ballistic pendulum to simulate ballistics without firing weapons in your classroom.

Related Products

Happy and Sad Balls – These polymer balls may look the same but they behave differently, making them the ideal choice for demonstrating the coefficient of restitution.
Lattice clamp – for lattice building and rod coupling.
Aluminum plain end support rods – for constructing support lattices.
Aluminum Rods, 1/2″ diameter, 24″ in length
Ring Stand base
CENCO Ballistic Pendulum – using our classic, time-tested physics apparatus, your students can: demonstrate the conservation of momentum, find the initial velocity of the ball, verify the determination of the initial velocity, find the time of flight of the ball, compute kinetic energy, and Investigate projectile motion.
Basic Student Ballistic Pendulum – a classic physics lab with an impressive military history, the ballistics pendulum was invented in 1742 to measure the speed of bullets.

Alka-Seltzer & Balloon Rockets

bpearson — Tue, 02 Feb 2010 14:33:09 +0000

Learning standards covered by these activities:

Major Understanding
5.1q According to Newton’s Third Law, forces occur in action/reaction pairs. When one object exerts a force on a second, the second exerts a force on the first that is equal in magnitude and opposite in direction.

Alka-Seltzer Rocket Materials:

black 35 mm film canisters
Alka-Seltzer tablets
Water
A flat surface that can get messy

Procedure:

Break an Alka-Seltzer tablet into quarters
Put about 1 teaspoon of water into the bottom of the film canister
Drop the tablet in and quickly seal the top of the canister with the lid
Place the canister upside down on a flat surface and wait about 30 seconds
The rocket should launch a meter or two in the air with a loud popping noise

Explanation:
As the Alka-Seltzer mixes with the water it releases carbon-dioxide gas. The gas is confined to a closed space, so therefore builds up a lot of pressure. Eventually the pressure is so great that the top blows off forcing the canister upward. This is a good demonstration for Newton’s 3rd law. For every action, there is an equal and opposite reaction. The gas is pushing up on the top of the canister and the canister is pushing down on the gas.

Balloon Rocket Materials:

Two chairs
Tape
String
Balloons
Soda Straws

Balloon Rocket Procedure:

Set up two chairs about five meters apart
Tie a string to one end of the chair
Blow up a balloon and hold the end closed, do not tie the end
Tape a straw along it’s vertical axis
Thread the string through the straw and tape the other end of the string to the second chair
Let go of the end of the balloon and watch the balloon race to the other end of the chair
You can add some more fun by having the students design their own balloon using construction paper and tape or change parameters such as the amount of air blown into the balloon or the size of the hole that the air is allowed to escape, to see which student get make the best (quickest) balloon rocket

Explanation:
Just like the Alka-Seltzer rockets, the walls of the balloon are pushing in on the gas and the gas is pushing out on the side of the balloon. All the forces balance until you let go of one end of the balloon, and then the escaping air pushes the balloon forward while the air gets pushed back by the wall of the balloon. It’s Newton’s Third Law again!

Reinforcement Activities:
Have students measure the height of a rocket, time of flight, or analyze if the rocket follows projectile motion. Talk about real world situations and how air resistance affects the flight of an object by having the students design their own rockets. Model rockets and water rockets have excellent applications beyond Newton’s third law and are a lot of fun for student and teacher alike.

Measuring the Speed of Light with Marshmallows

bpearson — Sun, 31 Jan 2010 19:47:12 +0000

Learning standards covered by this activity:

Major Understanding

4.3k All frequencies of electromagnetic radiation travel at the same speed in a vacuum.
4.3m When waves of a similar nature meet, the resulting interference may be explained using the principle of superposition. Standing waves are a special case of interference.

Process Skill

4.3 vi Predict the superposition of two waves interfering constructively and destructively (indicating nodes, antinodes, and standing waves)

The above learning standards were taken from the Core Curriculum Physical Setting/Physics, The University of the State of New York, The State Education Department.

Materials

Glass baking dish (or other microwavable baking dish)
8 oz bag of marshmallows
Metric ruler
Microwave oven
Pot holders
Butter (optional)
Toasted rice cereal (optional)
13 x 9 x 2 in pan greased on the bottom (optional)

Procedure

Coat the bottom of the glass pan/microwaveable dish with butter. (This will allow a much easier clean up and will give you the option of creating a tasty snack afterwards.
Evenly spread the marshmallows on the bottom of the glass dish.
Remove the turntable from the microwave so the pan will not rotate.
Place the pan of marshmallows in the microwave and microwave on high until about five hot spots develop in the marshmallows. The hot spots will be where the marshmallows begin to puff up, eventually the hot spots will sink and turn a light brown color.
Remove the glass dish carefully using the pot holders.
Use the ruler to measure the distance between the antinodes of the microwaves in the marshmallows. Record your data.
Look at the tag on the back of the microwave for the frequency of the microwave and record this number as well. This should be about 2500 MHz or 2,500,000,000 Hz.

Optional Procedure (for fun only)

Have the students mix in 3 cups of toasted rice cereal to the melted marshmallows and spread into a baking sheet for a tasty treat!

Data Analysis
Average the difference between the antinodes. The student should get about 6 cm for most microwaves.

The distance between two antinodes is only ½ a wavelength, so to get the total wavelength the student must multiply by 2.

Calculate the speed of light using the formula:
velocity = frequency x wavelength
velocity = (2,500,000,000 Hz)(.12 m) = 300,000,000 m/s

Explanation
Microwaves are a type of electromagnetic wave with a wavelength of about 0.01 cm to 1 meter. Microwave ovens work by setting up standing waves inside the oven that twist the water molecules in the food back and forth until they heat up. Most microwave ovens have a wavelength of about 12 cm. In the picture of the standing wave below you can see the nodes and antinodes of the string which is a visual of what the wave inside the microwave would look like. The highest energy of the wave occurs at the nodes of the wave. This is where the hot spots in a microwave oven occur. Most microwaves have a turn table because the food needs to be rotated to place most of the food in the path of the hot spots. A hot spot occurs ever ½ a wavelength or approximately 6 cm.

Reinforcement Activities
The standing wave demonstrator from Cenco Physics is shown in the diagram above. Since we can not see microwaves, this provides an excellent visual representation of a standing wave and can be purchased through the following the link below.

Have students create their own standing waves and using 2.0 meter long spiral springs. These springs easily produce standings waves when stretched between two students and give hands on learning experiences with wave characteristics.

Pencil Resistor

bpearson — Fri, 29 Jan 2010 19:21:22 +0000

Materials

6 Volt lantern battery or DC power supply
alligator clip wires (3)
small 6V light bulb
small light bulb holder
pencil
razor blade

Procedure

Take a new pencil and shave half of the pencil off the long way so that you expose the graphite center most of the length of the pencil.
Set up a series circuit containing the battery, the light bulb, and the pencil as shown in the diagram below.
Move the end of the pencil along the graphite and the brightness of the light bulb will change.

Explanation
As the length of a conductor increases, the resistance increases. Since the pencil and the light bulb are connected in series. Increasing the resistance of the graphite in the pencil will increase the resistance of the whole circuit. As the resistance through the pencil increases, more voltage is used there and the potential drop across the light bulb decreases. Less voltage means less power and less brightness.

Reinforcement Activities
The above demonstration is a good activity to do before talking about rheostats, or having the students use a Wheatstone Bridge apparatus.

Students should know about the effect of length on resistance in a conductor. Have students investigate this further using mounted resistance coils. Different lengths, gauges (thickness) and types of wire are given to students for them to investigate. Students can easily design their own experiments to test the effects of these three characteristics on the resistance of a wire.

Hot Air Balloons

bpearson — Wed, 27 Jan 2010 18:48:38 +0000

Materials

5 sheets of tissue paper per student or group
one glue stick per student
markers for decorating (optional)
dry fuel tablets
2′ tall stove pipe
3 hair dryers (alternate material to replace fuel tablets and stove pipe)
scissors

Procedure

Have students pick out five sheets of tissue paper and a glue stick. It is best if students work in groups of two or three.
Have students lay the first sheet of tissue paper on a clean flat surface and apply a solid line of glue stick to one of the long edges of the tissue paper
Immediately have students place their next sheet of tissue paper on top of the line of glue so that the two sheets overlap about ¾”.
Continue this process until you have one large sheet made up of four sheets of tissue paper glued long side to long side as shown in the diagram below.
Then glue the short end of the fifth sheet to the top of first sheet, short side to short side as shown in the diagram below.
Glue edge one to edge two with about ¾” overlap so that the tissue paper forms a box shape that is open on both ends.
Cover the top edge of the box with the fifth sheet of the tissue paper, gluing heavily around the edge and covering over top of the box to form a seal with no leaks. The bottom of the hot air balloon should remain open.
Have student decorate their balloon if they wish, being careful not to rip the balloon. Even the smallest hole may cause the balloon not to fly.
Take the balloons outside and have the students hold the bottom edge of the balloon over the heat source. Have student be careful not to touch the heat source, or allow the tissue paper to touch the heat source as the tissue paper might catch on fire. Be ready to extinguish any fires by having water and an extinguisher ready.
After the inside of the balloon has heated up, have the students count down from three and all let go of the balloon. On a good day the balloons with fly three stories high before losing their air and coming back down.

SAFETY PRECAUTIONS
Make sure that students do not run after the balloon, especially younger children will be looking up and not in front of them and my trip or bash into other students doing the same.

Make sure that students do not try to have the balloons land over their heads, even when the balloon is falling, the air inside the balloon can be very warm

Explanation
As the air inside the balloon is replaced by the hotter air from the fuel tablet or hair dryer, the density of air inside the balloon becomes less dense then the air outside the balloon. Since warm air rises, the air attempts to rise, thus pushing the balloon upward until the air inside the balloon cools down.

This can also be looked at in terms of buoyancy. The buoyant force needs to be greater than the gravitational force of the balloon in order for the balloon to rise. The density of the balloon changes when the air in the balloon heats up. When the weight of air that the balloon displaces is equal in weight to the amount of gravitational force on the balloon and the air inside the balloon, the balloon will begin to float.

Reinforcement Activities
It is often difficult to get the balloons to launch correctly and it takes up class time to have the students build the balloons. There is a simpler, easier, more durable way to perform this experiment, by buying the pre-made kit listed below.

A similar and quite amazing activity is the Giant Solar Bag. This 50 foot bag when filled with air will magically rise off the ground if placed in a direct sunlight and allowed to heat up. This is a very impressive and inexpensive demonstration that illustrates the same concepts above.

Book & Paper: A Discrepant Event

bpearson — Mon, 25 Jan 2010 18:17:31 +0000

Materials

Textbook or Notebook (one per student)
Piece of paper cut to fit a size smaller than the surface area of the book or notebook

Procedure

Lead students through a series of four mini-experiments. Have students make a hypothesis as to what will happen before each experiment and have the students explain to each other why they think the way they do. It is very important for students to explain their thinking and debate about it in order to correct it.

Experiment 1: Have the students hold the book and the piece of paper side by side and simultaneously drop the book and the piece of paper as shown in the diagram below.
Ask the students, which will fall at a faster rate, the book or the paper? Have them write a hypothesis, share their ideas, and then try the experiment. Ask them why they think the book fell faster. Most of them will say that the book is heavier and heavier things fall faster, which is incorrect, but do not correct their thinking just yet.
Experiment 2: Now tell the student they are going to put the piece of paper underneath the book and have the students answer the question which will fall at a faster rate, the book or the paper? Again, have them write down, explain, and share their ideas before they try the experiment. Many will think that the paper, being lighter, will fly up from underneath the book fall at a slower rate. This is incorrect, but do not correct them.
Have the students try their experiment and then explain their results. The paper will stay under the book. Many students will still hold on to the miss conception that the paper must fall slower because it has less mass and will explain the phenomenon by saying that the book pushed the piece of paper down. This is incorrect. At this point you will have some students that are starting to get the idea and will argue that mass does not affect the rate at which something falls to the ground. Let the students intellectually debate this.
Experiment 3: Have the students place the piece of paper on top of the book and again have the students predict which will fall at a faster rate, the book or the paper. Set up experiment as shown in the diagram below.
The paper will fall at the same rate as the book and appear to stick to the top of the book. Some students will explain this as some sort of suction, in fact students might believe there is something sticky on the top of the book. Have them check to make sure there isn’t anything sticky.
Experiment 4: Have the students drop the book and the piece of paper again side by side, this time crumple up the paper into a very tight ball. Be sure to discuss that the mass of the paper does not change by crumpling it up, it still has the same “heaviness”. Again let the student predict what will happen by answering the question which will fall at a faster rate, the book or the paper. Have the students explain their reasoning.
The book and the piece of paper will both hit the ground at the same time this time. Have the students debate why the book and paper fall at the same time.

Discussion questions

What has more mass, the book or the paper?
Does the mass effect the rate at which something falls? Use the information you collected from the demonstrations to back up your answer. Be sure to write in complete sentences.
What is air resistance?
Does air resistance affect the rate at which things fall? Us the information you collected from the demonstrations to back up your answer. Be sure to write in complete sentences.

Explanation
Mass does not effect the rate at which something falls to the ground. Assuming no air resistance, all objects accelerate towards the ground at a rate of 9.8 m/s2. The reason the paper fell slower the first time is because air resistance was pushing up on the paper resisting its motion. Since the paper has less gravitational force acting on it than the book, the upward air friction force effects the acceleration due to gravity the greatest, causing the paper to accelerate slower than the book.

In the second and third experiments, the air resistance of the paper is blocked by the book. The piece of paper on or under the book acts the same as all the pieces of paper inside the book. They fall at the same rate and act as one object.

In the last experiment, the paper is crumpled into a tight ball. Decreasing the surface area of the paper will decrease the air resistance and the paper is now allowed to fall at nearly the same rate as the book.

Reinforcement Activities
Have students accurately measure the acceleration due to gravity using photogates, spark timers, or electric timers for greater accuracy. A list of products available to do just this is provided below.

For students who need more reinforcement of the above activity have the students play with the Galileo’s Experiment Apparatus. This apparatus simultaneously releases two different massed balls and show that they both hit the ground at the same time. Quick and easy to use, this device also allows students to explore size and density variations in fall objects as well.

Eliminate the effect of air resistance all together by dropping a penny and a feather in a vacuum tube. Also an excellent conceptual knowledge check to the above activity, have the students predict and explain what happens when two objects fall on earth without air resistance acting on them.

2″ x 4″ Electrostatic Magic

bpearson — Sat, 23 Jan 2010 15:42:58 +0000

Materials:

Old Golf tube, or some other large plastic tube
Wool sock or shirt, or something to rub the tube with so it will acquire a charge
4″ diameter watch glass
8′ long or so two-by-four

Procedure:

Place the watch glass on a table upside down so that the lip of the watch glass is flat on the table
Balance the 2″ x 4″ on the inverted watch glass so that no part of the 2″ x 4″
Rub the golf tube several times with the wool so that the tube acquires a negative charge
Place the tube near, but not touching one end of the 2″ x 4″ and wait for a few seconds
The tube will begin to attract the 2″ x 4″ continue to move the tube away from wood as the end of the wood follows, keeping the wood about a distance of 1″ to 2″ away from the end. If you want you can start the tube rotating in the other direction by placing the tube on the other side of the wood

Explanation:
The golf tube is negatively charged, and negatively charged objects can attract things that are both positive and neutral. Since the wood is neutral, the wood is attracted to the rod. The amount of friction that the 2″ x 4″ would normally experience is greatly reduced by allowing the 2″ x 4″ to pivot on the watch glass.

The reason neutral objects attract to uncharged objects is because all neutral objects are made up of an equal number of electrons and protons. The electrons surround the nucleus of the atom. As a negative object is brought near the atom, the electrons slightly shift their position around the outside of the atom to move away from the negative charge; therefore the end of the atoms closest to the negative charge is slightly positive. The positive charges are attracted to the negative tube and thus the wood is attracted to the tube.

Reinforcement Activities:
There are many fun electrostatic experiments that can be done. One of my personal favorites is using a Van de Graff Generator. The students are instantly engaged by something that can give off sparks. There are many fascinating demonstrations that can be done from making a student’s hair stand on end, to making cereal and metal pie tins fly around the room.

Investigate static electricity by using the tried and true tool of Benjamin Franklin, the electroscope. Have students create different charges and study their effects on the electroscope.

Create mini-lightening bolts in your classroom and learn about electric charge using a Wimshurst Static Machine. Sparks can be around four centimeters long!

Wine Glass Resonance & Singing Rod

bpearson — Thu, 21 Jan 2010 14:35:17 +0000

Learning standards covered by this activity:

Major Understanding

4.3f Resonance occurs when energy is transferred to a system at its natural frequency.
4.3m When waves of a similar nature meet, the resulting interference may be explained using the principle of superposition. Standing waves are a special case of interference.

Process Skill

4.3 iii. identify nodes and antinodes in standing waves
4.3 vi Predict the superposition of two waves interfering constructively and destructively (indicating nodes, antinodes, and standing waves)

The above learning standards were taken from the Core Curriculum Physical Setting/Physics, The University of the State of New York, The State Education Department.

Wine Glass Resonance Materials

wine glass, the thinner the rim of the glass the better
water
soap

Procedure

Wash your hands with soapy water for best effect.
Fill the glass part of the way with water
Dip the tip of your finger into the water then slowly and lightly rub the rim of the glass with your moist finger
After a few seconds the glass will start to sing
You can change the pitch of the note by adding or subtracting water

Singing Rod Materials

Rosin (from the music room)
Metal rod from your ring stands (or any other uniform metal rod will do)

Procedure

Crush a pea sized amount of rosin on a piece of paper until it is ground into power.
Cover the tips of your thumb, index and middle finger of your non-dominate hand with rosin as if you were going to use the rosin to make a finger print.
With your other hand grasp the metal rod with your thumb and index finger exactly in the middle of the rod.
Stroke one half of the rod with your rosin covered fingers. After four or five strokes a standing wave will build up as the other end of the rod begins to resonate.

Explanation
Every object has a natural frequency. If you drop a set of car keys it makes a recognizable sound, as does dropping a pin. The sound that it makes is the natural frequency of the keys and the pin. You can get the rim of the glass to vibrate at the natural frequency of the glass by rubbing the rim with your finger. Your fingertips cause the glass to vibrate at it’s natural frequency. If this happens over and over again a standing wave builds up and you can get a sound with a lot of volume.

If you cause an object to vibrate at its natural frequency by having another object near vibrating at the same frequency you can set up a standing wave in the first object. This process is called resonance. This is what is happening with the singing rod. Since you are holding the rod at its middle point, the natural frequency of both ends of the rod is the same. As you set up a standing wave with your hand on one end of the rod, there is a standing wave set up due to resonance on the other end of the rod. Be careful, you can get the rod to sing loud enough to be painful to some people’s ears.

Reinforcement Activities
Look on the internet for small video clips of the Tacoma Narrows Bridge Collapse or Galloping Gurdie. Both of these names reference a bridge that collapsed due to resonance. The wind blew across the bridge at the same frequency as the natural frequency of the bridge. The standing wave produced was a couple of meters high and eventually the bridge shook so violently it collapsed. A great video for getting your students thinking and talking about standing waves and resonance.

Myth Busters did an interesting video on resonance trying to shatter a wine glass with their voice. Other Myth Busters videos are available for purchase through Cenco Physics. (See the related products section below.)

Allow students to play with resonance on their own using the differential and sympathetic Tuning fork set. Have students set up a wave on one tuning fork and then match the same frequency with a second tuning fork. When the tuning forks are matched in natural frequency then second fork will ring without being struck.

Rescue the Dollar Bill (Fun with Inertia)

bpearson — Wed, 30 Sep 2009 14:05:55 +0000

Learning standards covered by this activity:

Major Understanding

5.1i According to Newton’s First Law, the inertia of an object is directly proportional to its mass. An object remains at rest or moves with constant velocity, unless acted upon by an unbalanced force.
5.1q According to Newton’s Third Law, forces occur in action/reaction pairs. When one object exerts a force on a second, the second exerts a force on the first that is equal in magnitude and opposite in direction.

The above learning standards were taken from the Core Curriculum Physical Setting/Physics, The University of the State of New York, The State Education Department.

Materials

Glass root beer bottles
Dollar bill or piece of paper cut into the size of a dollar bill

Procedure

Place a root beer bottle on the top of a table right side up.
Place a dollar bill on the lip of the bottle
Place another root beer bottle on top of the dollar bill upside down
Pull the dollar bill about 2 cm from the edge of the lips of the root beer bottles.
With your left hand push the dollar towards the neck of the two bottles so that the dollar bows down a little and gives the dollar bill a little slack. See diagram:
With your right hand karate chop the dollar bill
With a little practice you should be able to remove the dollar bill from between the two root beer bottles leaving the root beer bottles standing one on top of the other.

Explanation/Possible Discussion Questions

1. In the space provided below, draw a picture of the two root beer bottles and the dollar bill. Draw in and list all the action reaction pairs possible for this set up.

Answer:

The top bottle is pushing on the dollar bill, the dollar bill is pushing up on the top bottle.
The dollar bill is pushing down on the bottom bottle, the bottom bottle is pushing up on the dollar bill.
The bottom bottle is pushing down on the table, the table is pushing up on the bottle.

2. Try to pull the dollar bill out from between the two bottles. (Hint, pull quickly) The top bottle should stay put if you pull quick enough, explain why this happens in terms of Newton’s 1st Law.

Answer:
The top bottle is an object at rest, it tends to stay at rest unless another force acts on it. If you pull the bill with enough force, you over come the coefficient of friction and the bill and lip of the bottle separate.

Reinforcement Activities
The inertia ball shows students what an object at rest, stays at rest really means. Introduce inertia by showing two discrepant events and have students discuss possible explanations.

Have students experience a world without friction by riding on a hovercraft. They will soon learn through experience that it requires a force to start and stop an object. Help students understand Newton’s first law and distinguish between acceleration and velocity.