How Physics Applies at the BEACH

We always talk about how we can use physics in our daily lives, but how can we continue to recognize what we've learned this year throughout the summer? Here are 10 ways:

#1

Let's say you are lugging your a cart to the beach and in it is your beach ball.  When you hit a bump in the road, the ball is thrown into the air.  However, it doesn't fall out of the cart, but travels with it. Why is this?
Newton's law explains inertia, stating that an object in motion will stay at motion and an object at rest will stay at rest unless acted upon by an outside force.
As you pull the cart, the cart has a certain velocity.  Because the ball is contained in the cart, it is moving with the same velocity as the cart.  Since no force is stopping the ball, it will continue to move with the cart, therefore land back in the cart

#2

Let's say you and your friends decide to jump off the cliff at the beach
However, you don'y want to land on the rocks below.
You can use Physics to calculate where you will land:

Projectile throwing is much like free fall straight down, however, one must take the horizontal velocity into account as well as the vertical.  Finding horizontal velocity is easier because it stays constant (due to Newton's first law).

If given the distance (d) in the graph shown above, you can use the  (d = 1/2(10)t²) equation to solve for the time (t).  Once you know the time, you can use the (v=d/t) equation to find the distance, and make sure you won't land on the rocks!  

#3

As you go to the beach each day, you notice the the tide changing.  Here's how you can impress your friends by explaining why this happens: 

The Earth's natural tides can be explained through the pulls of gravity and Newton's 3rd Law.

Each day there are 4 tides in total:

• 2 high tides
• 2 low tides

You can explain these tides through Newton's 3rd Law.

Notice how, in the image below, the distance A is lesser than the distance B.

Because the distances are different, point A and point B will experience different forces from the moon's pull.

We know that Force and Distance are inversely proportional.

Therefore, 

• Since B has a greater distance, the force will be lesser,
• And since A has a lesser distance, the force will be greater.

This DIFFERENCE IN FORCE causes the water surrounding Earth to create an oval:

And depending on where you are located on the Earth's surface, you will experience a low tide or a high tide

#4

When you think you have these tides all figured out, you notice high tides are sometimes higher, and low tides are sometimes lower than usual.

You can explain this through physics too:

There is also a pull between the Earth and the Sun.  As the distance between the sun and Earth changes throughout the year, this pull has more or less effect.  (Less drastic than the moon however, but still noticeable)

This is why we have Spring and Neap Tides:

#5

You and your friends go to the carnival on the beach.  Jasmin decides to climb toward the ceter of the ferris wheel because she wants to go faster but you know this will not work.  Physics can explain why...

Jasmin and Princess will experience the same number of rotations, however, Princess will have to go faster (have a greater tangential speed) to reach them.  This is because her radial distance is greater.

v ~ r w

(tangential velocity ~ radial distance * rotational velocity)

Since Jasmin decreased her radial distance, she therefore decreased her tangential speed as well.  Therefore, she will go slower than us.

#6

You decide to pack some strawberries for a snack at the beach. So, you cut up strawberries to put in a ceramic bowl and put plastic wrap to cover them. This plastic wrap doesn’t just magically stick to the bowl. Thanks to physics we know why exactly, the plastic wrap sticks to the bowl. 

The plastic wrap is charged by friction and when brought near the bowl, the bowl polarizes. The positive charges in the bowl move close to the negative plastic wrap and the negative charges in the bowl move away from the plastic wrap. The distance between the opposite attractive chargers is smaller than the distance between the like repelling charges. Coulomb’s law states that the force between any two charges are inversely proportional to the distance. F=kq1q2/d^2. Because there is a greater distance between the repulsive forces, the forces between them will be less than closer attractive forces. Therefore, the plastic sticks to the ceramic bowl.

#7

You carry your fruit in a basket to the beach. Although this may feel challenging and it may feel like you are doing a lot of work, however, in physics terms, you are actually doing NO work. The force, which is the basket, being pulled down by gravity is not parallel to the horizontal distance the cooler is moving. Work is the effort exerted on something that will change its energy. 

         Work = Force * Distance
One important thing to remember is that in order to calculate work, the force and distanceMUST BE PARALLEL 

Therefore, you only do work when you lift the basket, but not in carrying it across the beach.

#8

While you're at the beach, a lightning storm rolls in.  Where did this lightning come from?  Physics can explain that...

The movement of particles in the clouds causes friction which causes the cloud to polarize. Because the electrons move to the bottom of the cloud, the positrons from the ground become attracted to the cloud, therefore polarizing the ground as well. The cloud and ground want to equalize, so once the pull builds to a certain point, an electric shock will transfer charge to equalize them, which we see as lightning

#9

It's so hot at the beach that you go home and stand in front of the fan.  You wonder how this fan spins.

  This is because inside the fan is a motor.  Motors convert electrical energy (from the wall socket) into mechanical energy that causes the fan blades to spin.  In a motor, a current runs through a coil, which feels a force because it is within a magnetic field. It feels this force because it is MOVING and all moving charges feel a force in a magnetic field. The force felt by the wire causes a torque, causing the coil to spin.  This spin produces usable mechanical energy.

#10

While you and your friends take a walk on the beach at night, you wonder why you've never seen the Northern Lights.  

Physics explains thy the Northern Lights only happen at the poles:

Cosmic rays released from outer space are directed toward the Earth's equator.  However, once the rays come into contact with Earth's magnetic fields, they spin and follow the fields all the way to the poles, where they create waves of light.  This is helpful to our health because cosmic rays can be very dangerous to our health, but sadly, we can't see the unless we travel to the poles.

YAY PHYSIX!!!?

Wind Turbine Blog

The Physics of a Wind Turbine
A wind Turbine is a generator.  This means it converts mechanical energy (wind) into electrical energy (voltage).  The wind turns the propellors which causes the magnets to turn with it.  As these magnets spin, they are surrounded by coils of wire.  Because the magnets are spinning, the magnetic fields are then changing, causing the electrons in the wire to move, creating a current.  This current is then run through the alligator clips, and measured as voltage.

Materials

• Paint Roller
• Cardboard
• Hot Glue
• Wood Glue
• Paint Stirrers
• 4 Magnets
• 2 Coils of Wire

Uses

Our entire propellor was made up of two things: a paint roller and cardboard.  We used a saw to cut the end off of a paint roller, and bent the bars out to create propeller arms.  We then added cardboard flaps to each arm to increase air resistance, creating our propellor

We attached 4 magnets around the center axel of this propellor using hot glue

We then created a small wooden frame out of paint stirrers and wood glue.  Within this frame, we placed our 2 wire coils on opposite sides.  We then brought the entire frame to the rotating magnets at the center of the propellor, creating a generator. 

Problems

One problem we encountered was in trying to hot glue the magnets to the propellor, they kept sticking together.  Also, we worried that the heat and the force from these collisions would weaken our magnets.

We also found difficulty in making sure our frame and coils had a stable base, which we ended up solving by simply holding it up to the propellor, creating a mobile generator. 

Results

Our group was me, Maiya and Princess.  As a Result, our group ended up generating .3 volts. This had less to do with the speed of our turbine, which went pretty fast, but rather the stability of our wire coils.  If we were to make this a more successful generator, we would need to stabilize the coils around the magnets.

Our Turbine

Motor Blog

(from Jasmin's Blog)

Here is a picture of our battery powered motor. 
To make this motor, we used the following materials:

• Wooden block
• Batery
• Magnet
• Coiled Wire
• Paper clips
• Rubber band
• Electrical Tape

The battery supplies voltage and current
The coiled wire provides a pathway for current to flow.   The more turns in the wire, the greater the force is felt
The paper clips connects wire to battery, completes the circuit
The magnet creates a magnetic field, causing the moving electrons in the flowing current of the wire to move

Armature
In order to allow our motor to function correctly, we had to scrape off one side of the coil. We only scraped off one side because if we scraped all around, current would want to flow in both directions. We then attached the wire to the paper clip to allow the flow of current.

Why does the motor turn? 
The magnetic field is the reason the motor is able to function. The force of the magnet is charged by the battery which is perpendicular to the motor. This creates force. The magnet causes a magnetic field, therefore charges move in one direction, causing the motor to rotate. It is able to turn because the force is in one direction. Again, we scraped off the sides of one end of the coil, because if force was going in both directions, the motor would not be able to function. 

UNIT 7 REVIEW

In this Unit, we covered these major points:

1. Magnetic Fields and Poles
2. Magnetic Domains
3. Electric Currents with Magnetism
4. Motors and Generators
5. Transformers

Magnetic Fields and Poles

Magnetism is the force due to the movement of charged particles.

Regions called magnetic poles give rise to these magnetic forces.  

Magnetic fields are caused by MOVING charges. 

The direction of magnetic fields in a permanent magnet are released from the North side and enter through the south side:

  
We can use magnetic field lines to show why like poles repel and opposite poles attract like this:

As shown in the image above, the like poles' magnetic field lines are going toward each other, causing them to bounce off and repel.  However with the opposite poles, the lines are both going in the same direction, and they act together.

The Earth has magnetic poles as well as geographic poles.  This can be confusing because the geographically north end of Earth is actually it's magnetic south pole

A compass works because of Earth's magnetic poles. A compass needle is really just a magnet that is free to spin. The South pole of the compass needle is attracted to the North pole of the earth, which is the geographical South Pole. The North end of the needle is attracted to the south pole of the Earth which is geographically the North Pole. 

What causes the Northern Lights?

Cosmic rays released from outer space are directed toward the Earth's equator.  However, once the rays come into contact with Earth's magnetic fields, they spin and follow the fields all the way to the poles, where they create waves of light.

Magnetic Domains

Magnetic Domains are clustered of aligned atoms.

For instance, all Iron has magnetic domains.  However, not all Iron is magnetic.  This is because the domains may not be aligned. A domain is a group of atoms whose electrons are spinning in the same direction.

A ferromagnetic material is one that is highly susceptible to magnetism, such as a paper clip or a nail.

This is how we can magnetize a ferromagnetic paper clip:

If the paper clip is jostled, the domains will come out of alignment.

A Permanent Magnet can be weakened when it's domains are unaligned as well.  This can happen when the magnet is dropped or heated.

Electric Currents and Magnetism

Magnetic Force on Current-Carrying Wires

When a wire is carrying a current, it has a magnetic field around it.  Use the "right hand rule" to find the direction of that magnetic field:

An electromagnet is a current carrying coil of wire. 

The strength of an electromagnet is increased by the number of turns in the coil.  This also increases the voltage of the wire, increasing the current, therefore strengthening the magnet.

If the magnetic field is continuously changing, this is how a generator works. 

Motors and Generators

Motors and generators have almost identical construction but opposite roles. Motors turn electrical energy into mechanical energy, whereas generators turn mechanical energy into electrical energy. In a motor or generator, a current runs through a coil, which feels a force because it is within a magnetic field. It feels this force because it is MOVING and all moving charges feel a force in a magnetic field. The force felt by the wire causes a torque, causing the coil to spin.  This spin produces usable mechanical energy.

DC (direct current) cannot be used for a transformer because the current it produces only moves in one direction whereas the AC (alternating current) continuously changes the direction of the current, which causes the change in the magnetic field. If a DC current were used, the generator would only work briefly when turned on ant turn off, where as an AC current constantly goes back and forth. 

Transformers

Transformers are used to increase or decrease voltage through electromagnetic induction  The small box connected to your computer charger is actually a transformer. 

A transformer is simply made with two coils of wire. There is a primary coil and a secondary coil. The primary coil is connected to the power source so it is the input and the secondary coil is the output.  Whenever the primary switch is opened or closed, voltage is induced to the secondary switch.

The number of turns in the wire is directly proportional to the voltage induced. The more turns in the wire, the more voltage there will be. The less turns the less voltage there will be. If the secondary has more turns than the primary, it is a step up because the secondary will produce more voltage than the primary. If the secondary has less turns than the primary it will be a step down because the secondary produces less voltage than the primary.

This equation shows the relationship between primary and secondary coils:

# of Primary Turns/Primary Voltage

 =

 # of Secondary Turns/Secondary Voltage

the powers are equal:

Power Primary = Power Secondary

because Power = Current * Voltage,

IV primary = IV secondary

This unit, the section I had the most difficulty with was generators.  I didn't understand why the coil moved. I finally understood it when i realized current is a moving charge and moving charges feel a force in a magnetic field.  Besides that, induction was a little complicated.

UNIT 6 REVIEW

In this Unit, we learned 6 major topics:

1. Charges and Polarization (Coulomb's Law)
2. Electric Fields and Electronic Shielding
3. Current
4. Electric Potential/Electric Potential difference
5. Capacitors
6. Ohm’s law and Resistance
7. Power
8. Parallel and Series Circuits

Charges and Polarization

When there are more electrons, like the second image above, the object is negatively charged

Whe there are more protons like the third image above, it is positively charged

Like charges attract each other

And opposite charges repel each other

How do these charges travel and move? There are 3 ways:

1. Direct contact (shocked someone by touching them)
2. Friction (steal electrons from eachother)
3. Induction charge without contact (lightning) shown below

Why does our hair stand up after putting on a sweater?

• Sweater steals electrons through friction, therefore becoming negatively charged
• Therefore, each hair is becoming positively charged
• The now positively charged hairs will repel because they are like charges, therefore will stick up

Polarization

When an object is polarized, it is not charged, the charges are simply rearranged
Therefore, the net charge is still 0

Conductor vs Insulator:

• Conductors let charges move through them
• Insulators stop charges from moving

Conductors can become polar

Polarization is when charges in an object separate from each other

In the image above, the ball is now polarized because a negatively charged pole separated the charges to either side

We can see polarization in LIGHTNING

The movement of particles in the clouds causes friction which causes the cloud to polarize. Because the electrons move to the bottom of the cloud, the positrons from the ground become attracted to the cloud, therefore polarizing the ground as well. The cloud and ground want to equalize, so once the pull builds to a certain point, an electric shock will transfer charge to equalize them, which we see as lightning

How do lightning rods protect structures?
Lightning rods conduct the positive charge on the ground's surface and bring it to a high point to reach further into the air. If lightning strikes, it will take the path of least resistance to the ground. The lightning rod provides much less resistance than a wooden structure.

Coulomb's Law states that force between any 2 charges is inversely proportional to the distance

F= (k q1 q2)/d ²

where q stands for charge

For the question why does saran wrap stick to metal more than plastic....

As you can see above, the saran wrap (in the purple) has a negative charge (because as it was unrolled, friction caused it to steal electrons)
When you bring the negative wrap to the bowl, the positive charges will go toward the wrap and the negative charges will go away from it.
The bowl is still neutral, however, it is now polar.
The glass bowl will remain polarized.
However, metal in a conductor. So once the wrap comes close to the metal bowl, the negative charges will travel straight to the ground
But why does it stick? Coulomb's Law!
The distance between the attractive force is small, so it will have a large force
The distance between the negatives is much larger, therefore will have a much smaller force
Therefore, the attractive force will be greater, causing the plastic wrap to stick

Electric Fields
Electric fields are the area around the charge that can influence (push or pull) another charge.
How do we draw electric fields?

For the proton, arrows face outward, and for the electron, arrows face inward

• If a positive charge were close to the positive charge on the left, it would repel away
• If a positive charge were close to the negative charge on the right, it would be attracted inward

And notice how as you travel further from the charge, the lines get farther apart. This indicates the strength of the push/pull decreasing

Electronic Shielding
How can we keep things like microchips in computers safe from outside charges?
Electric Shielding!

When surrounded by a conductor, for example, metal box. Positive charges will accumulate all over the box. Because of electric fielding, the sensitive equipment inside will not feel a force. This is because since the metal's charges are all evenly distributed, force will remain the same AT ALL points within the container.

Current

Current is the flow of charge

Charge flows when there is a difference of potential energy between two points, and it will continue as long as there is electric difference between these two points.

It is important to remember that voltage causes current, current does not cause voltage

Current comes in two forms, AC and DC (not the 70's hard rock band)

• AC - Alternating Current  
• switches direction
• used in batteries
• DC - Direct Current
• used in wall sockets

How do batteries work and why do they eventually stop working?

Batteries are able to have current because they have a difference in electric potential or a voltage between the positive and the negative side. Overtime, the difference decreases and eventually there is no longer an electric potential difference. When there is not an electric potential difference, there is no current, which is why batteries stop working.

Why do flashlights get dimmer?

Because as stated above, as a battery wears out, it's voltage decreases.  We know that voltage causes current, so as voltage decreases, current decreases as well.

Electric Potential
A charged object has electric potential through it's location in an electric field.

Electric Potential Difference is the difference in

∆PE = ∆KE

Electric Potential = PE / q

Voltage= ∆PE / q

However, as an electron gains potential energy, it does not get kinetic energy.  Instead, it goves it our to the circuit as power.

Capacitors

In order for a camera to produce a flash, a large amount of energy is needed. This energy cannot be created in such a short period f time. Therefore, it requires a capacitor. Capacitors build up energy over a period of time and release it all in a short burst.

Speed of electrons - are electrons as fast as the speed of light?

No - Electrons moving through a conductor are moving very slow. However, they move all together like a train, so when one moves even slightly, every other electron in the conductor will move almost immediately

Ohm's Law
The amount of current that exists depends on the voltage as well as the electrical resistance.
This brings us to Ohm's Law stating that...

V = I * R

The electric potential difference between two points on a circuit (V) is equal to the product of the current between those two points (I) and the total resistance of all electrical devices present between those two points (R). 

Resistance is affected by heat and thickness of the wire.
Therefore the resistance of a wire depends on the thickness, length and material.

• Heat increases resistance
• Width (of the wire) decreases resistance

Why do lightbulbs burn out when you first turn them on?
When a lightbulb has been off, the filament has cooled.  Therefore, it has little resistance.  When a large current travels though, since there is little resistance, the filament will blow.
Electric Power
Power is voltage times current 

P = VI

And power's relationship with energy is...

Power = Energy/ Time

Series and Parallel Circuits
A circuit is a path along which electrons can flow
There are two different kinds of circuits, series and parallel
These circuits have a box supplying 12 V of voltage

Series

• voltages add
• current decreases?
• brightness decreases
• resistance adds
• when one lightbulb is removed, the whole circuit is opened, therefore stops working

Parallel

• voltages are the same
• current adds
• brightness remains constant
• resistance decreases by half

Houses use parallel circuits so you can use some outlets without having to use them all.  However, because current increases with each device added on, it can reach dangerous levels.  This is why we use fuses.

A fuse is connected to the circuit where it is still in series (before it breaks off into separate sections).  If the current reaches a certain point that is too great, the fuse will melt, therefore breaking the circuit, and cutting al devices off from the voltage source.

OVERVIEW - Units
Charge - q (Coulomb)
Voltage - V or J/c (volt or joules per charge)
Current (I) - A
Power - W (watts)
Resistance - Ω (ohm)