Top Ten Physics Examples in Sports

1.) Lets say you are skateboarding around your neighborhood. When you stop to take a rest your friend comes up to you and pushes your skateboard. To your surprise you fall exactly where you were previously standing on your skateboard while your skateboard rolls about 20 feet away. The reason why this occurs is because of Newtons first law which states that an object in motion stays in motion and an object at rest stays at rest unless acted upon my an outside force. Because you were initially at rest your body tends to stay at rest even after your friend pushes your skateboard.

2.) In professional skydiving, divers have to take into consideration their acceleration, speed, and air resistance. The skydivers acceleration is at its greatest when they first jump out of the plane (acceleration = net force/mass). As the person falls their force of air resistance increases. The equation used to solve for the divers net force is F weight minus F air. As F air increases F net decreases, and once the F net reaches zero the diver is in a state called terminal velocity, meaning that they are moving at constant velocity.

3.) In baseball say a ball was hit at a 45 degree angle and is moving 20m/s in the horizontal direction and 40m/s in the vertical direction. If you wanted to calculate how far away the ball will land you would use the physics equation distance = velocity x time (d=vt). Since we know the speed in the vertical direction we can calculate how long the ball will be in the air. 

Now that we know the ball will be in the air for 8 seconds we can plug it into the equation d=vt (note that the velocity used in this equation will be the horizontal velocity no the vertical). 

d = (20)(8), the ball will travel 160 meters.

4.) Lets say you are in a sail boat race, and you are trying to get to the other side of the river as fast as possible so that you can beat your opponent. The fastest way to travel across the river would be to paddle in the diagonal direction up stream so that your boat moves straight across. The reason why this works is because of vectors which show direction and magnitude. Here is an image I made for clarification.

5.) Surfers who like to practice when the waves are the biggest need to take into account how high and low tides work. Physics is used when figuring out when hight and low tide is, for it has to do with the force from the moon and they are also caused from the difference in force from either side of the earth. In this image both sides A and B are experiencing the same force and are both in high tide due to the positioning of the earth.

There are two types of tides, and they are spring tides and neap tides. Here is what they look like:

Highest of high tides and lowest of low tides occur when there is a full or new moon (Spring tides). Ideally the best time to go surfing is when there it is high tide. Each day there are 2 high tides and 2 low tides meaning that every 6 hours they alternate.

6.) Why do wrestlers keep their legs shoulder width vs. feet together? There is physics in why they does so, because when a wrestler opens up their stance they are widening their base of support. The wider their base is the more support they have making it harder for someone to push them over. Pretending that the rectangles are humans, you can easily see that the first person is more likely to fall over because they have a smaller base of support.

7.) When performing the triple dive in professional diving, there is physics behind why divers extend their arms and legs after spinning. When a diver opens up their arms and legs their rotational velocity decreases, because they are putting more mass away from their rotational axis. This gives the diver more rotational inertia. By doing this they stop their spinning motion allowing themselves to dive into the pool with minimal splash.

8.) In race car driving, members need to take into account the physics concept of centripetal force which means center seeking force. When the race car rounds a corner at top speed the friction between the tires and the road provides a centripetal force that keeps the car on the road. The person who is in the car will feel a force towards the center of the curvature, and the name for it is centripetal force.

9.) Physics can be seen in gymnastics, for it explains why it is safer for gymnasts to practice on soft surfaces rather than on the concrete.  The reason why is because no matter what they land on they are going from moving to not moving, therefore the change in momentum is the same regardless of how they are stopped 

p=mv

∆p = p final - p initial

Because the change in momentum is the same regardless of how the person is stopped, the impulse is also the same regardless of how quickly you are stopped.

∆p = J

J= F x ∆t

It would be foolish of the gymnists to practice on concrete because since the impulse is the same the force they will experience when they land will be greater and the change in time will be smaller. While if the gymnast practices on softer surface their force will be smaller because the softer surface increases their stopping time. And less force means less injury.

10.) Physics can be seen while biking, for the concept of torque is applied to the bike pedals which cause it to move. The metal shaft that lies perpendicular to direction in which you push down on the pedal is the lever arm (torque =  force x lever arm). Force and lever arm are inversely proportional meaning if you increase the pedals lever arm you use less force and vis versa. The biker can use torque to measure how much force is acting on the pedal causing it to rotate.

Wind Turnbine

Background:
The primary physics concepts involving wind turbines is the use of a generator. The generator runs due to the interaction between the coil of wire and the magnets.  The mechanical energy is the input and electrical energy is the output. Another primary concept is that in order for voltage to be induced the magnetic field needs to be changing. To create this change, we hot glued four magnets around a short wooden cylinder with alternating north and south poles. The purpose of the north and south poles is so that when the propellers spin the magnetic field around the coils would alternate thus inducing voltage.
Here are some images of my groups wind turbine.

Materials and Methods:
The materials needed to reproduce our design would be pipes, thin wire (to make coils), hot glue, 4 small magnets, short wooden cylinder, one long pipe and one short 90 degree pipe. The long pipe was the shaft that held up our wind turbine and the 90 degree pipe connected to the tope was were we placed our generator. For the Generator we attached 4 small magnets around a short wooden cylinder, and made two coils of wire that were placed on the north and south side of the generator. We left about two inches of wire outside of the coil so that we could attach the alligator clips to calculate the turbines voltage. The propellers were made out of cardboard and were attached to the generator by wooden sticks.

Here is an image of what our pipes looked like.

                

Results and Discussion:
What I learned form this assignment is that the more coils of wire and loops you have, more voltage will be induced. This idea goes back to the physics concept of primary and secondary sources. Although work is equal in the primary and secondary sources, more voltage can still be induced when there is more loops of coils. What was most difficult for us while constructing our turbine was attaching the magnets to the wooden cylinder, for the magnets were hard to pull apart. My advice to future physics students doing this project is to stick with 2 coils of wire, making 4 was difficult to do, and we would of spared a lot of time if we didn't spend it trying to figure out the 4 coils.

Here is a video of our wind Turbine working (creds to Mo Carlton for finishing the project)

Magnetism Unit Blog Post

In this unit I learned about:

1. Magnetism; magnetic poles; electromagnetism
2. Forces on charged particles in an electric field; Motors
3. Electromagnetic induction and common applications
4. Generators and energy production
5. Transformers and energy transfer from power company to home

Magnetism; Magnetic poles; electromagnetism;
Magnetism refers to the force between magnets. Objects that produce magnetic fields will have poles that will attract or repel other magnets (like poles repel and opposites attract). The source of all magnetism is moving charges.

Like poles repel because the magnetic field lines are in opposite directions which causes them to repel. The magnetic field lines show the direction of the field at different points.

The field lines between the two like poles diverge.

Opposite poles attract because their field lines line up in the same direction. Note how the field lines enter in from the south pole and out through the north pole

One of the major questions we were asked about magnetism was; Explain and who how you turn a paper clip into a magnet?

The Answer is because the cluster of atoms in a paper clip have electrons that are spinning in the same directions, this is referred to as the magnetic domain. But the domains are pointing in deferent directions at different times. Below is an image showing what the domains look like between a unmagnetized object and a strong magnet.

When the paper clip is placed in proximity to the magnet, the domains within the paper clip align with the magnet thus making it a magnet with a north and a south pole. The paper clip is now attracted to the magnet because they are in the same magnetic field, due to the fact that opposite poles attract.

Forces on charged particles in an electric field:

The rule that we learned with this topic is called the right hand rule. When a charges is placed in a magnetic field that charge feels a magnetic force. The charge moves relative to the magnetic field, and the charges velocity is perpendicular to the direction of the magnetic field. This causes the particle to spiral around the magnetic field. Here is an image showing you how it works.

The thumb represents the force and your other fingers represent the magnetic field which is drawn withe the vectors.
Another main question regarding the force on charged particles in an electric field is what causes the northern lights?
Like magnets the earth also has a north and south pole, but what we know geographically to be the north pole is actually the magnetic south pole and the geographical south pole is actually the magnetic north pole. Here is an image of the geographical poles and the magnetic poles of earth.

Therefore since the magnetic field deflects cosmic rays from traveling through to earth they instead spiral around the magnetic field and enter in the south magnetic pole. This is why there is more cosmic radiation in the north than in the equator. The spiral motion can be seen in this image.

Electromagnetic induction: is the phenomenon of inducing voltage by changing the magnetic field in loops of wire. Voltage is induced in a wire when either the magnetic field moves past the wire or the wire moves through the magnetic field. This concept can by understood through Faraday's Law which states: The induced voltage in a coil is proportional to the product of the its number of loops (more loops means more voltage), the cross-sectional area of each loop, and the rate at which the magnetic field changes within those loops. Because more loops mean more voltage it takes more work to induce it. For example pushing a magnet into a coil with many loops is difficult because the magnetic field of each loop resists the motion of the magnet.

Generators and energy production:

A generator is when voltage is induced by moving a coil than by moving a magnet. The arrangement of rotating coil in a stationary magnetic field is called a generator. A motor and a generator are basically the same thing, for the only thing they differ in is the roles of their input and output are reversed. In a motor electric energy is the input and mechanical energy is the output. While in a generator mechanical energy is the input and electric energy is the output. But both of the devices transform energy from one form to another. Because the voltage induced by the generator alternates, the current produced is ac.

Transformers and energy transfer from power company to your home:
A transformer is a device used to reduce (step down) or increase (step up) voltage of an alternating current. In a transformer there is a primary and secondary source. The primary source is connected to the power source and only induces voltage in the secondary source when the magnetic field is changing through the coil. If the secondary coil has more turns than the primary source, the alternating voltage produced in the secondary coil will be greater than the voltage in the primary (step up).

Transformers are used by power companies to slow down the current. Companies want the current in the power line to be low because then energy doesn't go to waste in the form of heat. When current is high the wire heats up, but by increasing the voltage the current decreases. This is possible because power in the primary is equal to the power in the secondary.

Power (primary) = Power (Secondary)

VI = VI

As voltage increases current decreases and vis-versa.

One of the main questions asked was how do credit cards work?

The answer is that a credit card has a magnetic strip that has sectors that are magnetized in different ways following a code. The reader has a lot of different coils that are induced with voltage when put through the swiper. The computer interprets the electric signals back to codes.

What I have found difficult about what I have studied in this unit was the equations problems.

If a machine requires 10A current, what will the current drawn from the wall socket be? (Wall socket provides 120V)

Power (primary) = Power (secondary)

(120v)(I) = (

What made the lightbulb click was getting the problem wrong on the quiz, because being able to compare my mistake to the correct answers made me understand the problem more clearly. My persistence in class is pretty consistent. I work to turn in every homework assignment on time and when I don't understand a certain topic I make a conscious effort to come in during conference period to ask question. I have no goals for the next unit because this is our last physics unit of the year. A connection that I made between what we studied and everyday life was how a credit card reader is able to receive money from my credit card. 

Motor blog

The Battery: Supplies voltage to produce a current.
The Coil of Wire: Provides a pathway and allow the current to flow.
Paperclip: Connects the wire to the battery, and completes the circuit.
The Magnet: Makes magnetic field that puts magnetic force on the motor loop which makes it turn.

The current flowed from the battering up the paper clip and through the wire and motor loop and back down the other paper clip. The paper clips were attached to each side of the battery, thus completing the circuit (connected positive and negative sides).  The magnet located on top of the battery, created a magnetic field that put a magnetic force on the motor loop causing it to turn. The reason why we scraped the armature on one side was because we wanted current to flow while the loop was turning in one directing, for it prevented the current from flowing in both directions. The motor turns because of the magnet placed on top of the battery, creates a magnetic field. The vertical part of the loop felt the force of the magnet in opposite directions which created a torque on both ends of the wire this caused the wire to rotate. To apply the right hand rule the magnetic field (middle finger) would be in the upward direction and the force of the wire (thumb) would be towards the viewer. Since the sides of the wire are in opposite directions, the wire rotates. Once this half turn is complete the field of the electromagnet flips. The flip then causes the electromagnet to complete another half turn. The motor that we built is to small to be used to power an object. However it can be used for educational purposes and aid in further understanding in the the right hand rule.

Unfortunately there were some technical issues with my motor, meaning that I was not able to record it working. Here is a video of one of my classmates motor working. Enjoy!




Check out Cori's blog at http://coriphysics13.blogspot.com/

Charges and Electricity Unit Reflection

In this unit I learned about:

• Charges and Polarization (Coulomb's Law)
• Electric Fields
• Electric Potential/Electric Potential difference, Capacitors
• Ohm's Law and electric potential difference 
• Types of Current, source of electrons, Power
• Parallel and Series Circuits

Charges and Polarization: 

The three ways we learned how to make something neutral or to have a charge is by:

1. Direct contact
2. Friction (When objects rub against each other)
3. Induction: Way to charge without contact by bringing a charged object next to a negative object.

One of the big questions related to this topic was, why does hair stand up after putting on a sweater? The answer to this question is that when the sweater rubs against your hair it steals electrons from it (friction) moreover, the sweater becomes negatively charged, leaving your hair to be positively charged.   The hair stands up due to it's attraction to the sweater (positive and negative charges attract). 

Polarization: When an object becomes polar charges separate to opposite sides of an object (object is still neutral)

Coulomb's Law: States that the force between 2 charges is inversely proportional to the distance (the greater the distance the weaker force)

Electric Fields: 

Electric fields refers to the space around around every electrically charged body. Electric fields have both magnitude (force per unit of charge) and direction. The equation used for calculating the force a body is experiencing in space is E = F/q. The electric field is depicted with vector arrows which show the direction positive charges move.
An important thing to note about electric fields which make them different from gravitational fields is they electric fields can be shielded by various materials. For example charges inside a metal box stay is the same position because there is no force pulling them in one direction. The balance of positive charges around the box keeps everything in place (net force inside the box is zero).

Electric Potential, Electric Potential Difference, and Capacitors
 Electric potential energy is the energy a particle possesses by virtue of its location. If one was to push a charged particle against the electric fields then the work changes the electric potential energy of the charged particle.  If this particle was to be released then its potential energy changes into kinetic energy. When considering charged particles it is easier to consider the electric potential energy per unit of charge (per coulomb) A object with 12 coulombs of charge as a specific location has 12 times as much potential energy than a object with 1 coulomb of charge. But 12 times as much electric potential energy for 12 times as much charges is the same as 1 electric potential energy per 1 coulomb of charge.

The unit of measurement for electric potential is volt, therefore another name for electric potential is voltage.

Electric energy is stored in a device called a capacitor.

What is a capacitor?

A capacitor is a pair of conducting plates separated by a small distance; the plates are connected to a charging device such as a battery. The capacitor plates have equal and opposite charges when electrons are pumped through the battery onto the opposite plate. The charging of the plates in done when the potential difference between the plates equals the potential difference between the battery terminals.

In electric potential difference, charge flows from one end to the other.

Ohm’s Law and electric potential difference

Ohm’s law shows the relationship among voltage, current, and resistance.

Electric current is the flow of electric charge. Electric resistance depends on the thickness and length of the wire, for thinner and longer wires will offer more resistance. Electrical resistance is measured in ohms Ω

A big question involving current and voltage is; why does a flashlight get dimmer as the battery becomes weaker?

Answer: As a battery becomes weaker its voltage decreases, and with less voltage there is less energy per electron meaning that the current is stronger.

An example problem involving Ohms law is; calculate the current in the 480 ohms filament of a light bulb connected to a 120 V line.

Current = 120/480

Current = ¼ Amps

Types of currents, sources of electrons, and power

The two types of currents we learned about in class were direct and alternating currents

In direct current, charges flow in one direction. In alternating current electrons in the circuit are first moved in one direction then in the opposite direction.

Although most people may not acknowledge it, but when one flips the light switch on a wall they are completing the circuit thus allowing electrons to flow through the current (current is established at the speed of light note this is not the speed of electrons.  

Two common misconceptions about electric energy is one: electrons move through the wires by electrons bumping into one another like dominos. This isn't true because throughout the entire closed circuit all electrons react simultaneously to the electric field. The second misconception about electric energy is the source of electrons. The source of electrons come from the conducting circuit material itself, they are not something you buy or something you get from electrical outlets. 

Electric Power is the rate at which electric energy is converted into another form, such as mechanical energy, heat, or light.

Electric power =  current x voltage       -------->   P = IV

Watts = Amperes x volts

The relationship between power and energy: Power = energy per unit of time

Energy = power x time

Parallel and Series Circuits 

Series circuits: Wires are connected end-to-end forming a single path for electrons to flow. The total resistance to the current in the circuit is the sum of the individual resistances along the circuit path. The current is numerically equal tot he voltage supplied by the source divided by the total resistance of the circuit.

Here is what a series circuit looks like

Parallel circuits: Are connected to the same two points in the circuit, but the circuit branches of into separate pathways from point A to B as shown in the diagram. Because each device connects at the same two points the voltage is therefore the same across each device. As more branches are added current increases while resistance decreases.

Whenever overloading occurs in a circuit, there is more current than the wire can handle causing it to heat up and melt. To prevent the wire from melting and possibly causing a fire, fuses are used to connect the entire line that will melt if the wire gets too hot. When the fuse melts the circuit is disconnected thus sparing the wire. 

What I found most difficult about what I have studies is answering the question; Why do light bulbs often blow when they are first turned on rather than after they have been on for several minutes?

The answer to this question is, because when the bulb is turned off the filament becomes cold. But once you turn it on the filament heats up pretty fast due to the current that has just begun to flow. Often the filaments aren't able to handle the increased amount of energy flowing through them causing them to burn out. But when light bulbs have been on for several minutes they have already equalized and the electrons are flowing at a constant pace.

I overcame this difficulty by doing some research online to learn more about what a filament is and why they burn out.

In this unit especially I had to ask more questions than usual, for it was the hardest unit for me to understand. I am not very good with understanding mechanical things; therefore, electricity and current weren't easy for me to understand. Looking for sources for my blog posts was also more difficult than usual, for I would read a website and not comprehend what it was exactly talking about, for there are numerous ways of explaining charges and electricity. By now I feel that I have a more clear understanding of the major terms we learned in this unit, and my effort outside of class is the reason why. 

My goal for the next unit is to spend more time elaborating on my homework questions. Instead of writing simple answers I hope to give more detail into why I think my answer is correct. 

Ohm's Law

Ohm's law states that current in a circuit is directly proportional to the voltage impressed across the circuit and is inversely proportional to the resistance of the circuit.

Current = Voltage/Resistance (I = V/R)

A voltage increases so will the current, and as resistance increases current decreases. The unit which current (I) is measured in is called Amperes (A), and the unit for resistance is ohm.

Voltage

Voltage is how we measure the difference in electric potential energy (∆PE). The two main ideas we covered are electric potential and potential difference.  Electric potential tells us how much work is necessary per unit of charge. Potential difference tells us how much total work is needed to move one charge to another point. The equation used for Voltage is V= ∆PE/q (q= one coulomb of charge). Example problem: If we were to move a charge from point A to point B and we put a number of joules of work in to the charge then we will recover the exact same number of joules in the charge if we move it back from point B to A. The joules of work are neither created nor destroyed, therefore the potential difference remains the same.

Mousetrap Car Challenge

Newtons first law and the mousetrap car: The mousetrap car stays idle until an unbalanced force acts on it (lever arm attached to mousetrap). The car will continue moving until an unbalanced force acts on it, such as a wall or friction.
Newtons second law and the mousetrap car: Acceleration is produced when a force acts on mass. When the mass of the mousetrap car is large more force will be needed to accelerate it, but with less mass means less force needed to accelerate the car, causing it to move faster.
Newtons third law and the mousetrap car: For every action there is an equal and opposite reaction (a=Fnet/m). This means that  acceleration is directly proportional to the net force and indirectly proportional to mass. In order for the mousetrap car to have a greater acceleration, the force acting on the mouse trap needed to be bigger. Also keep in mind that no matter how hard the wheels pushed down on the ground the ground pushed back up with an equal and opposite force.

The two types of friction present in this experiment are static and kinetic friction. A problem that I faced involving friction was the question on whether or not I should use balloon to tie around my CD's to create friction. I wanted my car to move as fast as possible and the thought of adding more friction to my wheels made me think that it would slow it down. I drew this conclusion based off of  newtons second law which states that the car will continue moving until an unbalanced force acts on it. However this assumption was wrong, because without the use of friction the wheels would then just spin in place and not move anywhere. By cutting out stripes from the middle of balloons and wrapping them around the CD's I was able to create enough friction for them to move.

In the beginning I planned on only using three whees, and having the back two wheels be larger than the front wheel, but in the end I chose to give my car four wheels because it seemed to be the best way to keep my car from drifting in other directions. The four wheels were CD's because they are light weight and easy to find. A key component that I added to my wheels was the use of cut out pieces of cardboard which I glued to both sides of the CD's. My two reasons behind doing this was so that I could drill a hole through it to stick the axle in, and because it increases the cars rotational velocity. By adding more mass to the wheels axis of rotation I decrease the wheels rotational inertia and increase it's rotational velocity.

The law of conservation of energy states that the total energy in an enclosed system cannot be changed; energy can neither be created nor destroyed, but can only change form. Knowing this we can conclude that the potential and kinetic energy can transform into one another. In relation to the mousetrap car I knew that the energy exerted from the mousetrap will always remain the same, for it all depended on how efficiently I used this energy. By storing the maximum amount of potential energy the car in turn will have a greater kinetic energy allowing it to go the 5 meters as fast as possible.

For my lever arm I attached a 6 inch pencil to the mousetrap and drilled a hole through it to tie a string around it. Before I decided that I wanted to use a pencil as my lever arm I did some research on it, because I knew that it was going to be a difficult obstacle. While researching I read about how the lever arm controls the cars acceleration, and if I wanted my car to move fast I needed a lever arm that wasn't too long because that would mean less pulling force. Having a long lever arm reduces the speed because it will bend under the tension of the mousetrap spring, thus wasting energy before the car begins to move. A pencil served to be the best possible solution for my lever arm because it is light weight and they don't bend easily. Also the pencil served as getting the most possible potential energy out of the vehicle because of its sturdy structure and large pulling force.

As stated earlier the rotational inertia and rotation velocity plays a key role in how fast the wheels spin. Since rotational velocity is the number of rotations per unit of time, I knew that in order for my car to move fast it had to have a greater rotational velocity. Rotational inertia is the property of an object to resist changes of spin. It is dependent on the mass and how it is distributed, for by having more mass closer to the axis of rotation means less rotational inertia and mass farther away from the axis means more rotational inertia. Tangential velocity is the speed in which a object moves on a circular path, it largely depends on the distance from the axis of rotation. By having larger wheels, they are capable to traveling more distance with less numbers of rotations.

We can't calculate the amount of work the spring does on the car because the force and the distance traveled are not parallel. We also can't calculate the potential energy that is stored in the spring because we don't know its mass or height (PE = mgh). Since we don't know the total energy of the system we also can't calculate the kinetic energy. Change in Kinetic energy = 1/2 mass x velocity and considering we don't know the exact velocity of the spring we can't solve for the kinetic energy.

My final design wasn't completely different from my original design. The only main difference between the two was that I had 3 wheels in my original design. What promoted this change was that I wasn't able to find a smaller wheel to put in the front so I just resolved to using 4 wheels. The only main problem that I encountered was that my string kept getting caught around the back axle, thus stopping my car before it reached the 5 meter mark. My resolution to this problem was cutting off 6 inches, which worked really well, because after doing this my car went 7 meters. If we were to do this project again I would use the mouse trap itself as the base, and I would use just string as my lever arm instead of a pencil.

Here is a labeled diagram of my final mousetrap car: My final times was 4:34 and I came in 4th place in my class.

Here is a video of my car in action: