Ten times you see physics at the beach

With summer vacation on the horizon, the beach is on everyone’s mind. Here are ten times you would see physics at the beach

 I. Inertia- driving away without your sunscreen

When you go to the beach, you have to wear sunscreen to protect yourself from harmful UV rays. Say you are in your driveway packing up to go to the beach, and you put a bottle of sunscreen on the hood of your car. If you forget that it is there, and drive away with it still on your hood, it is going to fall to the ground and you will get burnt at the beach. This is because of Newton’s First Law, which states that objects in motion stay in motion and objects at rest stay at rest unless an unbalanced force acts upon them. Essentially, objects will keep doing whatever they are already doing because they are “lazy” if you will. When the car and sunscreen are parked, they are both at rest. However when the cars starts to move, it is in motion while the lotion stays at rest, because it wants to keep doing what it was previously doing. The car pulled out from under the lotion, and gravity pulled the lotion to the ground.

 II. Throwing beach volleyball (free fall)

Playing volleyball on the beach can be fun. When you throw a ball up in the air and it slows and begins falling down towards earth, it is in free fall. Free fall is when objects fall due to the acceleration of gravity. All falling objects fall at a rate of 9.8 meters per second squared. Check out this diagram to see the path, including velocities the ball traveled at certain times during its flight.

III. Speakers, Electromagnetic Induction, and Reggae music
When you get to the beach, playing reggae music really helps to set the mood. But to play music, you must have a set of speakers. Speakers work through electromagnetic induction, which is a method of inducing a voltage and current to create sound. In a set of speakers, there is a magnet and a series of wire coils. The interaction between the wire and magnet change the magnetic field of the system, which induces a voltage and then induce a current. The current acts as a signal which moves a cone within the speaker, which produces sound so you can listen to reggae music at the beach!

Here’s a great reggae band I'm into right now...

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 IV. Fishing: you pull fish, fish pulls you (Newton’s Third Law)

When I was little, I used to fish with my dad on the shore, and sometimes I would reel in really heavy fish. When you have a big fish on the line, you would assume that the fish is pulling you with a stronger force than you are pulling it because you can literally feel it moving you. However, this assumption is incorrect. Newton’s Third Law states that every action has an equal and opposite reaction. Though it may be hard to believe, you are exerting an equal force on the fish as the fish is exerting on you. The reason why you can feel the fish physically pulling and moving you is because you are experiencing a greater acceleration. This can be explained by Newton’s Second Law, which states that mass is inversely proportional to acceleration, and force is directly proportional to acceleration.


V. Why does the fish pull so hard??

Newton’s Second Law a=f/m
Since the forces of the fish and you are the same, this means that the acceleration and mass are inversely proportional. Since the fish has a smaller mass than you, it will have a larger acceleration than you. And similarly, since you have a larger mass than the fish, you will have a larger acceleration than it does. This larger acceleration will cause you to move.


VI. UV Rays
Golly gee! Since you forgot about your sunscreen on the hood of the car, you are starting to get a little pink. UV rays are harmful ultraviolet light that enter earth’s atmosphere and can be very damaging to your skin. In order for a force to be felt, charges have to be moving perpendicular to the earth’s magnetic field. This means that in theory, you can feel slightly more UV rays at the poles than at the equator. When you are at the poles of the earth, charges are moving parallel to the earth’s magnetic field. Since no force is felt, UV rays can enter the earth’s atmosphere easier than at the equator, where charges move perpendicular and the force keeps them out better.


VII. Motors and boats

Boating is one of my favorite activities during the summer. But a motorboat would never work without a motor. All motors operate upon the same principle, that consists of a current carrying wire and a magnet. When a current runs through the wire, a force is felt from the magnetic field, and causes a torque and the motor runs. Remember that a torque is basically a factor that causes an object to rotate, so when the motor rotates, this causes the propeller to spin, which moves the water and makes the boat run.


VIII. Beach ball vs. bocce ball
Playing bocce ball or throwing around a beach ball is another fun past time at the beach. If you tried rolling a bocce ball and a beach ball at the same time, you will notice that the bocce ball rolls faster than the beach ball. This seems misleading though, because the beach ball is so hollow and light, whereas the bocce ball is so heavy. The reason the bocce ball rolls faster is because its mass is positioned at the axis of rotation (middle), so it has less rotational inertia. The beach ball has more rotational inertia because its mass is located far from the axis of rotation.


 IX. Tides

Depending on the time of day when you are at the beach, you will notice that the water starts receding out towards the horizon, or it might come closer into shore. These changes in water levels are called tides. When the moon exerts force on the earth, uneven amounts of force are created on opposite sides of the earth. The side of the earth that is closer to the moon has a larger force, and the side farther from the earth is less affected by the moon’s gravitational force. These opposite forces create a “bulge” around the earth, which creates the tides. Over a period of 24 hours, there are four tides. Two high tides lasting six hours each, and two low tides lasting six hours each. The tides can affect what you do at the beach, because at extreme high tides there is sometimes no sand left to stand on.


 X. Lighting

I think it’s funny when it starts raining at the beach, then people run out from the water, as if they weren’t already wet. Anyways…
Sometimes when you go to the beach in the summer, it will start to thunder and lightning. During a lightning storm, the clouds in the sky become negatively charged through friction. The negative charges in the sky induce positive charges in the ground. Since opposite charges attract, the positive charges creep up through the sky towards the clouds and if the circuit is complete, energy rushes up from the ground into the clouds. This energy is released in the form of light that produces lightning, sound that is the sound of thunder, and heat. So next time you go to the beach, think about all the physics involved

Windmill

Background
In order to understand how a windmill works, you must first understand how electromagnetic induction works. Electromagnetic induction is when a magnet changes the magnetic field of a series of wire coils. This change in magnetic field induces a voltage, and hence induces a current. All of this happens in the generator of the windmill. The generator we build consists of a series of magnets revolving around coils of wire when the system spins from the wind.

Materials, Methods, and Construction
From a construction stand point, our turbine was build out of a 2 liter soda bottle, which we cut slits into to create fan blades that protruded out of the system. These flap like structures collected the wind when we turned on the fan. We wrapped wire coils and connected them together with electrical tape. It is important to make sure the wires are all facing the same direction, so current can move throughout the entire system. We put the wire coils on a circular wooden platform, and put the magnets on another wooden platform. We put a small barrier between the two, so there would be space and the magnets wouldn’t stick to the wire, allowing the object to spin freely. To connect the whole apparatus, we strung a string through the top of the bottle, down through the bottle and down both wooden platforms. We hung the bottle from the top of a cardboard box, so the windmill could stand stationary.

Results
We ended up generating 0.003 amperes of voltage. However, we tried making our fan blades larger by adding cut pieces of soda bottles, and this unfortunately generated less electricity. We were not able to light a lightbulb, we would have needed 10 times the amount of electricity.

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Reflection
I think if we had reduced the amount of friction of the system, it would have rotated easier and generated more electricity. We ran through a couple bumps in the road. One of which was when we  were attaching the platforms of wire and magnets, the magnets wanted to stick to the wire, and the system resisted to move. We  fixed this by creating a larger barrier between the magnets and wire. Also, every time we turned our fan on, the windmill would fall off its base after about 4 seconds. We realized that each individual piece of the system needed to be held together down the center. To remedy this, we threaded a string down the cap, through the bottle, and through both the platforms. After this, the windmill was stationary when the wind blew it. Problem solved.

Unit 7 Summary

MAGNETISM

àThe source of magnetism is moving charges

àMagnetic force is the force due to the motion of charged particles

àMagnets are clouds of magnetic charges

In order for a force to be felt, the magnetic field must be perpendicular to the movement of electrons

For example, cosmic rays are felt at the poles because charges are moving perpendicular to the magnetic field, and parallel at the equator.

Magnetic field lines of a magnet

àCompasses are magnets that are free to respond to the magnetic field of the earth

Why does a paperclip stick to a magnet?

The domain of the magnet is a cluster of spinning electrons. The magnet has a magnetic field, and the paper clip has a random domain. When the two come in contact, the domain of the clip align and match the magnetic field.

Now the paperclip has a north and south pole. The opposite poles of the clip and magnet attract each other, so it sticks

Demagnetized vs. Magnetized domains

MOTORS

All motors depend on a magnet, and a current carrying wire. The wire must feel a force in the magnetic field and cause a torque in order for it to spin. Remember, that in order for the wire to feel a force, it must be moving perpendicular to the magnetic field. In a motor, electrical energy is converted to mechanical energy.

ELECTROMAGNETIC INDUCTION

Electromagnetic induction is a method used to induce a voltage by changing an object’s magnetic field, and hence inducing a current.

More specifically, when magnets revolve around a series of wire coils, the magnetic field is changed in order to induce the voltage and current. The current is typically used as a signal or message, which operates everyday objects.

Every time I played an electric guitar, I didn’t realize that the sound was produced through electromagnetic induction. There are metal coils underneath the pickups of the guitar, fixed with small pickup magnets. When you pluck a metal string, you change the magnetic field with the vibrations. Since the magnetic field has changed, both a voltage and a current have been induced. The current sends a signal to the amplifier (connected to pickups) and then releases sound.

(P1)

These signals can also be used in metal detectors, stop light signs, and credit card machines. I really enjoyed learning about this because I was able to relate it to my everyday life so easily, given that I shop too much and play guitar J

GENERATORS

A generator is a rotating coil within a stationary magnetic field. They essentially depend on a magnet to change the magnetic field. The way this works is by sticking a magnet in and out of a wire loop, which alternates the direction of the voltage.

TRANSFORMERS

The objective of a transformer is to change the voltage of a system. This works by changing the magnetic field of the primary (AC) current which will change the magnetic field of the secondary (DC). It is important for the loops of the primary to have alternating current, that way the magnetic field has the opportunity to change.

Motors

In a nutshell, a motor consists of a current carrying wire and a magnet. For the motor we build in class, we attached bent paperclips to the poles of a battery. We fixed a loop in the middle of the copper wire, and it rested on the paperclips.

When a current runs through the wire, a force is felt from the magnetic field, which causes a torque and then causes the motor to run. The reason a torque occurs is because the charges are perpendicular to the magnetic field. If they were parallel, there would be no force, no torque, and therefore no operating motor.

This is why we scraped the wire on the top section (longwise facing the ceiling), so the charges would be perpendicular to the magnetic field and cause a torque.

Even the most complicated motors start with this simple model involving the magnet and wire. Motors can be used to power drills, cranks, or any object that requires rotation.

Unit 6 Summary

CHARGES AND POLARIZATION This video discusses charges, the different types of polarization, and Coulomb’s law. Watch to learn about how lightning works, and why balloons stick to walls after you rub them in your hair. Please excuse the poor quality :/ ELECTRIC FIELDS AND ELECTRIC SHIELDING → Electric fields are areas around a charge that can have an influence on another charge → Electric shielding is when charges distribute evenly amongst each other, and the charges inside the field experience no force

The arrows around charges show which way the charge is pushing. The closer the lines are, the stronger the electric field. Metal boxes act as electric shields. Metal allows charges to evenly distribute. The charges in the outside field are pulling the charges in the box with equal and opposite forces. Since the contents of the box experience no force or movement, they are safe. OHM’S LAW AND ELECTRIC POTENTIAL DIFFERENCE →Electric potential energy- energy that is stored within electric fields →Electric potential and voltage are used synonymously

Both are measured in volts →Ohm’s Law Ohm’s Law deals with the relationship between voltage, current, and resistance

It is easy to confuse volts and voltage. Remember that volts are the same as electric potential (pe/charge or J/C) Voltage causes current, and is the difference in electric potential. What are capacitors? → Capacitors are two plates fixed with opposite charges. Charges are added to each side, and the electric field and energy increases between them. Energy then rushes from one plate to the next through a wire, and energy is released in the form of light. Capacitors are often used as camera flashes CIRCUITS In order to have a complete circuit, you must connect 2 uneven electric potentials to cause current to flow. Here are the two main types… →Series

→Parallel

→Fuses Fuses are added to parallel circuits (since they can have more current running through them), but are wired as a series. When too much current runs through the circuit, the fuse will break. This will cut current from all devices to prevent fires, because too much current creates a lot of heat. →Calculating current and resistance

Mousetrap car, you don't go very far...

We were assigned to build a mousetrap car which could travel a distance of five meters. This project was very challenging, but at the end our car ended up going 5.21 seconds in five meters. 

We hot glued to mouse trap to a wooden platform, and attached axels on the back and front by drilling holes and securing them with eye bolts. We fastened a colored pencil to the trap as our lever arm, and attached the string from the pencil to the back axel using zip ties. When the string is would around the back axel, the lever arm pulls the string forwards, and the back wheels move with it. 

THE PHYSICS

àNewton’s First Law

Newton’s First Law states that objects in motion will stay in motion and objects at rest stay at rest until an unbalanced force acts upon it. According to this law, the car would supposedly stay in motion forever, however friction acts on the wheels causing it to stop eventually.

àNewton’s Second Law

Newton’s Second Law states that acceleration is directly proportional to force, and is indirectly proportional to mass. In terms of our car, if we had a larger force causing it to move, it will have a larger acceleration. This also means that the more mass the car has, the harder it will be to accelerate.

àNewton’s Third Law

Newton’s Third Law states that every action has an equal and opposite reaction. In this case, the action reaction pair is the car pushing the ground backwards, and the ground pushing the car forwards

àFriction

Friction is caused by weight and quality of the surface. The first time we rolled our car, we noticed that the wheels weren’t gripping to the ground like they should have been. In order to remedy this, we applied a few layers of electrical tape so that the wheels would have more traction and would move better across the floor. Although we wanted friction on our wheels, we didn’t want it on our axel. We applied vaseline to the axel to get the string to pull off more easily with less resistance. Both of these small changes related to friction helped the car move more efficiently.

àWheel size

Originally, we had two large wheels made of CD’s in the back, and two very small wheels in the front. Even though all of the wheels moved well and were stable, the difference in size of the two sets of wheels were an issue. Both sets of wheels had the same rotational velocity, or number of revolutions per second. However, the back wheels had a smaller tangential velocity than the front wheels, because they are larger. The smaller front wheels had a larger tangential velocity in order to cover a much larger distance to keep up with the back wheels. Since the front wheels were spinning so much, they weren’t really taking the car anywhere. We decided to replace the small wheels with larger ones, which solved the problem and helped the car travel another 2.5 meters.

àLever arm

The lever arm was attached to the mousetrap, and essentially is what made the car go. A torque is factor that causes an object to rotate.

Torque=lever arm x force

Essentially, we want a smaller lever arm, because this will cause the force to be greater, which will propel the car forward faster. Furthermore, the lever arm increases the time and distance that the force is acting on the axel. However, I you have very large wheels, you must have a longer lever arm since you will have a large rotational inertia

àConservation of energy

It is important to remember that energy can be neither created nor destroyed. It can however, be converted into different types of energy such as kinetic (movement) and potential (position) energy. When the car was at rest, it had a certain amount of potential energy. Then when the car started speeding up, some of that potential energy was gradually turned into kinetic energy. As the car slowed down, some of its kinetic energy changed back to potential energy. However, the amount of energy remained the same the whole time.

àWork calculation

Interestingly enough, the car was actually not doing work before, during, or after if moved. We know that work equals force times distance. But it is very important to remember that force and distance must be in the same direction in order for work to be done. The spring acting downwards on the car is not work, because the car moves forwards.

REFLECTION

As stated earlier, the only drastic design change was switching small wheels out for larger ones. Smaller things like adjusting lever arm attachments, and dealing with friction were other things we did to improve the car.

The biggest problem with our car was when in the beginning, it would not go in a line, but rather in a complete circle. This was because one of the back wheels wasn’t touching the ground completely when it rolled. To fix this, we applied a few layers of tape around the wheel to make it taller. We also added a little weight to the side. These fixes corrected the turn, and we finally got the car to move down the hallway.

If I were to do this project again, I would research more and develop a solid plan before beginning. We didn’t really know what we were doing at first, and more organized planning would have benefited us greatly in the end. 

Unit 5 Summary

WORK AND POWER Work=force X distance →Work is measured in joules, and the force and distance must be parallel in order for work to be done So walking up the stairs is doing work, but holding an object above your head (force upwards) while walking across the room is not doing work, since the force and distance are in different directions. Power=joules/seconds Measured in watts →time is a factor in power, unlike time If you push a 20N box for 10m in 5 seconds, how much work and power are you generating?

Check out our video! WORK AND KINETIC ENERGY Energy is the ability to do work, which requires both mass and speed Work = change in kinetic energy

Kinetic energy is energy that requires movement. Remember that... KE final- KE initial= change in KE Potential energy is energy that does NOT require movement, but rather height (position of object). Here are the formulas for the two…

A 100kg car travels 10 meters in 5 seconds. Find the kinetic energy

Unfortunately, the car falls off a cliff and falls 200 meters to the ground. Find the potential energy of the car.

CONSERVATION OF ENERGY Change in kinetic energy = change in potential energy Work = f x d Work in = work out (Force in)(Distance in)=(Force out)(Distance out) energy in= energy out Say it takes 500 joules of energy for a roller coaster to run. From start to finish, the roller coaster will have 500 joules, because energy cannot be created or destroyed. However, energy shifts from potential (height) to kinetic (movement) depending on the position of the cars.

As you can see in the diagram, when the roller coaster is higher up on the tracks, it has a higher potential energy because it has height. Similarly, it has more kinetic energy at the bottom because it is in motion, and has less height. Why do airbags in cars keep us safe? When in a car crash, you go from moving to not moving despite how you are stopped. So whether you hit a tree, a brick wall, or a person, your change in kinetic energy is going to be the same. Remember… Ke= 1/2mv^2 Change in KE= Ke final- Ke initial If the change in KE is the same (which it is) so is the work. The airbag will increase the distance that the force acts on you, so the force will be smaller. Less force= less injury

MACHINES The purpose of a machine is to increase the distance at which an object moves, while decreasing the force used to move it. It is important to remember that machines do not change the amount of work done, they just make it easier since you don’t have to use such a great force to accomplish your task. (insert diagram) Work= fd (insert ramp diagram) work out (small distance) work in (big distance) work in= work out no change in work Say you have to lift a 20N refrigerator 5 meters onto a moving truck.

The work out is always the smaller distance, and the work in is the larger distance.

Remember that machines do not change the amount of work done. They just redistribute the amount of force you exert the object over a certain distance. —>So even though energy is conserved, you can never get more work out of a machine than you put in. In fact, it is impossible for a machine to be 100% efficient. This is because some energy escapes through the form of sound and heat. Efficiency= workout/work in x 100