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...

br />

 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.

/
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.