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Physics of Mario Kart

Mario Kart was (and still is) the greatest game of all time, and there is a surprising amount of physics involved – not the part about falling off the edge of rainbow road and then magically reappearing back on the track though. Mario Kart uses Newton’s laws. The use of Newton’s first law proves why in order to get moving you have to press a button to accelerate, and when you let your finger off the button, you don’t just automatically stop, you just slow down. Newton’s second law shows how if you use a cart with a greater mass, you need a greater force to get the kart moving with the same acceleration. Mario Kart also uses elastic and inelastic collisions. An elastic collision occurs when two karts run into each other. They both don’t stick together following the collision, but they bounce away from each other. An inelastic collision occurs when two karts collide and the one with the thunder colt transfers to the other kart and now the thunder cloud is stuck to the other kart. While Mario Kart is mostly fictional – with flying blue shells, mystery boxes, and magically coming back to life after falling off into vast darkness – there is still a lot of subtle physics involved.

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Spaceships & EmDrive

Space rockets use thrust in order to get them up into space. Thrust is the sudden, propulsive force of a jet engine, and is based on Newton’s third law. In the rocket, thrust is created from the solid rocket boosters and the main engines. The solid rocket boosters and the external fuel tank are eventually dropped from the rocket in order to reduce mass once in space. The rocket is slowed down a little because of the force due to gravity and the drag force when in the Earth’s atmosphere. NASA has been working on a new way to launch rockets into space: the EmDrive. It is an electromagnetic propulsion drive that generates thrust by bouncing microwaves in a closed container. According to physics, this would be impossible because of the conservation of momentum and that every action has an equal and opposite reaction. However, a group in NASA has been able to generate thrust from the EmDrive in a vacuum. The power of the EmDrive allows spaceships to travel much faster, allowing humans to explore more of space than ever before. If the EmDrive does end up working, the great space exploration could be back on! So for now, we wait.

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Fuse vs. Circuit Breaker

If you live in a house like mine, blowing fuses and circuit breakers is a common occurrence because of all the things we have plugged in at once. A fuse is a small, thin conductor that is designed to separate whenever there is excessive current flowing through the circuit. Fuses are connected in series so that when the fuse blows it will stop current flow throughout the entire circuit. If fuses were connected in parallel, they would not affect the current through any of the other branches. Although fuses are designed to stop all the current flowing through the circuit, sometimes if the voltage is high enough and the fuse isn’t long enough a spark can jump from one end of the wire to the other, allowing some current through and completing the circuit once again (which would not be good at all). Once a fuse is blown, it needs to be discarded and replaced with a new one. A circuit breaker is a switch that automatically opens to interrupt the current flowing through the circuit. When the circuit breaker is on, it allows the current to pass through the circuit. However, when the current becomes too excessive, a strong magnetic force flips the metal lever within the circuit breaker and stops the current from flowing. Unlike fuses, when a circuit breaker is tripped, it can simply be turned back on from the breaker box allowing the circuit to reconnect.

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Newton's Cradle

Newton’s cradle is a device demonstrating the conservation of energy and momentum. In an ideal Newton’s cradle, only the two balls on the end will move and there will be no energy loss, resulting in the cradle going on for an infinite amount of time. However, in a real Newton’s cradle, the fourth ball does have some movement and there is slight reverse movement as seen in the picture above. The equations p=mv and KE=½mv2 can be used to help find the velocities of the two end balls on an ideal Newton’s cradle, with perfectly elastic objects so there is no loss. The type and size of the balls does not affect the solution as long as the material is still elastic and doesn’t have too much mass.

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Physics of Golf

Since The Masters seems to be the only TV program on in my house these past few days, it seems fit to talk about the physics of golf. The angle of the golf club head helps to determine the distance the ball travels in the air and once it hits the ground. The greater the club speed hitting the ball, the lower you want the club face loft angle. This is because you want the golf ball to go farther and not higher. When you are closer to the green, you are more likely to use a higher numbered iron because it has a greater angle and won’t send the ball as far. The dimples on a golf ball also impact the flight path and distance of the ball. The dimples on the ball cause it to have a lower pressure and increase the Magnus effect (previous blog post). If the ball did not have any dimples and was completely smooth, it would have more drag force causing it to not travel as far.

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The Magnus Effect

The Magnus effect happens to a spinning object that drags air faster on one side, which causes the object to move in the direction of the lower-pressure side. Here’s a video showing the Magnus effect in action:   Newton’s third law helps to prove the Magnus effect because the object pushes the air in one direction and the air pushes the body in the other direction, an action-reaction force. With a ball spinning through the air, some of the air spins around the ball with it. The side of the ball traveling into the air slows down the airflow, while the other side of the ball increases the airflow. A greater pressure on the side of the ball with the slow air pressure causes the ball to move in the opposite direction – toward the lower pressure.

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Jet Stream

When I flew to California and back last month, I noticed that it took more time to fly to California than it did to fly back to Rochester (even though it seemed shorter to fly to California because of the time zone difference). This happens as a result of the jet stream. The jet stream is a strong and narrow air current the circles the globe flowing from West to East. Jet streams occur because of the heating of the atmosphere from solar radiation and the Coriolis effect from the Earth’s axis of rotation. Jet streams are used to help aid in weather prediction, because the jet stream causes a lift of moisture in the air, which causes snow to form. Places directly below the jet stream will generally see more snow than other areas. Airlines also take into account the jet stream to predict the arrival times of flights so that passengers don’t miss their next flights. Turbulence on airplanes is also caused by the jet stream, but it doesn’t harm or affect anything directly. Here's an example of how the jet stream can affect the weather:

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Spill Proof Mug

The other day I came across something talking about a spill proof mug. Since I do tend to spill drinks occasionally, I wanted to read about it. The cup uses a suction on the bottom of it to help prevent it from tipping over. Once the mug forms a seal with the surface it is on, the air pressure under it becomes smaller than the atmospheric pressure above the cup, resulting in the downward force keeping the cup on the table. Even when a small force is applied to the top of the cup that would usually tip the cup over, the suction on the bottom of the cup keeps the cup upright.  Here’s a picture of the forces acting on the mug to keep it upright:        

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Earth’s magnetic poles

If you know me well, you know that I have lots of irrational fears that will most likely not happen, knock on wood (I’m also superstitious). One of these fears is that the magnetic poles of earth are switching, ever since I read an article about it in January.  Earth’s poles switch about every 200,000 to 300,000 years, and considering the last major flip was 780,000 years ago, we are long overdue. The magnetic field helps to protect Earth from deadly rays, and if the poles switch, the protection would largely diminish and allow harmful radiation to get to us. Also, the electric grids would fail, meaning that anything and everything that uses electricity would no longer work. Since much of our daily lives is now reliant on electricity, we wouldn’t know how to live without it.  However, it is still possible to survive once the poles switch since groups can come together to help prepare for what might happen and figure out ways to conserve energy  As you can tell from the picture, a pole reversal would be very bad and cause a lot of chaos. So, hopefully, this doesn't happen for a long, long time.  

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Snowboarding Slopestyle

As I watched the Winter Olympics this February, I loved to watch the snowboarding slopestyle and couldn’t help but think of all the physics involved in getting the highest score. When the snowboarders start at the top of the hill, they are full of potential energy. As they make their way down the hill, the potential energy turns into kinetic energy. To create the flips and turns they do in the air, the snowboarders use angular momentum by applying an initial twist in their movement and that helping them spin in the air. They exert a torque from their body onto their snowboard to have the flips in the air. Once in the air, the snowboarders can use their arms to increase or decrease their rotational inertia, which causes them to twist more or less. The low friction of the snowboard on the snow helps the rider to keep their speed while going down the mountain and performing the necessary tricks.

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Air Resistance Tests

Last night my younger brother was watching one of his favorite shows: street science. I happened to walk in the room as they were doing a Galileo-inspired experiment where they were dropping different objects from a crane to show the effects of gravity and air resistance. At first, they dropped a basketball and a bowling ball from a height of 50 feet. Physics tells us that both objects should hit the ground at the same time because in free fall the weight of the object doesn’t matter. However, the bowling ball hit the ground before the basketball, showing the effects of air resistance. Next, they dropped two bowling balls from the same height but with different weights. They wanted to show that, while the shapes of the balls were the exact same, they still wouldn’t land at the same time. They heavier bowling ball took less time to hit the ground than the lighter one, but they were closer in time than basketball and bowling ball were. Finally, they dropped a truck and a refrigerator from a height of 50 feet. They hit the ground at the same time because in that little of a height with that much weight, air resistance does not have much of an effect. If the truck and fridge were dropped from much higher, they would not have hit the ground at the same time because of air resistance. It was pretty interesting to watch the effects of air resistance on different objects!

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Physics in Passengers: Tethers and Zero Gravity

*More spoilers ahead* One of the big scenes of the movie takes place when Chris Pratt’s character Jim is blasted away from the ship while saving everyone on board and his tether connecting him to the ship breaks, leaving him floating in the depths of space forever (or so you think). Many of the scenes involving tethers are actually scientifically correct. Jim and Aurora (Jennifer Lawrence) float with ease while connected to their tethers, and don’t interfere with any of Newton’s laws. While connected to their tethers, they experience no tension because there are no external forces. Another big scene in the movie is when Jennifer Lawrence’s character Aurora is swimming in the pool when, all of a sudden, the power goes out and there is no longer any gravity. Instead of the water floating up from the pool in droplets and Aurora floating into the air, the water moves up into the air all together, with Aurora stuck inside. This is because of the large surface tension of the water, it all sticks together in zero gravity and traps Aurora in the middle of it. Here’s the zero gravity scene:    

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Physics in Passengers: Rotating Spaceship

This past week, I finally was able to watch the movie Passengers starring Jennifer Lawrence and Chris Pratt. As I was watching, I couldn’t help but notice all of the physics involved. *If you are planning on ever watching this movie, continue reading at your own risk, spoilers may be included.* The story takes place in the future, where two of the characters wake up 90 years early from hibernation on an interstellar spaceship. The spaceship the characters are on creates artificial gravity by rotating. The way the gravity is created is the centripetal force from the rotating spaceship. The gravity felt is from the normal force produced, and Newton’s second law states that the gravity created is equal to the centripetal acceleration. The centripetal acceleration is equal to velocity2 / radius. So, a higher centripetal acceleration is created by using a greater velocity or a smaller radius.The Coriolis effect is another way the gravity is felt, which gives an apparent force acting at a right angle to the motion and the rotation axis, creating the effect of gravity. At certain times during the movie, the artificial gravity disappears when the power on the spaceship malfunctions. When there is no power to rotate the spaceship, there is no gravity felt on the spaceship.

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Dog Whistles

The other day my younger brother was using a new dog whistle app on his phone to make tour dog (and me!) go crazy. However, my dad was in the same room and he couldn’t hear the annoying high-pitched sound at all, so my brother was able to get away with continuing the high-frequency dog whistle sound. The highest frequency dogs can hear is 45 kHz, while a child’s limit is 20kHz, and a middle-aged adult’s is 15kHz. Dog whistles range from about 20 to 54 kHz, so it makes sense that I was able to hear the whistle while my dad was not. The equation for frequency is 1/period of the soundwave, or velocity/wavelength. So, higher frequencies are created by a greater velocity of the wave and a decreased wavelength. Waves with different velocities can still have the same frequency if the wavelengths are proportional, and waves with different wavelengths can have the same frequencies if their velocities are proportional. In the video below, it shows the sound waves at different lengths, illustrating the differing velocities and wavelengths at different frequencies – and the different sounds we are able to hear.    

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Rip Currents

When I was at the beach in North Carolina over the summer, for a couple of days there was a sign outside the lifeguard stand that said WARNING: RIP CURRENT. Now at the time I wasn’t exactly sure what a rip current was, all I knew was that it was obviously dangerous and it pulls you out into the ocean. So, I still went in the water because everyone else didn’t seem too worried about it. While I didn’t get pulled out into the ocean by the rip current, I did get a bad sting on my leg from a jellyfish (and it hurt!). Well, rip currents involve radiation stress, which is the force exerted on the water by the wave. Rip currents are powerful currents of water that narrowly run from the beach out into the ocean. They occur when there are variations in the patterns of the waves breaking, and large waves break closer to the shore. All of the water from the crashing wave wants to find the path of least resistance back to the ocean, causing the rip current. The force of the rip current depends on the height of the wave; the larger the wave, the greater the force of the wave, and the greater the force of the rip current. If you ever find yourself stuck in a rip current, don’t panic or swim straight back toward the beach like you would think. The force of you swimming in the opposite direction of the current is not large enough to get you to shore, the rip current has a much greater force. Instead, swim parallel to the shore until you get out of the current, or float out with it, and then once the current stops, swim diagonally back to the beach.

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Sledding Physics

One of my favorite winter activities: SLEDDING! (although not the walking back up part). My house is backed up to the woods and a big hill, so when I was younger we would always go sledding (and try to dodge the trees), and make jumps to go off of on the way down. At the top of the hill, you have the most potential energy because you are at the greatest height. At the bottom of the hill, you have the most kinetic energy because you are moving the fastest and all the potential energy has turned into kinetic. Sledding only works when there is snow on the ground, if you try to go sledding on a grassy hill it won’t be as fun because snow helps to eliminate friction. Snow has a lower coefficient of friction than grass, so the force of friction will be smaller, and you will go down the hill faster. The normal force and gravity are the main forces during sledding, so the more you weigh, the greater the force will be and the faster you will sled down the hill. Also, the steeper the hill, the faster you will sled because with a greater angle there is a greater force. Sledding is much more fun when you’re going fast, so if you like having fun and moving fast, sled on snow or ice, increase your weight, and find a steep hill to go down!

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Christmas Physics

Even though it is well past Christmas, I figured why not use physics to try to prove a myth that many kids believe, the myth of Santa and his reindeer. While Santa is said to have magical abilities that allow him to deliver presents in one night all over the world, let’s pretend that Santa doesn’t have magic and he just obeys the laws of physics. So, Santa has to visit around 500 million houses in the span of 31 hours (taking into consideration different time zones and the rotation of the Earth) and deliver at least one present to at least one child. This means that Santa has to visit about 4480 houses per second, or spend .0002 seconds at each house. In order to travel fast enough to make this trip in one night, Santa would have to travel at around 6500 mph, which is completely doable (in a rocket). Since Santa would be travelling this fast, he would definitely need some type of heat shield for himself and the reindeer to endure trillions of joules of heat, or else he would just be a flaming ball shooting through the sky. Now, what about all the cookies and milk? Well, these could *easily* be converted into energy to fuel his sleigh using the equation E=mc2. So, I guess Santa could be real, it’s just not very plausible. It’s much easier to just stick with the Santa has magical abilities thing! Check out this fascinating article that goes much more in-depth than I do (it uses different numbers than me as well): https://www.snopes.com/holidays/christmas/santa/physics.asp

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Sulfur Hexafluoride

One of my younger brother’s favorite shows to watch is Mythbusters, and repeats are on almost every day. Well, a couple of days ago I saw a video about inhaling sulfur hexafluoride. Everyone has heard someone talk after inhaling helium from a balloon, they sound really funny because their voice is very high. The effect helium has on the voice is because it is much less dense than air. It causes the speed of the sound of your voice to increase, whereas the frequency of the vocal cords doesn’t change. Inhaling sulfur hexafluoride has the opposite effect of helium, it causes your voice to go extremely deep, like Darth Vader. This is because it is much denser than the air we breathe in, causing the speed of sound of your voice to decrease while the frequency stays the same. It is really entertaining and amusing to watch someone talk after inhaling sulfur hexafluoride!  

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Spikeball Physics

Spikeball is one of my favorite games to play in the summer, and I'm really wishing it was warm enough to play right now! Spikeball is a game involving a hula-hoop sized net placed on the ground and 2 teams of two go back and forth hitting a small ball across it. It can be played anywhere, including the beach, the grass, maybe even the snow if you're willing to get cold! Much like volleyball, each team has 3 alternating touches to hit the ball on the net for the next team to then play. However, there are no distinct "sides" each team is allowed on, and once the ball is served, there are no boundaries to where you can move. In order to score a point, the opposing team has to make a mistake by hitting the rim, missing the net, using more than 3 touches, causing the ball to bounce more than once on the net, or letting the ball hit the ground. Now, for the physics involved, each person must add an applied force to the ball in order for it to bounce across the net. There is much trial and error involved at first to see how much or how little force you need in order to score a point, depending on the position of the other team. Once the ball hits the net, an equal and opposite force is applied, causing the ball to bounce back up. However, this depends on how tight or how loose the net is, much like a spring constant. The tighter the net, the greater the force the ball will bounce back with; the looser the net, the less force the ball will bounce back with. The force also depends on the mass of the ball; therefore, the more air that is pumped into the ball, the greater the force the ball bounces back with. Check out this awesome video of spikeball in action:  

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The New Year's Eve Ball "Drop"

As you may know, people ring in the new year every year by watching the events taking place at Times Square, most importantly the ball drop starting one minute before January 1st. However, calling it a "ball drop" is a tad misleading because it doesn't actually free fall to the ground, the 11,875 pound (5386.4 kg) ball slowly descends down a 43 meter tall flagpole in the span of 60 seconds. It is not as stunning as everyone makes it out to be. Sure, the ball is made up of 2,688 crystals, but it doesn't fall to the ground and shatter into a million pieces, which would be much more breathtaking to watch in my opinion. If the Times Square Ball were to drop from 43m, without air resistance, the ball would crash to the ground in 2.96 seconds. In order for the ball to free fall to the ground in the same 60 seconds that it takes to go down the flag pole, the ball would have to be dropped from 17,702 meters in the air, which is about 11 miles. Most planes don't fly any higher than 12,000 meters, or 7.5 miles, in the air. This means that if the ball were to free fall to the ground in 1 minute, it could potentially hit a plane on the way down, and who knows how anyone could ever get it up that high in the first place. I guess now I realize that it makes sense for the ball to go down a flagpole instead of free falling in 60 seconds!

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Top-making

In physics class earlier this week, we were presented with a task to make a top out of two mini paper plates, a pencil, six pennies, and tape. Without any instruction, we had to create a top and make it spin for a decent amount of time using these materials. The engineering design process played a big part in our creation of a top, even though we didn't know it at the time. The steps of the engineering design process are: define the problem, do background research, specify requirements, brainstorm and choose a solution, develop and prototype a solution, test solution, solution meets requirements, and communicate results. The problem was to create a top and the background we had was we saw one working before we started to design our own. The brainstorming area had to be cut short based on time, so we went right into making our solution. Once our first solution didn't work out as we were testing it, we mostly resorted to trial and error. While we were never successful in getting the top to spin for more than a couple seconds, some of our classmates were. A top relates to moment of inertia and angular momentum because the moment of inertia depends on mass and radius, so including all of the pennies spaced out to the edges of the paper plates created the most inertia. Angular momentum depends on the moment of inertia and angular velocity, so the greater the inertia and angular velocity, the greater the angular momentum, and therefore the time the top will spin. I now understand the difficulty of the engineering design process and how many tries it takes to finally come up with a perfect solution based on the proper equations.

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Physics of Fetch

A dog trying to catch a ball in its mouth is like a person trying to catch a football, a lot of coordination and timing. Kinematics could be involved to find the distance, but there is not enough time for a dog or person to calculate that since it only takes a couple seconds for the ball to reach the dog. However, if you ever did want to find the distance, you would need both the x and y components of the initial velocity, acceleration in the y which is equal to 9.8 m/s2, and the time it takes for the ball to reach the dog. It would be a little more complicated than a simple kinematics problem since there is the height of both the person and the dog to take into account. When I was in Target the other day, I saw a new toy called the Chuckit which is basically just an extension of someone's arm that you can put a tennis ball in in order to throw it farther. Using the equation torque=Force*radius, the Chuckit increases the length of someone's arm and therefore the radius. By applying the same amount of force, the person can throw the ball much farther by using the Chuckit because of the increase in torque. So, if your dog isn't getting enough exercise from you just throwing the ball, add more length to your arm to throw it farther!

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Falling Penny vs. Falling Pen

I'm sure everyone has heard the myth that if a penny is dropped off the Empire State Building it could kill someone. Well, fortunately you can still walk in NYC without shielding your head from falling pennies because this is not true. The penny will tumble as it falls which will slow it down, and because pennies are flat and thin, they experience a lot of air resistance opposing the force of gravity. A penny would reach a  terminal velocity of a meager 25 mph at 50 feet. Instead of going straight into your head like most people believe, the penny would bounce right off and you would most likely only feel a small sting. If air resistance didn't exist, the penny would reach 208 mph by the time it reaches the ground, which could definitely do some damage. However, don't go walking around without your head covered just yet. A pen that is dropped perfectly vertical from the skyscraper would reach a terminal velocity of 200 mph, and would most likely kill you. Because of the narrow, cylindrical shape of the pen, it would fall like an arrow and pierce your skull, killing you. Now, if you're like me, you will want to walk around with a helmet on for the rest of your life in order to avoid a hole in your skull from a stray pen!

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Physics of Angry Birds

While the once popular cell phone app reached its peak a couple of years ago, Angry Birds is a great example of projectile motion. The basic goal of the game is to launch the birds using a slingshot to knock out the green pigs. In order to knock out the pigs with the least amount of shots, you need to launch the birds with the correct initial velocity and at the correct angle. There are multiple different birds that are used in each level, including the standard red bird, a blue bird that turns into 3 birds when tapped, a yellow bird that changes to a faster velocity when tapped, a white bird that shoots down an egg when tapped, a black bird that blows up when tapped, and a green bird that turns into a boomerang when tapped. If we only look at the standard red bird, we can infer that the app does not take into account air resistance since the bird follows a parabolic path. Therefore, the horizontal component of the velocity stays the same and the vertical component of the velocity changes because of the acceleration due to gravity. The kinematics equations vf=vi+at , x=vit+1/2at2 , and vf2=vi2+2ax can be used to solve for the distance the bird will travel both vertically and horizontally using given variables. In order to cause the greatest damage, it is best to pull the slingshot back as far as it will go in order to have the greatest initial velocity and travel the greatest distance. Now playing Angry Birds should be much easier considering the projectile motion we have learned and how to calculate the correct initial velocity at the right angle in order to get the bird to travel the correct distance! While you most likely won't do any actual calculations, your estimations should be much closer and will hopefully help you get a higher score!

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Do billiard balls hurt?

Put simply, the answer to this question is yes. But here's how I found out: The other day, I was playing pool in my basement with my brother and, of course, I was looking at something on my phone just as the cue ball was hitting the 9-ball and he applied so much force that the 9-ball bounced off the table and landed right on my foot. It hurt really bad and I still have a large bruise right on the top of my foot. Well, since a standard billiard table is .762m and we can use acceleration as 10m/s2 and the billiard ball started from rest from the top of the table, the final velocity that the ball hit my foot with was 3.9m/s. Ouch. A billiard ball's mass is .17kg, so the force that it hit my foot with was 17N. Ouch. Needless to say there is a large bump on my foot from the ball and now I will always pay attention the playing pool with my brother since he clearly doesn't understand physics well enough to be able to hit the ball with enough force that it will still move, but not too much force so that the ball won't end up on the ground.

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