Roller Coaster

The Infusion at Blackpool Pleasure Beach in Blackpool, England -- a suspended looping coaster

Dave Thompson

Roller Coasters and Your Body

Your body feels acceleration in a funny way. When a coaster car is speeding up, the actual force acting on you is the seat pushing your body forward. But, because of your body's inertia, you feel a force in front of you, pushing you into the seat. You always feel the push of acceleration coming from the opposite direction of the actual force accelerating you.

This force (for simplicity's sake, we'll call it the acceleration force) feels exactly the same as the force of gravity that pulls you toward the Earth. In fact, acceleration forces are measured in g-forces, where 1 g is equal to the force of acceleration due to gravity near the Earth's surface (9.8 m/s2, or 32 ft/s2).

A roller coaster takes advantage of this similarity. It constantly changes its acceleration and its position to the ground, making the forces of gravity and acceleration interact in many interesting ways. When you plummet down a steep hill, gravity pulls you down while the acceleration force seems to be pulling you up. At a certain rate of acceleration, these opposite forces balance each other out, making you feel a sensation of weightlessness -- the same sensation a skydiver feels in free fall. If the coaster accelerates downward fast enough, the upward acceleration force exceeds the downward force of gravity, making you feel like you're being pulled upward. If you're accelerating up a steep hill, the acceleration force and gravity are pulling in roughly the same direction, making you feel much heavier than normal. If you were to sit on a scale during a roller coaster ride, you would see your "weight" change from point to point on the track.

At the top of a hill in a conventional coaster, inertia may carry you up, while the coaster car has already started to follow the track down. Let go of the safety bar, and you'll actually lift up out of your seat for an instant. Coaster enthusiasts refer to this moment of free fall as "air time."

Harris, Tom. "How Roller Coasters Work" 09 August 2007. HowStuffWorks.com. 16 October 2011.

Physics in Cheerleading

THE PHYSICS SIDE TO CHEERLEADING

The Physics……..Newton’s Third Law of Gravity

Newton’s Third Law states that if two objects interact the force exerted on object 1 is equal in magnitude but opposite in direction to the force exerted on object 2 by object 1.

Several forces are present when two objects interact with one another. Body 1’s force on 2 is the action force and body 2’s on 1 is the reaction force. The reaction force accelerates away from the earth and the action force accelerates towards the earth. A normal force is also present which acts in both ways.

The variables present are :

• Fg – the action force (= to mg)
• Fg' - the reaction force
• n-normal force exerting away from the earth
• n'- normal force exerting towards the earth
• Fg ' = - Fg
• N=-n'

The Cheerleading and How it Relates to Physics............

The stunt pictured is a QP. The girl is standing on the guy’s single hand. Notice the normal force present that holds her in the air. In which direction are the action and reaction forces working?

THE SPORT OF GYMNASTICS AND CHEERLEADING:
A cheerleader must become an expert on the physics of rotation. When a she is thrown into the air for a fancy stunt that involves rotation of the body she has all the angular momentum from her push-off that she will get.
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• Angular momentum equals the product of mass, velocity and distance from mass to axis of rotation.
• QUESTION:How can her rate of rotation change without the help of someone giving her a little help or her pushing off on something?
• ANSWER: The angular speed increases or decreases by changing the distance between the mass and the axis of rotation. When a cheerleader performs a stunt, for example, a back tuck, she may have nothing to gain angular momentum(if she stands on the ground with velocity and position both equal to zero. But when she jumps up and tucks her mass in to decrease the distance between her body and the axis of spin. Her angular momentum is still constant because no external torque (radius X force) occurs. Cheerleaders must be in top shape athletically and gymnastics background is often required to do the rigorous routines required today.

MOMENTUM = mass * velocity

FORCE= change in momentum/ change in time

http://www.unc.edu/~reet/physicsside.html

Rotation and Applications

So here I have a video for all of you.



I have a few questions... Hopefully Professor Ellis has not addressed this example in class.

What does the figure skater do to achieve three rotations?
Other than stability, why does she throw her hands out at the end of the rotation?

Interesting Topics in Physics

Hey class!

I was wondering if anybody found a topic in physics they are interested in. As part of my project, I am going to present a topic in physics and I would like to choose something that you all would be interested in. Please leave a comment with a topic that you would like to know more about, or a certain application.

I hope everybody has a good week! For the mean time, check out this video:

You're in for a surprise in that video.

-Brandon Krouppa

Football Physics Force Laws

It happens about 100 times a game in the National Football League: a bone-jarring tackle that slams a player to the turf. On the play shown in the photo above, Seattle Seahawks defensive back Marcus Trufant (23) drilled Philadelphia Eagles receiver Greg Lewis (83) with such force that Lewis couldn't hang on to the ball. (Seattle won the Dec. 5, 2005, game at Philadelphia 42-0 in the most lopsided shutout ever broadcast on Monday Night Football.) Incompletions and fumbles aren't the only consequences of such tackles. More than 100 concussions are recorded each season in the NFL. Given the size and speed of today's athletes, it's surprising that more gridiron warriors aren't carried off the field on their shields. For that, they can thank high-tech gear that protects them from the physics at play in the sport's fearsome collisions.

HALF A TON OF HURT

At 5 ft. 11 in. and 199 pounds, Marcus Trufant is an average-size NFL defensive back (DB). Those stats don't stand out in a league where more than 500 players weighed 300-plus pounds at the 2006 training camps. But a DB's mass combined with his speed -- on average, 4.56 seconds for the 40-yard dash -- can produce up to 1600 pounds of tackling force, according to Timothy Gay, a physics professor at the University of Nebraska and author of The Physics of Football.

HITTING THE DECK

Researchers rate a field's shock absorbency with a metric called G-Max. To measure it, an object that approximates a human head and neck (about 20 sq. in. and 20 pounds) is dropped from a height of 2 ft. A low G-Max means the field absorbs more energy than the player. Trufant and Lewis landed on grass in Philly's new stadium, which has a cushy G-Max of just over 60. Synthetic surfaces have G-Max ratings of up to 120. The hardest turf: frozen grass.

LUGGING THE G-LOAD

Most people associate high g-forces with fighter pilots or astronauts. But common earthbound events can also boost g's. Few things can match the g-load of a wicked football hit.

ENERGY DISTRIBUTION

A tackle with half a ton of force sounds like a crippling blow. But, according to John Melvin, an injury biomechanics researcher for General Motors and NASCAR, the body can handle twice that amount -- as long as the impact is well-distributed. That job usually is handled by the player's equipment, which spreads out the incoming energy, lessening its severity.

BODY ARMOR

According to Tony Egues, head equipment manager for the Miami Dolphins, shoulder-pad plastic hasn't changed much in 25 years, but it is now molded into designs with more right angles to deflect impacts. Players also rely on the helmet's solid shell and face mask to redistribute the energy of a collision.

MEMORY FOAM

During a tackle, foam padding beneath the plastic components of equipment compresses, absorbing energy and reducing the speed of impact. (The slower a hit, the less force it generates.) Visco elastic foam, which was invented by NASA to protect astronauts from g-forces during liftoff, retains its shape better than conventional foam, rebounding rapidly after hits.

SCHOOL OF HARD KNOCKS

According to a Virginia Tech study, a tackle like Trufant's probably caused Lewis's head to accelerate in his helmet at 30 to 60 g's. VT researchers gather data with the Head Impact Telemetry System, which employs sensors and wireless transmitters in helmets. "We see 100-g impacts all the time," says Stefan Duma, director of the university's Center for Injury Biomechanics, "and several over 150 g's."

CHINKS IN THE ARMOR

While Trufant and Lewis generally have enjoyed healthy careers, they (and other players) face the same nemesis: the dreaded knee injury. The knee's anterior cruciate ligament can withstand nearly 500 pounds of pressure, but it tears far more easily from side hits and evasive maneuvers. According to the Pittsburgh Tribune-Review, more than 1200 knee injuries were reported by the league between 2000 and 2003, accounting for one out of every six injuries -- by far the highest percentage in the NFL.

Masamitsu, Emily, Coburn, Davin Football Physics The Anatomy of a Hit
http://www.popularmechanics.com/outdoors/sports/physics/4212171

Newton 3rd Law of Motion

Newton's Third Law

A force is a push or a pull upon an object that results from its interaction with another object. Forces result from interactions! According to Newton, whenever objects A and B interact with each other, they exert forces upon each other. When you sit in your chair, your body exerts a downward force on the chair and the chair exerts an upward force on your body. There are two forces resulting from this interaction a force on the chair and a force on your body. These two forces are called action and reaction forces and are the subject of Newton's third law of motion. Formally stated, Newton's third law is:

For every action, there is an equal and opposite reaction.

The statement means that in every interaction, there is a pair of forces acting on the two interacting objects. The size of the forces on the first object equals the size of the force on the second object. The direction of the force on the first object is opposite to the direction of the force on the second object. Forces always come in pairs - equal and opposite action-reaction force pairs.

A variety of action-reaction force pairs are evident in nature. Consider the propulsion of a fish through the water. A fish uses its fins to push water backwards. But a push on the water will only serve to accelerate the water. Since forces result from mutual interactions, the water must also be pushing the fish forwards, propelling the fish through the water. The size of the force on the water equals the size of the force on the fish; the direction of the force on the water (backwards) is opposite the direction of the force on the fish (forwards). For every action, there is an equal (in size) and opposite (in direction) reaction force. Action-reaction force pairs make it possible for fish to swim.

Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards. Since forces result from mutual interactions, the air must also be pushing the bird upwards. The size of the force on the air equals the size of the force on the bird; the direction of the force on the air (downwards) is opposite the direction of the force on the bird (upwards). For every action, there is an equal (in size) and opposite (in direction) reaction. Action-reaction force pairs make it possible for birds to fly.

Consider the motion of a car on the way to school. A car is equipped with wheels that spin in a clockwise direction. As the wheels spin clockwise, they grip the road and push the road backwards. Since forces result from mutual interactions, the road must also be pushing the wheels forward. The size of the force on the road equals the size of the force on the wheels (or car); the direction of the force on the road (backwards) is opposite the direction of the force on the wheels (forwards). For every action, there is an equal (in size) and opposite (in direction) reaction. Action-reaction force pairs make it possible for cars to move along a roadway surface.

The Physics Classroom

http://www.physicsclassroom.com/class/newtlaws/u2l4a.cfm

Faster Than the Speed of Light?!

So you may or may not have heard the news. A group of scientists at CERN, the world's largest physics lab located in Italy, made a startling discovery. Neutrinos (a sub-atomic particle) travel faster than the speed of light. Here is an article on it:

http://www.washingtonpost.com/blogs/blogpost/post/neutrinos-may-have-traveled-faster-than-the-speed-of-light/2011/09/23/gIQAo04HqK_blog.html

Now why is this a big deal? The speed of light is the ultimate speed; it's impossible for anything to go faster than the speed of light according to the laws of physics. Most of the fundamental laws of physics are based of this fact. This idea was introduced in the early 20th century by Albert Einstein. According to Einstein's theory of special relativity: as you approach the speed of light, time slows down, you become heavier, and you you become flatter. But if there was the possibility of traveling faster than the speed of light then the impossible happens: time goes backwards, you are lighter than nothing, and you have a negative width. This is why people relate relativity and light speed with time travel. I think this is totally bogus and is just shrouded in pretty looking math equations.

I personally dislike Einstein's theories of relativity, so I am VERY excited about this news. I always talked about writing my dissertation to disprove his theories, but that could take a while :). The experiment is being reproduced in a couple other labs in the US and Japan to get the most accurate results and confirm that there were no errors. If they are right, then this will cause all physics books to be rewritten. This can break a lot physics and take us back quite a bit :)

What do you think about this awesome (hopefully true) discovery?

BTW, Speed of light = c = 3*10^8 meters/second = 186,000 miles/second...REALLY FAST

As my idol stated so long ago:

"Einsteins relativity work is a magnificent mathematical garb which fascinates, dazzles and makes people blind to the underlying errors. The theory is like a beggar clothed in purple whom ignorant people take for a king... its exponents are brilliant men but they are metaphysicists rather than scientists." ~Nikola Tesla