What is Gravity?

Gravity. Right. The imaginary thing that keeps us on the Earth and everything in order.

There is a big problem though. We know how gravity works and are finding out new and interesting things about it, but do we know why it works?

No. There are only theories of why gravity works.

Take a look at this video below that gives you an overview of what gravity is and how it works.

Warning: You might have to watch it more than once to understand everything the narrator says. The end is especially tricky because those bits of information are probably beyond the scope of your physics knowledge.



Say what?! Did that guy just say gravity also attracts massless objects? How does that work? What is a massless object? Has physics stopped working? Nope. This is a huge part of upper-level physics. Quite interesting.

So tell me, how does gravity effect your life? Can you tell me what a light-year is?

Getting Closer to Sci-Fi?

Your mind will be blown:

http://www.youtube.com/watch?feature=player_embedded&v=Ws6AAhTw7RA

Some of the most basic topics discussed in this video are things you will cover in Physics II: Electricity and Magnetism. The whole idea behind magnets and magnetic fields will seem clearer to you after you take it.

The only thing that went through my mind was Luke Skywalker traveling with his Landspeeder through Tatooine (for any Star Wars nerds out there). Anything is possible if you can think of it. Star Wars may soon become a reality. I call dibs on the pink lightsaber.

Any wild ideas that you guys would like to share?

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.
``

• 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