Gee-Force!!

You have learnt recently that a change in velocity of any object will cause it to accelerate. Acceleration is known as the rate of change of velocity with time. The changing direction, increasing speed, decreasing speed of an object are all factors of acceleration.

In general, high velocity doesn't cause harmful injuries. But what is dangerous is the high levels of acceleration or deceleration over a certain time interval. The common term "G-force" is a measure of acceleration and is not a measure of force eventhough the term 'force' is associated with its name.

Under normal conditions on Earth, a body (standing or sitting) will experience 1G, which is derived from multiplying the body's weight by 1. For example, in roller coasters, the only time you feel 1 G is in the loading station and on the chain lift. Everywhere else, the rider’s body will be subjected to varying G-force due to the dips and crests. Similarly, when a pilot in an airplane changes its orientation rapidly (tight turns, loops, etc.), the aircraft and pilot will undergo additional G-forces.

There are 2 kinds of G-force, positive and negative. They are caused by different conditions and will result in different effects on the human body. For pilots, they will experience positive G-force as the airplane pitches upwards (the nose pulls up) sharply. In roller coasters, the bodies will experience positive G-force at the roller coaster dips or troughs, pushing the bodies into their seats. Under this condition, the blood may rush away from the head to the feet, probably causing greyouts or blackouts to the riders at high G-force levels.

Click here to see a fighter pilot experience a blackout.

For negative G-force, pilots will experience it as they nose dive the airplanes (pitch downwards). Riders in a roller coaster will feel negative G-force at the crests of the tracks where they may experience momentary weightlessness due to the lack of contact force by the seat. Excessive negative G-force will cause the body to experience red-out where excessive blood is pumped to the brain, causing distorted vision. It is normally preceded with a pink-out.

Click here to see boy experience state of weightlessness on an amusement park ride.

Roller coasters give humans a thrill ride. They undergo G-forces of maximum up to 3 to 4Gs for brief periods of time. Pilots on the other hand are trained to undergo accelerations of 9Gs to pull quick maneuvers during flight for less than a second. If a force of 4 to 6Gs is held for more than a few seconds, the results could be devastating; such as blackouts to death. The devastating car crash of Princess Diana of Wales in 1997 was estimated to range somewhere between 70 - 100Gs. This accident was intense enough to pull the pulmonary artery from her heart.

Click here for another interesting video of a pilot experiencing more than 10Gs in his fighter jet.

You may want to explore further on the effects of G-force on the human body and what are some preventive measures that are taken to lessen the effects of G-force on the body especially for fighter pilots. It was said that even sneezing exerts a G-force of 2.5G on the human body. So how much G-force can a human tolerate?

Adapted from :
http://www.furball.warbirdsiii.com/krod/basic-physics.html, http://www.geocities.com/CapeCanaveral/6795/physics.html, http://hypertextbook.com/facts/2004/YuriyRafailov.shtml

What is weightlessness?

Astronauts orbiting the Earth experience sensations of weightlessness similar to that felt by anyone who has been temporarily suspended above their seat on any amusement park ride like the roller-coaster.

Before understanding weightlessness, you must be able to understand the difference between contact forces and non-contact forces. As an example, when you sit on a chair, you will experience two forces, that are the pull of gravity on your body downwards towards the Earth (non-contact force) and the force of the chair pushing you upwards also known as normal force (contact force). Bear in mind that contact forces can only result from the actual touching of the two interacting objects, which in this case is the chair and your rear end. The force of gravity (non-contact force), on the other hand, can never be felt. Therefore, without a contact force, there is no means of feeling the effect of non-contact force.

Weightlessness is simply a sensation experienced by an individual when there are no external objects touching one's body and exerting a push or pull on it. In other words, it occurs when all contact forces are removed like when you are momentarily (or perpetually) in a state of free fall where the only force acting on your body is the force of gravity (non-contact force).

Even when you are undergoing free fall while sitting on a chair, there will be no contact force exerted on you by the chair as it is falling at the same rate as your body. Similarly astronauts and objects in space experience weightlessness as they are constantly falling at the same rate and no contact forces are present.

Here is a video of a dog experiencing weightlessness momentarily as it travelled unbuckled in a plane. There is also a video of how water behaves under weightless conditions.
Click here to view flying dog video.
Click here to view suspended water video.


You may want to explore the internet further for information on what are the effects of weightlessness on human beings especially for astronauts who undergo long periods of weightlessness. You may also want to find out more about common misconceptions about weightlessness.

Adapted from http://www.physicsclassroom.com/Class/circles/U6L4d.html