What is g-force?

A question about g-force. Why?

Atlantis Shuttle Launch:ISS
Atlantis Shuttle Launch:ISS

Simply because Kam’s wetsuit has g-force written across the front of it.  Here is a conversation between Kam and the swimming pool lifeguard.
“hello g-force”
“Hello, why do you call me g-force, my name is Kam”.
“Oh, but g-force is a great name, it’s a super power”.

Oh my, that’s it. Kam, the super powered 4 year old swimmer. (He can swim, he’s competent, and learning his strokes.)

Kam presses his super power button – “Turn on the g-force super power, catch me if you can”.

On the way out of the gym, “mum”, “yes Kam”, “what is g-force and why is it a super power?”……… Oh goodness!

What is g-force?

G force is a rate of acceleration, it measures the rate of acceleration due to gravity of an object falling to Earth.

The rate of  acceleration of objects due to the gravity on Earth is around 9.8 m/s. This means that the speed of something “falling” to Earth increases by around 9.8 metres per second every second until it reaches Earth’s surface.  This is also known as 1 g-force or 1 g.

People suffer temporary vision loss at about 4 g’s, and lose consciousness between 5 and 8 g’s, because less blood reaches the brain.  Body positioning alters the effect a g force has on the body.  As such F1 racing teams and the space industry do plenty of research into body positions, exposure and effects of acceleration relative to g force.

Lateral Acceleration

Roller Coaster, passengers experience 4.5 g force.
Roller Coaster, passengers experience 4.5 g force.

G forces can be felt if there is a change in speed and/or direction.  For example when a car turns a corner, keeping a constant road speed, people inside experience what feels like a force pressing them towards the opposite side of the car.  This is lateral acceleration and is measured relative to 1 g.  For example formula 1 racing cars sometimes generate lateral accelerations of up to 6 g.  This puts a huge strain on the drivers body.

G force Effects

Because of the stresses and strains on objects, large g-forces are very  destructive.

People can cope with intense localised g-forces in the 100s of g’s for a split second, such as a slap on the face. Continued exposure to g-forces above 10 g can lead to permanent injury or worse.  G force tolerance is individual, some people can withstand more than others.

 G force and Astronauts

Astronaut in Launch Position:NASA
Astronaut in Launch Position:NASA

Astronauts experience accelerations many times larger than 1 g.  At launch the speed of a space vehicle increases by 29.4 m/s per second of travel or it accelerates at 3 g.

An astronaut inside the space vehicle endures this g force.  It puts great strain on the astronaut’s body.  Astronauts launch in a lying down position with respect to g force.  This gives them greater resistance to the effects of too much g force pressure, they could withstand upto 20 g for a short time.

G force and Planets

G-force varies on different planets. A body having a bigger mass will have  a higher gravitational field, which results in higher g-forces. For example, the g-force on the Moon is about 1/6 g, and on Mars it is about 1/3 g. (The Moon and Mars have less mass than Earth).

G force – effect of air resistance

If the Earth had no atmosphere, an object dropped from a great height would keep accelerating at a rate of 9.8 m/s every second until it hit the ground.

For example, a silly one, if we dropped a stone from 10,000 m, it would travel at about 442 m/s every second by the time it landed.

In practice, this would not happen because of air resistance. The faster an object falls, the greater the air resistance acting on it. At a certain velocity, known as the terminal velocity, the downward force of gravity is balanced out by the upward force of air resistance and there is no further acceleration.

If there were no atmosphere, all objects would fall at the same rate.  A feather and stone dropped on the moon would fall at the same rate.  On Earth a stone falls faster than a feather because there is less air resistance.

Examples Of G Forces

• Standing on the Earth at sea level, where g force = 1 g
• Standing at its equator on the Moon, with g force = 0.1654 g
• Roller coasters have g forces ranging from 3.5–6.3 g
• Space Shuttle during launch and reentry, g force =3 g
• Formula One car, under heavy braking, g forces = 5 g
• Apollo 16 on reentry, g forces = 7.19 g
• Brief human exposure survived in crash has g forces > 100 g

A note to you and me.

I’m not sure yet
Feeling a bit frazzled!

As ever I hope this post has been informative.  I have tried to summarise g forces and have found it quite challenging!

We’d love to hear from you.  X


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