Creating G FORCES!
G forces are the reason to ride a roller coaster. There are three types:
Positive G's: When riding a roller coaster, riders will sometimes feel very
heavy in their seats. This feeling is caused by positive G's. Positive G's
occur at the bottom of most hills and depend on how fast the coaster
levels off. One G is the pull of normal gravity. Currently, we are all at one
G, we experience this as our own weight. But if we're on a roller coaster,
we can experience up to five G's (that feels like your own weight has
grown five times!) When the coaster train levels off, riders are still moving
down. This is when positive G's escalate. For example, let's say that there
is a boy that ways 100 pounds. That is his weight at one G. At two G's the
boy will feel like he ways 200 pounds. At three G's he will feel like he
weighs 300 pounds. This continues as the G's increase. Most roller
coasters pull about 4 G's. Some coasters pull five G's or even six. Once a
person is at five G's, he/she is likely to black out because the heart has to
pump five times as hard to get the “heavier” blood to the brain. At nine
G's a person could die from lack of oxygen reaching the brain. Nothing
pulls more than five G's except for fighter jets. Pilots can pull up to nine G's
only because they have a G suit which will keep the blood flowing
through out their bodies.
Negative G's Negative G forces are the opposite of positive G's. These
occur when cresting a hill on a roller coaster. Anything below one G is
considered a negative G. At zero G's a person experiences a feeling of
weightlessness. This occurs because on the uphill, you are still going up,
while the train is trying to go down. This creates the common 'butt out off
seat' experience. Roller coaster enthusiasts call it “air time”. Essentially,
negative G's are a resistance of a force of gravity, since your moving
upwards, not down. Negative G's don't end at zero G's. They continue
going up with -1, -2 and upwards. As the numbers get lower, (i.e. larger
number with a negative in front of it) the more force is acting upon you.
The sensation you feel is that you are getting sucked out of the roller
coaster train. You are kept in, though, by the restraints and the force of
gravity which is usually strong enough to hold you in the car without the
restraints. In my opinion, negative G forces are the best because of the
“air time”. That's what a roller coaster is all about. However, too much
negative G’s can cause a red-out. This is the opposite of a black out.
Your heart is able to pump blood so efficiently that you actually flood the
brain with too much of it. This is only dangerous if it goes on for a long
time or if you have an undiagnosed blood clot. Under extreme negative
G’s such a clot may be able to break loose and cause a stroke (blockage
of blood to the brain). A healthy person shouldn’t need to worry about
this but sometimes we don’t know we have these conditions until
something bad happens. So there is always a risk when you get on a
coaster. However, for most healthy people the risk is very small.
Lateral G's A lateral G is the force that pushes the riders to the side.
Lateral G's occur when the roller coaster is making a sharp turn left or
rigth. Your body is going straight, but the coaster is turning. Banking the
turn (tilting it) helps reduce some lateral Gs. Most of the coasters today
have seat dividers which reduce lateral G's. In fact, some coasters have
special seats that reduce the lateral G's. Older coasters didn't have seat
dividers, which allow riders to slide across the seat and into their riding
partner. If your riding partner is big like me you could get smushed! I call
that the Stracuzzi G force.
Weightlessness
Weight is the pull of gravity on your mass. Typical weight units are pounds
and Newtons. (1 pound is around 4.45 Newtons). On the moon, gravity
pulls with 1/6 th the force compared to the Earth. Therefore, a student on
the moon weighs 1/6 of what she weighs on the Earth.
On the Earth, neglecting air resistance, all objects will speed up at a rate
of 9.80 m/s every second they fall. That is a speed increase of about 22
mph for every second an object falls.
Time in the Velocity
Air
(s)
(mph)
0
0
1
22
2
44
3
66
4
88
5
110
There are two ways to experience weightlessness. (1) move far enough
away from the planets and sun to where their pull is nearly zero. [Gravity
acts over infinite distance. One can never completely escape it.] (2) Fall
down at a rate equal to the pull of gravity. In other words, accelerate to
the Earth speeding up 22 mph every second in the air. In order for a
person to feel weight, a person must sense the reaction force of the
ground pushing in the opposite direction of gravity.
In the absence of the reaction force a person will sink through the ground.
Many amusement park rides generate the weightless sensation by
accelerating down at 22 mph every second.
g’s
Neglecting air resistance, if a rock is dropped, it will accelerate down at
9.8 m/s2. This means it will speed up by 9.8 m/s for every second it falls. If a
rock you drop accelerates down at 9.8 m/s2, scientists say the rock is in a
“1 g” environment, [1 g = 9.8 m/s2 = 22 mph/s].
Any time an object experiences the pull equal to the force of gravity, it is
said to be in a “one g” environment. We live in a 1 g environment. If a
rock whose weight on the Earth is 100 lbs was moved to a 2 g environment
then it would weigh 200 lbs. In a 9 g environment it would weigh 900 lbs. In
a “NEGATIVE 2 g” environment it would take 200 lbs to hold the rock down
on the ground. In a “-5 g” environment it would take 500 lbs to hold the
rock down to the ground. If the rock were put into a “zero g” environment
then it would be weightless. However, no matter what happens to its
weight the rock’s mass would never change. Mass measurement is
unaffected by the pull of gravity.
What does it feel like to walk in a 2 g environment? Find someone who’s
mass is about equal to yours. Have them give you a piggyback ride. As
you walk around this is what it feels like to be in a 2 g environment. Go
outside on the soft ground and step up on something squishy. This is when
you will really know what a 2 g environment feels like.
Often engineers will use g’s as a “force factor” unit. The force factor gives
a person a way of comparing what forces feel like.
All acceleration can be converted to g’s by dividing the answer, in m/s2,
by 9.8 m/s2.
Example
A roller coaster is propelled horizontally by a motor. The mass of the
coaster train is 8152 kg. The train starts from rest and reaches a velocity of
26.1 m/s, 55 mph, in 3.00 seconds. The train experiences a constant
acceleration. What is the coaster train’s acceleration in g’s?
Solution
m = 8152 kg
vo = 0 (starts from rest)
vf = 26.1 m/s
t = 3.00 s
a=?
vf = vo + at
26.1 = 0 + a(3.00)
a = 8.70 m/s
in g’s... 8.70 m/s2 / 9.80 m/s2 = 0.89 g’s
This means the rider is being pushed back into his seat by 89% of his
weight.
Physiological Effects of Acceleration
Imagine a passenger riding through a loop on a roller coaster. The
passenger’s head is towards the inside of the circle.
Her feet are to the outside of the circle. In order to keep blood in the
passenger’s head, a centripetal force needs to be applied to the blood
to push it upwards toward the head and the center of the circle. The
heart applies the centripetal force on the blood. A passenger can
experience many g’s in a loop. Recall that a g is the number of times
heavier an object becomes. A 7 g experience means that the passenger
feels 7 times heavier. Everything about the passenger becomes 7 times
heavier. Her 3 pound brain now weighs 21 pounds. Every ounce of blood
becomes 7 times heavier. If the blood feels too heavy the heart cannot
apply enough force to push it towards the head. If the brain does not get
any blood it will not get the oxygen the blood carries. The passenger will
pass out within a second.