- Good morning.
I have two different equations which I use to determine the number of g’s, or what are also called g-Forces,
which act on an object, they are...
Flipping Physics
Vertical number of g's equals the force normal acting on the object
divided by the weight or force of gravity acting on the object when the object is on the surface of planet Earth.
The horizontal number of g's equals the acceleration in the x-direction of the object divided by the acceleration
due to gravity here on planet earth.
Remind me class, what is the acceleration due to gravity here on planet earth?
[Class]: Positive 9.81 meters per second squared.
- That is correct. Okay, number of g's is also sometimes called g-forces, however,
I will not refer to number of g's as g-forces very often because number of g's is not a force
and calling it g-forces will lead you to believe number of g's is a force, but number of g's is NOT a force.
Billy, please calculate the number of g’s you are currently experiencing.
- Calculate how many g’s I am experiencing right now?
- Yes, right now.
- Uh, vertical or horizontal?
- Both of them, please.
- Okay. Horizontal g’s equals my acceleration in the x- direction divided by the acceleration due to gravity.
My acceleration in the x-direction is zero, so my horizontal number of g’s is zero.
Vertical g’s is my force normal divided by my force of gravity.
We can substitute in mass times acceleration due to gravity for the force of gravity,
but I don’t know my mass, so I cannot solve for my vertical number of g’s.
- But if we draw a free body diagram of the forces acting on you right now,
we get force normal up and force of gravity down.
The net force in the y-direction then equals force normal minus force of gravity
which equals mass times acceleration in the y-direction.
Your current acceleration in the y-direction is zero,
so your force normal equals your force of gravity.
Substitute that into the equation for vertical number of g’s, everything cancels out,
and you get 1. Your vertical number of g’s is 1.
- Okay, but what are the units?
- Number of g’s has no units. It works out to be newtons divided by newtons.
Newtons cancel out and you are left with no units.
- Right. Okay!
- That is correct. When you are at rest, which humans typically are,
you are experiencing zero horizontal g’s and 1 vertical g.
What about astronauts in the International Space Station?
Bo, how many g’s are they experiencing?
- Well they will be experiencing zero horizontal g’s, just like we are.
For vertical number of g’s,
we already calculated the acceleration due to gravity in the International Space Station last time
to be roughly 8.6 meters per second squared.
So divide that by 9.81 meters per second squared to get 0.87666 or 0.88 vertical g’s.
- What are you doing?
That's not how you calculate vertical g's.
Vertical g’s are Force Normal divided by Force of Gravity.
Astronauts in the International Space Station appear to be floating and therefore have zero force normal,
so they are experiencing zero vertical g’s.
- So when you are in an orbiting space station, you experience zero g’s in every direction.
That’s exactly what we were talking about last time.
That is apparent weightlessness!
When something is experiencing zero g’s, they appear to be weightless,
even though a force of gravity is acting on them.
- Right!
Astronauts experience zero net g’s and therefore appear to be weightless.
Sounds like fun.
- Again, that is correct. But realize,
you don’t need to go into space to experience apparent weightlessness or zero total number of g’s.
You can feel zero net g's in an airplane, on a roller coaster, or even in a car.
We actually already did an example where we determined what it would take to
experience apparent weightlessness in a car.
Does anybody remember?
- That would be when we determined the maximum linear velocity to drive a car over a hill
and have the tires not to leave the ground.
When we did that problem, the critical point was
where the force normal was equal to zero.
In other words, the speed we determined is also the speed to drive the car such that
the passengers would experience apparent weightlessness
or where they would feel weightless while going over the hill.
- That means if you're riding in an airplane which is moving along a similar path
like the car going over the hill,
you can find a speed and radius to fly the plane at such that you would experience zero net g's in the airplane.
Oh, and that's kind of like what you feel when you're going over a hill on a roller-coaster. I love that feeling!
- Me too!
- You know, we have to talk about the falling bucket of water and me falling in a falling elevator again, right?
- Yes, you are correct. We absolutely have to.
- Oh that's right. You dropped the bucket of water and the water stopped flowing out of the holes
the bucket and water experienced apparent weightlessness.
- And we talked about me falling freely with and in an elevator
and how I would appear to float because I would be experiencing apparent weightlessness.
- Yeah, those are examples of objects experiencing zero net g's
Apparent weightlessness is when an object has zero net g's.
- The falling bucket and water experience zero net g's and apparent weightlessness
- If I were falling in a falling elevator I would have zero g’s and feel as if I were weightless.
- You know, that all may be true, however, I am still not really sure what number of g’s is.
- Yeah. Okay. So,
we live in a world where there is always a vertical acceleration due to gravity
of 9.81 meters per second squared, right?
[Class]: Sure, right, yes.
- So number of G's is a ratio of the acceleration experienced by the object
with respect to the acceleration
we typically experience here on planet earth.
If you are experiencing two vertical g's, you feel like you weigh twice what you normally do.
if you are experiencing 1 and a half horizontal g’s,
you feel like you have a horizontal weight
which is one and a half times your normal vertical weight
and realize you don't normally experience weight horizontally.
So, number of g's gives us a way of
comparing the acceleration an object is experiencing to what the object would normally experience
when at rest here on planet Earth.
[Class]: Okay. Yeah, okay, got it. That's logical.
- Some examples of number’s of g’s which I am not going to walk through the math for are
my 2011 Toyota Prius which can go from 0 to 35 miles per hour and 5.43 seconds.
That works out to be roughly 0.29 horizontal g’s.
Which is as many horizontal g’s my little Prius could manage.
The new Tesla Roadster which is supposed to come out in 2020
is reported to go from zero to 60 miles per hour in 1.9 seconds.
That is about 1.4 horizontal g’s.
Which will be downright amazing for a production vehicle.
Astronauts in NASA’s space shuttle experienced roughly 3 g’s during launch and the Russian Soyuz rocket,
which we currently have to use in order to get humans to the International Space Station,
experiences roughly 4 g’s during launch.
Those are some real life examples of numbers of g’s.
Thank you very much for learning with me today.
I enjoyed learning with you.