# Can anyone verify if this logic has truth

1. Nov 5, 2007

### johnhaley

Can anyone verify if this logic has truth!!!

1. The problem statement, all variables and given/known data

My friend and I were having a chat about a friend that got injured on a water slide. He started to explain the physics of her body and its movement on a water slide and not being a physicist I want to see if someone can verify his logic. Heres the way i recall his explanation... all name and locations are change to protect identities :)

Me: Now when you were talking about forces of gravity and speeds on a water slide, you don't really know what the force of gravity was on jessica on the particular slides at waterland, right?

My Friend: Well, we know it's 32 feet per second per second your acceleration, and your forces, mass times acceleration. So its your body weight times your acceleration. I'm not a great physicist, but it can be figure out pretty easily by multiplying her weight in kilograms or actually her weight in pounds by 32 feet per second and your gonna get the forces. There gonna be several times body weight.

Me: But you really can't say what those are. I mean your not a physicist, right, your not--

My Friend: No I'm not a physicist, but the numbers are easy to figure, by even a lay person whos taken basic physics. It's mass, her body weight, times acceleration, 32 feet per second per second. you only need to know how many second she was on the slide. You know what her weight is and the 32 feet is constant. You don't need to be a physicist to figure out the force.

Me: But speed is a factor, right?

My Friend: speed is 32 feet per second per second gravity.

Me: that's in a free fall, in a vacuum right?

My Friend: Believe it or not you actually go faster when you have water underneath you in a water slide then 32 feet per second per second. So we know the minimum amount of force with her.

DOES ANY OF THIS MAKE SENSE. CAN SOMEONE TELL ME WHAT IS VALID AND WHAT IS NOT. YOUR HELP IS APPRECIATED

2. Nov 5, 2007

### Staff: Mentor

The friend is incorrect and terminology is incorrect.

The acceleration, g, at sealevel due to gravity is 32.2 ft/s2 or 9.81 m/s2, and this is the acceleration an object would experience in freefall.

The weigth of an object is equal to its mass (that property of matter which resists acceleration, or change in velocity) and the acceleration.

On a water slide, one certainly does not exceed the acceleration of gravity due to the resistance of the water and the fact that one is not falling vertically in free fall, and the acceleration a is given by g sin$\theta$, where $\theta$ is the angle of the incline with respect to horizontal.

http://hyperphysics.phy-astr.gsu.edu/hbase/mincl.html#c3

The water reduces the friction with the slide, but does not eliminate it.

http://hyperphysics.phy-astr.gsu.edu/hbase/mincl.html#c2