roller coasters

[cool dude]

for those of you who've been on a roller coaster you've noticed that when your going down the hill you get lifted up from your seat. now my question is why does this happen? at first i thought that the normal force was greater than gravitational force, thus pushing you out of your seat, but then i remembered that normal force can never be greater than gravitational force so thats wrong. i also thought maybe it has something to do with the speed but i'm not too sure. any ideas?

[Cervantes]

When you're going down a (straight) hill? Well, as you're going down the (straight) hill, you won't feel any different. However, as you go over the top of the hill, starting the descent, you would feel pushed out of your seat.

This is because of your inertia. You were previously climbing the hill, so you're moving somewhat upwards. Then, all of a sudden, the cars are pulled downwards along the track beneath you, so relative to the seat, your body moves up. Not for long, thankfully.

[Mazer]

Hmm... on the two roller coasters I've ridden I remember being more focused on my ability to exhale rather than my position relative to the seat. But as Minsc said, the feeling shouldn't last long, assuming you haven't strapped on a parachute.

[wtd]

Mazer wrote:

But as Minsc said, the feeling shouldn't last long, assuming you haven't strapped on a parachute.

I sense the next great amusement park attraction in the works here.

[Blade]

its like being in a car... without your seatbelt, going over a bump you'll be launched upward and hitting your head off the roof. because the car is heavier it has a stronger gravitational attraction pulling it down more quickly than you are. because the rollercoaster is heavier and is attached to the rails it changes direction more quickly than you. this is another part but inertia is also involved like cervantes said.

[1of42]

man blade, I'm pretty sure that weight of the objects really has nothing to do with it.

[cool dude]

1of42 wrote:

man blade, I'm pretty sure that weight of the objects really has nothing to do with it.

i think wat blade meant was that heavier objects have more inertia thus resist more change. anyways thanks guys for the help!

***Edit*** cerventes can u recommend any good physics books i can read. wat books did u read because i always see u knowing so much about physics.

[Cervantes]

cool dude wrote:

***Edit*** cerventes can u recommend any good physics books i can read. wat books did u read because i always see u knowing so much about physics.

A Brief History of Time by Stephen Hawking is a good book. Lots on cool stuff like black holes.

But my personal favorite: The Elegant Universe by Brian Greene. This book walks you through Special Relativity, then moves you into General Relativity. From there, it jumps to Quantum Mechanics and gives you as much of an intuitive understanding of QM as is possible. Now that the reader has learned about GR and QM, the reader can see why the two theories clash when they are used together (at extremely massive but extremely small places, like black holes). The book then begins a wild and wonderful journey through more modern physics, the attempts to resolve the conflict between GR and QM. The main focus of the book is Superstring Theory, which gives you fun things such as 11 dimensions. It goes quite deep into some of the finer details of string theory, and even outlines how theoretical physicists work on string theory (largely: perturbation theory, used to find approximate answers to approximate equations).

A fantastic read.

But if you want to learn about Newtonian physics, don't read that. What I know of Newtonian physics is from the physics courses at school. Physics textbooks are everywhere.

cool dude wrote:

i think wat blade meant was that heavier objects have more inertia thus resist more change. anyways thanks guys for the help!

Inertia is a property, not a quantity. You'd be referring to momentum, symbolized by 'p' and equal to mass times velocity. So yes, more massive objects do have more momentum. However, more massive objects have a greater force of gravity acting on them (force is linearly dependant on mass). All objects fall at the same rate, regardless of their mass. Thus, the reason the roller coaster cart drops faster than you do is because it is pulled down by the track. You, on the other hand, are pulled down only by the safety gear holding you to the seat, which doesn't fit as snugly as the cart's wheels do to the track.

[Blade]

1of42 wrote:

man blade, I'm pretty sure that weight of the objects really has nothing to do with it.

i basically said what cervantes said above, i jsut didnt describe it as well as he did.

Cervantes wrote:

All objects fall at the same rate, regardless of their mass. Thus, the reason the roller coaster cart drops faster than you do is because it is pulled down by the track.

just to add: if there were no tracks, because of the larger gravitationall pull, the rollercoaster will fall before you do.

[Cervantes]

Blade wrote:

Cervantes wrote:

All objects fall at the same rate, regardless of their mass. Thus, the reason the roller coaster cart drops faster than you do is because it is pulled down by the track.

just to add: if there were no tracks, because of the larger gravitationall pull, the rollercoaster will fall before you do.

Blade: Noooo!!
If I were sitting in a roller coaster cart moving perfectly horizontally, and the track suddenly ended at the edge of a cliff, the roller coaster cart and I would fly off the cliff and would fall at exactly the same rate. I would remain in the seat of the cart.

Mass has nothing to do with acceleration due to gravity (unless you're taking into account air resistance, which is negligable in this situation).

Let's prove this mathematically:

By Newton, the force of gravitational attriction between two masses m1 and m2 separated by a distance d equals G * m1 * m2 / d^2,

Also by Newton, (second law of motion) F = ma.

Now, in the case of free fall, the only force acting on the object is the force of gravity. Thus,
G * m1 * m2 / d^2 = ma
If m1 represents the mass of the person or roller coaster cart and so does m, they cancel, leaving us with
a = G * m2 / d^2
Therefore, acceleration due to gravity has nothing to do wit the mass of the falling object.

[1of42]

Now, that was what I was getting at, but was too lazy to take all the effort to post.

[Cervantes]

Laziness and physics were never meant to be together.

[Mazer]

Cervantes wrote:

Laziness and physics were never meant to be together.

Right, because that's why they made elevators.

[codemage]

If I dropped you and a rollercoaster from a big tower at the same time, you'd both hit the ground at the same time.

Neat experiment:
If I let you take a running outwards jump, and then dropped the rollercoaster (I'm strong) when you were at the level, you'd still make a ground dent at the same time.

The rollercoaster thing is about inertia. Your mass (and even your internal organs) don't change directions as quickly as the cart b/c you aren't nailed down.

There are some rides out there that give you the same feeling for longer periods by descending faster than or equal to the negative acceleration of gravity.

[Andy]

codemage wrote:

If I dropped you and a rollercoaster from a big tower at the same time, you'd both hit the ground at the same time.

actually they wouldnt. depending on the orientation of the object during the fall, namely the frontal area, terminal velocity is reached at different speeds.

when we're little we think heavier things fall faster, then we grow older people tell us everything falls at the same speed, and older yet we're told that heavier things indeed fall faster.