Game Physics

S0m30n3 said:
I dont think you knnow what your talking about. Atleast show me some resources so I can understand and learn.
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I know precisely what Im talking about. You quoted an incorrect web site to attempt to make an incorrect answer to a simple question. You gave the wrong answer that makes other people think its correct. People need basic fundementals, not misinformation. They simply are to arrogant or lazy to look them up in a textbook and resort to misinformation posted on some website. Im not trying to flame anybody or be a jerk (although now that I think about it maybe i am??? and i apologize.) but I just wish we cuuld discuss basic principles without resorting to some web posting contest. :D
 
truffle00 said:
..snip...
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I entirely agree, its all a question of marketing, if HL2 had shipped without the physics model it did (you can never completly remove it, but say if it was like Quake 3) then it wouldnt be half the game it was, sure some of it was cheesy, but a lot of it was hella cool, and it is an evolutionary thing, game physics has been getting gradually better, its less obvious than graphics, so it isnt were all the money gets spent.
 
So your saying if you release a 100lb and a 50lb ball same shape and size in water(a force greater than air). Because they are the same shape and size they will sink at the same speed just 1 will gain more momentum and momentum wont have an effect on the force of water trying to stop it. The lighter object which isnt going as fast will have less resistance and fall quicker?
 
S0m30n3 said:
So your saying if you release a 100lb and a 50lb ball same shape and size in water. Because they are the same shape and size they will sink at the same speed just 1 will gain more momentum and momentum wont have an effect on the force of water trying to stop it. The lighter object which isnt going as fast will have less resistance and fall quicker?
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Again, youre confusing momentum and speed, but yes, if they are the same shape + size then they will fall at the same speed. Drag is a function of shape, and has nothing to do with how massive something is.
 
Wrench00 said:
Is it just me or am I the only person NOT impressed by any of these fancy or supposed fancy physics. The Aegia PPU sure looks like a great thing but the physics just seem so unrealistic in every game I have played. HL2, D3, BF2, etc. They all seem like the location is somewhere under water, stuff falls down really slow, and it looks like it has absolutly no substance to the items. It just seems like everything in games is made out of paper. Then there is rag doll physics well let me tell you that human leg doesn't bend 180 degrees. Common can we at least pay attention kinematics a little. Oh and can I comment on the fact that when you shoot some one in the head with a 5.56 nato round their body doesn't go flying 6 feet back ( I shot a lot of guns and not single round ever made anything fly back that had any weight to it).
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I was reasonably impressed by the HL2 physics model. I recall in HL1 in the air-tram scene, if you jumped, then you would FLY backwards in the tram, indicating that the game had not translated the speed you had gained from moving in the train, whereas this was not true in the opening train scene in HL2.

I've never shot anyone in the head with a gun, but say you shot someone up close, and the bullet did penetrate, but did not exit, its full translational momentum would be put into the head. Feasibly, since bullets move quick quickly, it would translate into a jerking of the head, which could feasibly lead to movement of the entire body.

ie, in this case, where v1m1 = bullet momentum, and v2m2 = person momentum, and

v1 = big, and m1 = small, and v2=0 and m2 = big (therefore p2 = 0), then when there is impact, v1m1 = m(1+2)*VELOCITY OF NEW SYSTEM.
 
Two objects, no matter what the difference in weight, will hit the ground at the very same time, in a vacuum.

Objects will hit the ground at different speeds, when not in a vacuum, because there are other forces present such as air, water resistance, buoyancy. I say again there are additional forces applied to objects when not in a controlled environment such as a vacuum.

As for the water example buoyancy comes into play at this point.
 
Herulach said:
Again, youre confusing momentum and speed, but yes, if they are the same shape + size then they will fall at the same speed. Drag is a function of shape, and has nothing to do with how massive something is.
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Momentum: A measure of the motion of a body equal to the product of its mass and velocity.

Velocity: Physics. A vector quantity whose magnitude is a body's speed and whose direction is the body's direction of motion.

Is dictionary.com wrong or am I miss interpreting the definition?
 
S0m30n3 said:
Momentum: A measure of the motion of a body equal to the product of its mass and velocity.

Velocity: Physics. A vector quantity whose magnitude is a body's speed and whose direction is the body's direction of motion.

Is dictionary.com wrong or am I miss interpreting the definition?
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The definition isn't wrong, but you certainly could be missing the concepts.

1 will gain more momentum and momentum wont have an effect on the force of water trying to stop it.
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Momentum stays the same unless outside forces act on an object. In this case GRAVITY acts on both objects at the same time - so their momentum changes at the same rate.
 
S0m30n3 said:
Momentum: A measure of the motion of a body equal to the product of its mass and velocity.

Velocity: Physics. A vector quantity whose magnitude is a body's speed and whose direction is the body's direction of motion.

Is dictionary.com wrong or am I miss interpreting the definition?
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meh
 
If I took two cartons of milk 1 filled 1 empty and dropped them high enough to catch wind resistance because they are the same shape and form the weight of the one filled with water wont effect the force the air has on it?
 
ryanrule said:
momentum is a measurement of energy. say a roller coaster, at the top of the hill you have lots of potential energy, but little kinetic energy (momentum, or the energy of movement). at the bottom you have tons of kinetic energy but little potential energy.
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false - while momentum and energy are related, they are not measurements of eachother e.g. momentum units = kg*m/s^2 whereas energy is Kg*m^2/s^2 or (J)
 
S0m30n3 said:
If I took two cartons of milk 1 filled 1 empty and dropped them high enough to catch wind resistance because they are the same shape and form the weight of the one filled with water wont effect the force the air has on it?
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yup
 
aranaxon said:
false - while momentum and energy are related, they are not measurements of eachother e.g. momentum units = kg*m/s^2 whereas energy is Kg*m^2/s^2 or (J)
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yeah i was thinkin mv^2

edit: come to think of it, isnt momentum just a concept set up to make collisions easier?
 
pretty much

i'm not sure what its derived from.. but w/ energy concepts, it makes mapping collisions in "physics ideal environments" easier =)
 
I dont understand it. It doesnt make sense. Weight would be transfered into a form of energy. The energy would be used to counter act the resistance of air.
 
S0m30n3 said:
If I took two cartons of milk 1 filled 1 empty and dropped them high enough to catch wind resistance because they are the same shape and form the weight of the one filled with water wont effect the force the air has on it?
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You ever take physics in HS or University??? There are a hell of alot of mathematical formulas that apply to this situation. But elementally, two objects regardless of anything else will fall at the same RATE unless acted on by other FORCES. Again this is elemental physics not real world testing. The real world is not perfect,elemental physics is.
 
What about parachutes. They use wind resistance. If I was to strap the same size boxes on the same size parachutes everything identicle except one weighed 90tons would they fall at the same speed?
 
S0m30n3 said:
I dont understand it. It doesnt make sense. Weight would be transfered into a form of energy. The energy would be used to counter act the resistance of air.
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Have you had a physics class yet? You seem to be having a hard time grasping the principles of what physics actually is. Energy is neither created or destroyed. You can't get free energy. Countering air resistance would require an opposing force. In other words, throwing a baseball harder (force from your arm / faster muscle contraction), or adding more gun powder to a gun to force the bullet out faster. Weight is just a function of the gravitational force, which is why we would weigh less on the moon than on earth. Just keep in mind, whenever you are talking about something doing any kind of work (countering air resistance ^^) energy is required. Making something bigger doesn't add energy. It's still being acted on by the same force as it was before, unless you are somehow change that force.
 
S0m30n3 said:
I dont understand it. It doesnt make sense. Weight would be transfered into a form of energy. The energy would be used to counter act the resistance of air.
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Weight is a measurement of the force exerted my gravity. Force = mass x acceleration. This is the big equation that runs almost all of classical physics. Mass is a measurement of the amount of material in a specific object. Mass is constant, weight isnt. Your mass is the same on earth as it is on the moon, but your weight is less on the moon.

The resistance of the air is determined by the area that the air resistense is acting on and the speed of the object. There are other factors but they are negligable for this arguement. The air resistance creates a force opposing the gravitational force. This may be the energy you are thinking of, though it is not energy at all.
 
Velocity = Acceleration * Time Traveled up until terminal velocity, something determined by drag characteristics, what the object is moving through etc.

Terminal velocity is the point at which the force exerted by the medium upon the object is equal to the force accelerating it.

However, two things, with all attributes the same bar. weight, will have the same velocity relative to time.
 
WOW!

didnt think my post would create the monster that has become this thread

im not a physics major...... shit i barely attended HS science class, but i was under the impression that everyone at one point or another figured this out or tried it or something


drop a watermelon and a penny from the roof and they hit at the same time

all the momentum and velocity and stuff doesnt even apply, just wind resistance

anyways the point is, the person i was posting at was scoffing at the physics because he "threw heavy stuff and it all came down the same"
 
Yeah I understand how they would hit at the same time from a rooftop. But when theres wind resistance from higher speeds at higher sitances slowing things down I would think the heavier object would end up going faster because it would take more resistance to slow it down.
 
S0m30n3 said:
Yeah I understand how they would hit at the same time from a rooftop. But when theres wind resistance from higher speeds slowing things down I would think the heavier object would have an easier time because it would take more resistance to slow it down.
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that kind of wind resistense in not worth considering unless you are going quite fast.
 
What 10mph? Take an empty gallon of milk and one filled with water. Get a fan to blow air at them. Which one can resist the force of the air better? Hell I'll even record a short video of what happens.
 
S0m30n3 said:
What 10mph? Take an empty gallon of milk and one filled with water. Get a fan to blow air at them. Which one can resist the force of the air better? Hell I'll even record a short video of what happens.
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or when an object is excessively light that the gravitational force is near the frictional force. but i though we were talking about crates and human bodies?
 
Give them wheels and have one filled half way or 3\4. Which one will resist more?
 
S0m30n3, are you trolling here? Seriously, you post every five seconds and now you have a really bizarre question about putting a gallon of milk and a gallon of water on wheels with fans blowing on them asking about resistance. If you're really serious about knowing this stuff, I'd stop posting and making yourself look like Michael Jackson at a daycare and just spend an hour over at Wikipedia reading up on basic Physics 101. Seriously, it sounds like you love to post to hear yourself talk or love arguing, both are not redeeming qualities.

Until you understand the very simple concepts of mass, force and resistance, it's not worth answering your questions because you won't understand the answers. No one here has the time to teach you something you learn as a high school freshman.
 
Well after reading the net from various sources the only way something is going to fall at the same speed is if the only force is gravity. The link I provided with my first post says it all and so do,
http://electron9.phys.utk.edu/phys135d/modules/m2/Freefall.htm
http://www-istp.gsfc.nasa.gov/stargaze/Lfall.htm
http://www.physicsclassroom.com/mmedia/newtlaws/efar.html
http://www.glenbrook.k12.il.us/gbssci/phys/Class/newtlaws/u2l3e.html
http://galileo.rice.edu/sci/theories/on_motion.html

Im not sure how the debate started but lets end it here.
 
Herulach said:
You had to go to a website that was wrong too? Weight has no effect on air resistance. Make a golfball out of lead and put it next to a real golfball, then drop it out of a plane, both will stilll hit the floor at the same time (assuming same winds for both etc)
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O wait here it is.
 
I think that HL2 took a great leap forward in the physics department. Physics are something I'm really looking forward to in games. I can't wait for the day that we can shoot a corner of a building and have it fall apart, not just a little bullet image pasted on the wall.
 
On a small scale there'll indeed be very little difference between the terminal velocities of two similarly shaped objects with each a different mass.

In a gas (air) or in a fluid, there'll be a limit to how fast an object can fall due to friction. In a (perfect) vacuum, however, there's no such limit.

http://en.wikipedia.org/wiki/Potential_energy#Gravitational_potential_energy

Recall the gravitational potential energy formula: Ug = mgh

Assuming g and h are constant, then in- or decreasing m will increase, respectively decrease the amount of potential energy.
When an object is released from height h, all this potential energy will have been converted to kinetic energy by the time it reaches h0.

Ergo, heavier objects will fall faster when the conditions are right :)
 
bobsaget said:
I think that HL2 took a great leap forward in the physics department.
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And just how long has Havok been around :rolleyes:
 
You're discussing free fall but not one differential equation has been brought up yet?
 
Wrench00 said:
Is it just me or am I the only person NOT impressed by any of these fancy or supposed fancy physics. The Aegia PPU sure looks like a great thing but the physics just seem so unrealistic in every game I have played. HL2, D3, BF2, etc. They all seem like the location is somewhere under water, stuff falls down really slow, and it looks like it has absolutly no substance to the items. It just seems like everything in games is made out of paper. Then there is rag doll physics well let me tell you that human leg doesn't bend 180 degrees. Common can we at least pay attention kinematics a little. Oh and can I comment on the fact that when you shoot some one in the head with a 5.56 nato round their body doesn't go flying 6 feet back ( I shot a lot of guns and not single round ever made anything fly back that had any weight to it). Its fun to see a guy get thrown in the air 20 feet on an explosion but I would have given my right gonad to see his gibs go flying in 20 different directions. Aegia PPU is great at speeding up and adding complexity to scripted physics but why would you want to have 10000 things that look like and feel like they are made out of paper. (Ohhh NOES the 10000 paper tissues will crush me)

Developers can you please spend some time on AI instead?
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THey havnt been given

A) Enough time to develop the physics to look real

B) The power to make the things look real (hence the PPU)

Numbnuts
 
Sly said:
And just how long has Havok been around :rolleyes:
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I have no idea.


But it is just that it has better physics than a lot of games. For example... BF2's physics absolutely suck.
 
bobsaget said:
I have no idea.


But it is just that it has better physics than a lot of games. For example... BF2's physics absolutely suck.
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But do physics add anything to BF2's gameplay? No. I'd rather have bodies that just dissapear when they are killed and better lighting effects than some stupid ragdoll animation that you don't pay attention to. Physics (at this point) really lends itself more towards single player games at the moment. I'd rather not have uber leet physics that will dictate how a gun should fall when someone is killed but instead be able to add an extra 12+ players to the max number of players on a given server using the same CPU utilization.
 
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