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Knowing how objects should be moving in a given situation can go a long way towards helping us create believable dynamic simulations. This would mean having at least a basic grasp of the three laws of motion as set down by Sir Isaac Newton. According to Newton's first law, an object at rest will remain at rest unless acted on by an unbalanced or stronger force. By the same criteria, an object in motion continues in motion with the same speed and in the same direction unless, again, it is acted upon by an unbalanced force.
This law, often cited alongside Galileo's concepts of inertia, reminds us that there is a natural tendency of objects to keep on doing what they are doing. All objects exhibit natural resistance to changes in their current state. This means in our simulations we will need to think in terms of forces, forces to start an object moving and then forces that will act upon it to either alter its cause or behavior or maybe even to slow it down, and eventually to bring it to a stop.
According to Newton's second law, acceleration is produced when an unbalanced force acts on a mass. The greater the mass of the object being accelerated, the greater the amount of force needed to accelerate it. This of course means that everyone is unconsciously aware of Newton's second law. Everyone knows that a heavier object will require more force to move as compared to a lighter one. Rather than being expressed simply as an idea or concept, this second law can provide us with an exact relationship between force, mass, and acceleration.
In other words, it can be expressed as a mathematical equation: F=M x A. Or in English, force equals mass times acceleration. Here is an example of how Newton's second law might work. Little Johnny's bicycle has a mass of 10 kg, but it has a flat tire, so he has to push it at home. The bike is pushed at 0.1 m/s2. By using Newton's second law, we can compute how much force Johnny is applying to his bicycle.
F=10x0.1 m/sec2 would give us an answer of 1 Newton, or a force of 1 Newton being applied to move the bicycle along. According to Newton's third law, for every action, there is an equal and opposite reaction. This means that for every force, there receives a reactionary force that is equal in size but opposite in direction. The simple push or press-up as used in physical exercise can nicely demonstrate this law for us.
The action of the upper body muscles would be to push down on the ground with a particular amount of force. The reaction is that the ground would push the body upwards with an equal force, action and then equal and opposite reaction. Now, we of course won't need to become renowned physicists in order to work with simulation tools such as MassFX, but it does become very clear that the more we understand the workings of the world around us, the more we understand why objects behave as they do, the better position we will be in to produce believable, high-quality simulations.
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