Classical Mechanics is the study of bodies in motion. Most of this study is built on work done by Isaac Newton.
- Newton’s first law of motion
- Newton’s second law of motion
- Newton’s Third law of motion
- Newton’s Law of Universal Gravitation
- Conservation of Energy
- Conservation of Momentum
- Bernoulli’s Principle
Newton’s First Law carries the idea that a body in motion tends to stay in motion a body at rest tends to stay at rest. Twist your mind just a little bit and tell yourself that v=o is a velocity. This law hold true in the absence of a cause for acceleration, which brings us to the next law…
Newton’s Second Law relates Force and Acceleration. Acceleration may be caused by a gravitational attraction between two bodies (such as a planet and a spaceship). Acceleration may also be caused when an engine fires a stream of exhaust in the direction opposite to the desired direction of travel. The idea here is found in the overlap between this law (the second law) and the third which is introduced in the next topic and also the idea after that, Newton’s Law of Universal Gravitation.
The idea of Force comes into play when something else puts a force on an object, and the calculation to determine the acceleration requires that we know the mass of the object–more mass means less acceleration for a given Force.
Newton’s Third Law is usually stated as “for every action there is a reaction of equal magnitude in the opposite direction, and the actions and reactions are forces. Again, the idea of the the rocket exhaust moving in one direction and the rocket moving in the other.
Newton’s Law of Universal Gravitation makes use of Newton’s second law. There is a force brought about by the masses of two objects, and Force on a mass results in acceleration, which changes the velocity which otherwise would remain constant (as stated in the First Law).
Conservation of Energy carries with it the idea that we don’t get something from nothing. It also means we are ignoring Forces of Dissipation such as Surface Friction and Wind Resistance. We are better off discussing position, velocity and acceleration for an object in space, where forces of dissipation are negligible. When driving a car on a highway, pressing on the accelerator (the gas pedal) results in acceleration until the resistance force, partially wind resistance but mostly friction from the tires on the road, provides a force equal to the force caused by pressing on the accelerator, and then velocity becomes constant.
Conservation of Momentum is why it’s really bad for a person weighing 50 kg to be hit by a forklift weighing 2500 kg moving at a velocity of 20 kph. Assuming perfect transferal of momentum, that person goes flying at a velocity of 1,000 kph. That is faster than the speed of sound.
Bernoulli’s Principle relates an increase in fluid speed to a loss in either pressure or potential energy. We can think of Bernoulli’s Principle as being a specific example of Conservation of Energy.
Rob Sterling 