Two major divisions of Mechanics:
- study of motion without reference to the forces causing the motion using mathematical relationships:
2. kinetics
- relates forces to motion
- relates forces to motion
Newton's Laws of Motion:
1st law:
A body in motion tends to stay in motion.
A body at rest wants to stay at rest.
ie - things want to keep doing what they are doing, you have to apply a force if you want it to change what it is doing.
Inertia = the resistance of any physical object to any change in its motion
2nd law: Force = Mass * acceleration
The acceleration of a particle is proportional to the force acting on it and inversely proportional to the particle mass; the direction of acceleration is the same as the force direction.
Large m, Large F.... small F, small m
F = ma
Constant acceleration
3rd law:
The forces of action and reaction between contacting bodies are equal in magnitude, opposite in direction, and co-linear.
Law of gravitation:
The force of attraction between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
Many STEM classes revolve around Newton's laws, and understanding how best to control and use forces.
Free-Body Diagrams
A sketch or picture of the problem
Free Body Diagram, FBD
A sketch showing the forces on point "A" in the above problem:
Free Body Diagram, FBD
A sketch showing the forces on point "A" in the above problem:
Forces are represented by arrows. Notice this arrow, or vector, has two important pieces of information:
1. The direction
2. The magnitude (length).
Rectangular Components of a Force: Unit Vectors
rectangular vector components
..
unit vectors
scalar components Fx and Fy
Common Forces:
Spring Force:
Wind drag:
