MECH 222 Dynamics of Rigid Bodies ASSIGNMENT NO.1 1. What is Dynamics? Dynamics is the branch of mechanics that deals with the study of bodies in motion. Dynamics has its origins in the Greek word dynamis, "force, power." In physics, dynamics is the study of bodies in motion and changes in that motion, and that idea can be applied to other areas as well. For example, we refer to "group dynamics" as the way people interact and work together. George W. Bush once observed, "Globalization has altered the dynamics in the White House, as well as between the White House and the Treasury." 2. What is the difference between Kinematics and Kinetics? Kinematics is the geometry of motion. The term is used to define the motion of a particle or body without consideration of the forces causing the motion. Kinematics is essentially a treatment of the relations between displacement, velocity, and acceleration. While Kinetics is the branch of dynamics that relates the force acting on a body to its mass and acceleration. When the acceleration of a body caused by the forces acting on it has been determined, the principle of kinematics may be applied to determine the displacement or velocity at any instant. In other cases, the kinematic motion of a body may be used to compute its acceleration; from this, by means of the relations to be developed later, the force or forces required to produce this motion can be determined. 3. Enumerate and explain Newton’s Law of Motion of a Particle? Site an example for each. Newton’s laws of motion for a particle have been stated in a variety of ways. For purposes we shall phrase them as follows: 1. A particle acted upon by a balanced force system has no acceleration. When all the forces acting upon an object balance each other, the object will be at equilibrium; it will not accelerate. For example, consider a physics book at rest on a tabletop. There are two forces acting upon the book. One force, the Earth's gravitational pull exerts a downward force. The other force, the push of the table on the book (sometimes referred to as a normal force) pushes upward on the book. Since these two forces are of equal magnitude and in opposite directions, they balance each other. The book is said to be at equilibrium. There is no unbalanced force acting upon the book and thus the book maintains its state of motion. 2. A particle acted upon by an unbalanced force system has an acceleration in line with and directly proportional to the resultant of the force system. This means that the presence of an unbalanced force will accelerate a particle changing its speed, its direction, or both its speed and direction. Consider that the car is accelerating to the right. Therefore, the net force is to the right since the acceleration is to the right. An object which moves to the right and speeds up has a rightward acceleration. 3. Action and reaction forces between two particles are always equal and oppositely directed. This means that when two particles collide, both particles experience forces that are equal in magnitude and opposite in direction. Such forces often cause one particle to speed up (gain momentum) and the other particle to slow down (lose momentum). Consider the collision between a moving seven ball and an eight ball that is at rest in the sport of table pool. When the seven ball collides with the eight ball, each ball experiences an equal force directed in opposite directions. The rightward moving seven ball experiences a leftward force that causes it to slow. down; the eight ball experiences a rightward force that causes it to speed up. Since the two balls have equal masses, they will also experience equal accelerations. In a collision, there is a force on both objects that causes an acceleration of both objects; the forces are equal in magnitude and opposite in direction. For collisions between equal-mass objects, each object experiences the same acceleration.
