Science universe: Physics articles

Forces (including friction) In the development of mechanics, the first thing to learn is the interrelation of position, velocity, and acceleration (for constant acceleration). These interrelations are described with the four kinematic equations of motion and discussed in earlier chapters. In this chapter we relate constant force to constant acceleration and then to all of kinematics. Operationally, force can be defined as what makes masses accelerate. Actually it is the unbalanced force on a mass that makes it accelerate. Simply: Unbalanced forces make masses accelerate. Force, acceleration, and mass are related by Newton's second law as F = ma. 5 1 A 40 N force is applied to a 20kg block resting on a horizontal frictionless table. Find the acceleration? Solution: The acceleration is Fig. 5 1 Once the acceleration is known, the kinematic equations of motion can be applied to find position, velocity, and acceleration as a function of time. <>...

Projectile Motion In order to understand projectile motion you have to look at the motion in two directions with one direction oriented in the direction of constant acceleration and the other direction at a right angle to it so as to form an x y coordinate system. In most problems, where an initial velocity and angle with the horizontal is given, the velocity is written in component form. Fig.4 1 Note that the motion is effectively separated into horizontal and vertical components (one in the direction of the constant acceleration and one at a right angle to the acceleration). The motion is a parabola in this coordinate system. The symmetry of parabolas (in this case parabolic motion) is helpful in understanding the motion. (See the Introduction, Mathematical Background, for a discussion of the properties of parabolas.) In order to better understand how the motion is separated and how the parabolic property helps us to understand projectile problems we will do a simpl...