kidzsearch.com > wiki
Classical mechanics
Mechanics is a part of physics. It says what happens when forces act on things. There are two parts of mechanics. The two parts are classical mechanics and quantum mechanics. Classical mechanics is used most of the time, for most of the things we can see. Some of the time, for example when the things are too small, classical mechanics is not good. Then we need to use quantum mechanics.
Contents
Newton's Three Laws
Newton's three laws of motion are important to classical mechanics. Isaac Newton made them.
The first law says that, if there is no external force (meaning there is no pushing, gravity, or any sort of power), things that are stopped will stay stopped or unmoving, and things that are moving will keep moving. Before, people thought that things stopped if there was no force present. Often, people say, Objects that are stopped tend to stay stopped, and objects that are moving tend to stay moving, unless acted upon by an outside force, such as gravity, friction, etc....
The second law says how a force moves a thing. The force on an object equals the rate of change of the velocity.
The third law says that if one thing puts a force on another thing, the second thing also puts a force on the first thing. For example, if you jump forward off a boat, the boat moves backward. Often, people say, For every action there is an equal and opposite reaction.
Kinematic Equations
In physics, kinematics is the part of classical mechanics that explains the movement of objects without looking at what causes the movement or what the movement affects.
1Dimensional Kinematics
1Dimensional (1D) Kinematics are used only when an object moves in one direction: either side to side (left to right) or up and down. There are equations with can be used to solve problems that have movement in only 1 dimension or direction. These equations come from the definitions of velocity, acceleration and distance.
 The first 1D kinematic equation deals with acceleration and velocity. If acceleration and velocity do not change. (Does not need include distance)
 Equation: [math]V_f=v_i+at[/math]
 V_{f} is the final velocity.
 v_{i} is the starting or initial velocity
 a is the acceleration
 t is time  how long the object was accelerated for.
 Equation: [math]V_f=v_i+at[/math]
 The second 1D kinematic equation finds the distance moved, by using the average velocity and the time. (Does not need include acceleration)
 Equation: [math]x=((V_f+V_i)/2)t[/math]
 x is the distance moved.
 V_{f} is the final velocity.
 v_{i} is the starting or initial velocity
 t is time
 Equation: [math]x=((V_f+V_i)/2)t[/math]
 The third 1D kinematic equation finds the distance travelled, while the object is accelerating. It deals with velocity, acceleration, time and distance. (Does not need include final velocity)
 Equation: [math]X_f=x_i+v_it+(1/2)at^2[/math]
 [math]X_f[/math] is the final distance moved
 x_{i} is the starting or initial distance
 v_{i} is the starting or initial velocity
 a is the acceleration
 t is time
 Equation: [math]X_f=x_i+v_it+(1/2)at^2[/math]
 The fourth 1D kinematic equation finds the final velocity by using the initial velocity, acceleration and distance travelled. (Does not need include time)
 Equation: [math]V_f^2=v_i^2+2ax[/math]
 V_{f} is the final velocity
 v_{i} is the starting or initial velocity
 a is the acceleration
 x is the distance moved
 Equation: [math]V_f^2=v_i^2+2ax[/math]
2Dimensional Kinematics
2Dimensional kinematics is used when motion happens in both the xdirection (left to right) and the ydirection (up and down). There are also equations for this type of kinematics. However, there are different equations for the xdirection and different equations for the ydirection. Galileo proved that the velocity in the xdirection does not change through the whole run. However, the ydirection is affected by the force of gravity, so the yvelocity does change during the run.
XDirection Equations
 Left and Right movement
 The first xdirection equation is the only one that is needed to solve problems, because the velocity in the xdirection stays the same.
 Equation: [math]X=V_x*t[/math]
 X is the distance moved in the xdirection
 V_{x} is the velocity in the xdirection
 t is time
 Equation: [math]X=V_x*t[/math]
YDirection Equations
 Up and Down movement. Affected by gravity or other external acceleration
 The first ydirection equation is almost the same as the first 1Dimensional kinematic equation except it deals with the changing yvelocity. It deals with a freely falling body while its being affected by gravity. (Distance is not needed)
 Equation: [math]V_fy=v_iygt[/math]
 V_{fy} is the final yvelocity
 v_{iy} is the starting or initial yvelocity
 g is the acceleration because of gravity which is 9.8 [math]m/s^2[/math] or 32 [math]ft/s^2[/math]
 t is time
 Equation: [math]V_fy=v_iygt[/math]
 The second ydirection equation is used when the object is being affected by a separate acceleration, not by gravity. In this case, the ycomponent of the acceleration vector is needed. (Distance is not needed)
 Equation: [math]V_fy=v_iy+a_yt[/math]
 V_{fy} is the final yvelocity
 v_{iy} is the starting or initial yvelocity
 a_{y} is the ycomponent of the acceleration vector
 t is the time
 Equation: [math]V_fy=v_iy+a_yt[/math]
 The third ydirection equation finds the distance moved in the ydirection by using the average yvelocity and the time. (Does not need acceleration of gravity or external acceration)
 Equation: [math]X_y=((V_fy+V_iy)/2)t[/math]
 X_{y} is the distance moved in the ydirection
 V_{fy} is the final yvelocity
 v_{iy} is the starting or initial yvelocity
 t is the time
 Equation: [math]X_y=((V_fy+V_iy)/2)t[/math]
 The fourth ydirection equation deals with the distance moved in the ydirection while being affected by gravity. (Does not need final yvelocity)
 Equation: [math]X_fy=X_iy+v_iy(1/2)gt^2[/math]
 [math]X_fy[/math] is the final distance moved in the ydirection
 x_{iy} is the starting or initial distance in the ydirection
 v_{iy} is the starting or initial velocity in the ydirection
 g is the acceleration of gravity which is 9.8 [math]m/s^2[/math] or 32 [math]ft/s^2[/math]
 t is time
 Equation: [math]X_fy=X_iy+v_iy(1/2)gt^2[/math]
 The fifth ydirection equation deals with the distance moved in the ydirection while being affected by a different acceleration other than gravity. (Does not need final yvelocity)
 Equation: [math]X_fy=X_iy+v_iy+(1/2)a_yt^2[/math]
 [math]X_fy[/math] is the final distance moved in the ydirection
 x_{iy} is the starting or initial distance in the ydirection
 v_{iy} is the starting or initial velocity in the ydirection
 a_{y} is the ycomponent of the acceleration vector
 t is time
 Equation: [math]X_fy=X_iy+v_iy+(1/2)a_yt^2[/math]
 The sixth ydirection equation finds the final yvelocity while it is being affected by gravity over a certain distance. (Does not need time)
 Equation: [math]V_fy^2=V_iy^22gx_y[/math]
 V_{fy} is the final velocity in the ydirection
 V_{iy} is the starting or initial velocity in the ydirection
 g is the acceleration of gravity which is 9.8 [math]m/s^2[/math] or 32 [math]ft/s^2[/math]
 x_{y} is the total distance moved in the ydirection
 Equation: [math]V_fy^2=V_iy^22gx_y[/math]
 The seventh ydirection equation finds the final yvelocity while it is being affected by an acceleration other than gravity over a certain distance. (Does not need time)
 Equation: [math]V_fy^2=V_iy^2+2a_yx_y[/math]
 V_{fy} is the final velocity in the ydirection
 V_{iy} is the starting or initial velocity in the ydirection
 a_{y} is the ycomponent of the acceleration vector
 x_{y} is the total distance moved in the ydirection
 Equation: [math]V_fy^2=V_iy^2+2a_yx_y[/math]
Related pages
Other websites
 Science aid: Newton's laws of motion
 The Engineering Wiki's shorter page: Newton's laws of motion  engineers may improve it!
 Newtonian Physics  an online textbook
 Trajectory Video  video clip showing exchange of momentum
 Newtonian attraction for three Planets (Mathcad Application Server)
 Gravity  Newton's Law for Kids
 On Line Study Guidestudy guide for high school students

