# 11A Describing Position

• Wandering Planets

• Mechanics: the study of motion

• Kinematics: the study of how things move

• Dynamics: the branch of physics that studies forces and how they can change an object’s motion

• History of Mechanics

• Retrograde Motion: the apparent motion of some planets in which they appear to slow down, stop, reverse their direction, and then resume their normal motion

• Quantum Mechanics: the branch of physics that explores the behavior of matter and energy at the atomic and subatomic level

• Relativistic Mechanics: the study of the motion of objects whose speeds are near the speed of light

• Frame of Reference

• Frame of reference: a coordinate system used to describe the motion of an object

• Distance and Displacement

• Distance: how far an object moves during a time interval

• Displacement: a vector quantity that describes a change in position

• Scalars and Vectors

• Scalar: a measurable quantity that consists of magnitude (size) only

• Vector: a measurable quantity with both magnitude and direction

# 11B Describing Motion

• Speed: a scalar quantity indicating the rate at which an object moves

• Velocity: a vector quantity indicating the rate at which an object’s position changes

• Momentum

• Momentum: a property of a moving system that is equal to its velocity times its mass

• Conservation of Momentum: states that within a closed system - a system that is isolated from outside. pushes or pulls - the total momentum remains constant

# 11C Changing Motion

• Acceleration: the rate of change in velocity

• Free Fall: the motion of an object that falls due to gravity alone, with no other forces acting on it

• Two-Dimensional Motion

• Circular Motion: movement along a circular path

• Centripetal Acceleration: acceleration that causes an object to move along along a circular path

• Projectile Motion: the two-dimensional motion of any flying object whose path is determined by the influence of an external force only, such as gravity

• Trajectory: the curved path of a projectile