General motion: Motion is made up of a mix of angular (rotational) and linear (translational) movement. A mix of the two is called "general motion".

Speed: Speed is a scalar measure indicating how fast an object is traveling at a particular instant in time.

Acceleration: Acceleration and deceleration refer to the rate that speed changes.

Velocity: Velocity indicates both speed and direction.

Gravitational acceleration: The earth's gravitational acceleration is approximately 9.8 m/s/s. Slight variations in gravitational acceleration occur relative to location on the earth's surface.

Projectile motion: In many activities, objects or people are projected or propelled into the air. Their trajectories depend on their velocity, height, and angle of release. The forces exerted by gravity and air resistance help determine the resulting flight path.

Projectile motion: With no air resistance, a trajectory angle of 45 degrees produces the greatest distance for objects projected from ground level on a horizontal surface. When the object is projected from above ground level, an angle less than 45 degrees produces the greatest distance.

Forces: Force is a push or pull that changes, or tends to change, the state of motion of an object. Internal forces are muscle contractions. External forces are gravity, air resistance, friction, and reaction forces.

Ground reaction forces (GRF): A person standing on the surface of the earth is pulled by gravity toward the earth's core. The earth reacts against the downward force exerted by the person by pushing upward with an equal and opposing force.

Mass: Mass is synonymous with inertia: the more mass, the more inertia.

Inertia: Inertia is characterized by resistance and persistence. All objects resist movement of their inertia. Once movement is initiated, an object's mass (and inertia) is expressed by a tendency to continue moving at a uniform speed in a straight line unless gravity, air resistance, or friction intervenes.

Newton II: The acceleration of an object or person is inversely proportional to its mass.

Impulse: An object's acceleration is proportional to the force that it applies and the time duration the force acts. Force multiplied by time is called impulse. Force which is applied to a body over a large time frame and to a large area helps to avoid injury when the body comes to a stop or when it stops a moving object.

Momentum: Momentum describes the quantity of motion. An increase in mass or velocity increases momentum.

Newton III: All actions cause reactions. Muscular force applied by an athlete against the earth's surface is an action. The earth's push against a person is the reaction. Action and reaction are colinear forces, both being equal and opposite.

Work: Mechanical work is force multiplied by the distance through which force is applied.

Power: Power is the rate at which work is done.

Energy: There are three types of mechanical energy: kinetic energy, potential energy, and strain energy.

Kinetic energy is the energy that an object possesses by virtue of its motion.

Potential energy (also called gravitational potential energy) is the energy that an object possesses when at a distance above the earth's surface.

Strain energy is the object's capacity to do mechanical work when it recoils after being pulled or pushed out of its normal shape. Strain energy is considered a form of potential energy.

Coefficient of restitution: The rebound of a ball depends on the elastic recoil of both the ball and the object with which it collides. The velocity of the ball, the angle of impact, and factors like temperature and friction affect the manner in which a ball rebounds.

Pressure: Pressure is reduced the larger the area over which a force (load) is spread.

Friction: When two objects slide against each other, static friction resists the initiation of motion and sliding friction resists the sliding motion that occurs. Sliding friction is always less that static friction. Four factors affect static and sliding friction: the forces pressing the contacting surfaces together, the actual contact area between the two surfaces, the nature and type of the materials in contact, and the relative motion between the two surfaces. Rolling friction occurs when a round object rolls against a contacting surface. Rolling friction is significantly less that sliding friction. Rolling friction is influenced by the forces pressing contacting surfaces together, the nature and type of the materials in contact, and the diameter of the rolling object.

Levers: Levers are simple machines that transmit mechanical energy. A lever incorporates a rigid object that rocks or rotates around an axis or fulcrum. Force is applied at one position on the lever, and a resistance applies its own force at another. The two most important functions of a lever system are magnification of force and magnification of speed and distance. There are three classes of levers. First class levers can be made to magnify either force or speed and distance. Second class levers magnify force at the expense of speed and distance. Third class levers magnify speed and distance at the expense of force. Third class levers predominate in the human body. Most muscles in the human body apply great force in order to move
light resistances over large distances at great speed.

Torque: Levers produce a turning effect called torque. Torque is increased by magnifying the applied force and/or the distance from the axis of rotation that force is applied.

Angular velocity: Angular velocity is synonymous with rate of spin. It refers to the angle/degrees/radians/revs completed in a particular time frame in a specific direction.

Centripetal force: All objects that rotate or swing have an inward pulling force, called a centripetal force, that acts toward the axis of rotation. Centripetal force counteracts the inertial desire of objects to travel in a straight line. A centripetal force has an equal and opposite force called a centrifugal force, which acts away from the axis of rotation. Centripetal and centrifugal forces do not exist in the absence of rotation.

Inertia: The inertia of all objects makes them resist rotation. Once forced to rotate, however, an object's inertia is expressed by its wanting to continue rotating.

Rotational inertia: Rotary inertia, also called moment of inertia, varies according to the mass of a spinning object and the way its mass is distributed. The greater the distance that is spread out from its axis of rotation, the greater the rotary inertia. The more compressed that mass is, relative to the axis of rotation, the greater the reduction of rotary inertia.

Angular momentum: Angular momentum is the rotary equivalent of linear momentum. It describes the quantity of rotary momentum. The angular momentum of an object is determined by the product of its mass, angular velocity, and the distribution of its mass.

Conservation of Angular Momentum: In flights of short duration (e.g., diving, long jump, gymnastics), the amount of angular momentum generated by an athlete at takeoff remains the same for the duration of the flight. This indicates that the athlete's angular momentum is conserved. When an athlete's angular momentum is conserved, the rate of spin (angular velocity) increases or decreases in relation to changes in the distribution of the mass.

Body tilt: The body tilt technique of twisting requires athletes to be somersaulting before initiating the twist. This technique uses specific arm actions to tilt the body out of the somersaulting axis. The action transfers angular momentum from the somersault axis to the twist axis. Athletes then twist and somersault simultaneously. When the body tilt is removed, the twist is eliminated and the somersault continues.

Stability: Stability implies resistance against the loss of equilibrium. There are two types of stability: linear and rotary stability. At rest, a person's linear stability is proportional to the mass and the frictional forces occurring between the person' and any supporting surfaces. While moving, a person's linear stability is directly related to momentum. The more massive the athlete and the faster his movements, the greater the person's linear stability. Rotary stability implies resistance against being tipped over and upended. It also indicates resistance of rotatingobject or person against a reduction in rate of spin. A person's resistance against being tipped over or upended increases if (a) the area of the supporting base is enlarged, (b) the person's line of gravity falls with the boundaries of the supporting base, (c)the person lowers the center of
gravity, (d) the person increases the body mass, (e) the person's supporting base extends toward an oncoming force, or (f) the line of gravity shifts toward an oncoming force. Some activities require minimal stability. When people (athletes) need to move quickly in any direction keep supporting bases relatively small and centralize the lines of gravity. In situations where objects rotate, rotary stability is proportional to angular momentum. Rotary stability increases as mass and angular velocity increase, and as mass is extended farther from the axis of rotation.

Fluid forces: person or object moving through a fluid is affected by hydrostatic pressure (exerted by the weight of a fluid), buoyancy (the force opposing gravity that acts on objects partially or totally immersed in a fluid), drag (the force opposing motion through a fluid), and lift (the force acting perpendicularly to motion that deflects an object from its original pathway).

Buoyancy: The buoyant force acting on an athlete is equal to the weight of the fluid that a person's body displaces when immersed in the fluid. The center of buoyancy is the place where the buoyant force concentrates its upward thrust on an object immersed in a fluid. The center of buoyancy is usually positioned higher on a person's body than is the center of gravity.

Laminar flow: Laminar flow, which is smooth and regular, occurs around an object when fluid flow is slow.

Turbulent flow: Turbulent flow, which is disturbed and rough, occurs at high velocities. Turbulent flow generates more drag than laminar flow.

Surface drag: Surface drag is also called skin friction or viscous drag. The amount of surface drag is determined by the relative motion of object and fluid, the area of surface exposed to the flow, the roughness of the object's surface, and the fluid viscosity.

Profile drag: Form drag is also called shape drag or form drag. The amount of profile drag is determined by the relative motion of object and fluid, the pressure differential between the leading and trailing edges of the object, and the amount of surface acting at right angles to the flow.

Drafting: At high velocities turbulent flow produces a low pressure wake acting to the rear of an object. This low pressure area is used in sport for drafting or slipstreaming.

Drag forces: Drag forces are affected by temperature, pressure, fluid density, and humidity.

Lift forces: Athletes and objects are affect by lift forces that depend on the relative motion of the object and the fluid, the angle of the object relative to the flow of the fluid, the size of the surface area angled into the fluid flow, and the nature of the fluid.

Propulsive forces: Swimmers angle their hands and feet to create lift, which can act as a propulsive force. At certain phases in the hand and leg actions of a swimmer, the resultant of lift and drag forces can act as a propulsive force.

Magnus effect: A spinning object (e.g., ball) traveling through the air builds up high pressure on the side spinning into the airflow. Low pressure occurs on the side spinning with the airflow. The ball is deflected from high pressure to low pressure. This phenomenon is called the Magnus effect.