Short answers, pulled from the story.
Velocity is a vector quantity that specifies both the magnitude and direction of motion, while speed is a scalar that specifies magnitude only. For example, "5 metres per second" is a speed, while "5 metres per second east" is a velocity.
Velocity is measured in metres per second (m/s) in the International System of Units (SI). This unit comes from dividing the change in position, measured in metres, by the change in time, measured in seconds.
Instantaneous velocity is the limit of average velocity as the time interval approaches zero, which is mathematically the derivative of position with respect to time. It can be thought of as the velocity an object would continue at if it stopped accelerating at that exact moment.
The escape velocity from Earth's surface is about 11,200 metres per second. It is independent of direction, meaning any object reaching that speed will escape Earth's gravity as long as its path is unobstructed.
Momentum is the product of an object's mass and its velocity vector, making it a vector quantity. Kinetic energy depends on the square of the velocity, which removes directional information, making it a scalar quantity.
Kepler's laws of planetary motion describe the relationships that hold when only radial inverse-square forces, such as gravity, act on an orbiting body. Under those conditions, angular momentum is constant, transverse speed is inversely proportional to distance from the origin, and the rate at which orbital area is swept out remains constant.