Velocity (metric system) as metres per second (m/s) or as the SI base unit of (m⋅s). For example, "5 metres per second" is a scalar, whereas "5 metres per second east" is a vector. If there is a change in speed, direction or both, then the object has a changing velocity and is said to be undergoing an "acceleration". To have a constant velocity, an object must have a constant speed in a constant direction. Constant direction constrains the object to motion in a straight path thus, a constant velocity means motion in a straight line at a constant speed. For
Escape velocity cases, the spacecraft may be first placed in a parking orbit (e.g. a low Earth orbit at 160–2,000 km) and then accelerated to the escape velocity at that altitude, which will be slightly lower (about 11.0 km/s at a low Earth orbit of 200 km). The required additional change in speed, however, is far less because the spacecraft already has significant orbital velocity (in low Earth orbit speed is approximately 7.8 km/s, or 28,080 km/h). The escape velocity at a given height is formula_15 times the speed in a circular orbit at the same height, (compare this with the velocity